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  • 1.
    Agosta, Salvatore J
    et al.
    University of Toronto.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Brooks, Daniel R
    University of Toronto.
    How specialists can be generalists: resolving the “parasite paradox” and implications for emerging infectious disease2010In: Zoologia, ISSN 1984-4670, Vol. 27, no 2, p. 151-162Article in journal (Refereed)
    Abstract [en]

    The parasite paradox arises from the dual observations that parasites (broadly construed, including phy- tophagous insects) are resource specialists with restricted host ranges, and yet shifts onto relatively unrelated hosts are common in the phylogenetic diversification of parasite lineages and directly observable in ecological time. We synthe- size the emerging solution to this paradox: phenotypic flexibility and phylogenetic conservatism in traits related to resource use, grouped under the term ecological fitting, provide substantial opportunities for rapid host switching in changing environments, in the absence of the evolution of novel host-utilization capabilities. We discuss mechanisms behind ecological fitting, its implications for defining specialists and generalists, and briefly review empirical examples of host shifts in the context of ecological fitting. We conclude that host shifts via ecological fitting provide the fuel for the expansion phase of the recently proposed oscillation hypothesis of host range and speciation, and, more generally, the generation of novel combinations of interacting species within the geographic mosaic theory of coevolution. Finally, we conclude that taxon pulses, driven by climate change and large-scale ecological perturbation are drivers of biotic mixing and resultant ecological fitting, which leads to increased rates of rapid host switching, including the agents of Emerging Infectious Disease.

  • 2.
    Audusseau, Helene
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Implications of a temperature increase for host plant range: predictions for a butterfly2013In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 3, no 9, p. 3021-3029Article in journal (Refereed)
    Abstract [en]

    Although changes in phenology and species associations are relatively well-documented responses to global warming, the potential interactions between these phenomena are less well understood. In this study, we investigate the interactions between temperature, phenology (in terms of seasonal timing of larval growth) and host plant use in the polyphagous butterfly Polygonia c-album. We found that the hierarchy of larval performance on three natural host plants was not modified by a temperature increase as such. However, larval performance on each host plant and temperature treatment was affected by rearing season. Even though larvae performed better at the higher temperature regardless of the time of the rearing, relative differences between host plants changed with the season. For larvae reared late in the season, performance was always better on the herbaceous plant than on the woody plants. In this species, it is likely that a prolonged warming will lead to a shift from univoltinism to bivoltinism. The demonstrated interaction between host plant suitability and season means that such a shift is likely to lead to a shift in selective regime, favoring specialization on the herbaceous host. Based on our result, we suggest that host range evolution in response to temperature increase would in this species be highly contingent on whether the population undergoes a predicted shift from one to two generations. We discuss the effect of global warming on species associations and the outcome of asynchrony in rates of phenological change.

  • 3.
    Audusseau, Hélène
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. Paris-Est Créteil University, France.
    Celorio-Mancera, Maria de la Paz
    Stockholm University, Faculty of Science, Department of Zoology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology.
    Why stay in a bad relationship? The effect of local host phenology on a generalist butterfly feeding on a low-ranked host2016In: BMC Evolutionary Biology, ISSN 1471-2148, E-ISSN 1471-2148, Vol. 16, article id 144Article in journal (Refereed)
    Abstract [en]

    Background: In plant-feeding insects, the evolutionary retention of polyphagy remains puzzling. A better understanding of the relationship between these organisms and changes in the metabolome of their host plants is likely to suggest functional links between them, and may provide insights into how polyphagy is maintained. Results: We investigated the phenological change of Cynoglossum officinale, and how a generalist butterfly species, Vanessa cardui, responded to this change. We used untargeted metabolite profiling to map plant seasonal changes in both primary and secondary metabolites. We compared these data to differences in larval performance on vegetative plants early and late in the season. We also performed two oviposition preference experiments to test females' ability to choose between plant developmental stages (vegetative and reproductive) early and late in the season. We found clear seasonal changes in plant primary and secondary metabolites that correlated with larval performance. The seasonal change in plant metabolome reflected changes in both nutrition and toxicity and resulted in zero survival in the late period. However, large differences among families in larval ability to feed on C. officinale suggest that there is genetic variation for performance on this host. Moreover, females accepted all plants for oviposition, and were not able to discriminate between plant developmental stages, in spite of the observed overall differences in metabolite profile potentially associated with differences in suitability as larval food. Conclusions: In V. cardui, migratory behavior, and thus larval feeding times, are not synchronized with plant phenology at the reproductive site. This lack of synchronization, coupled with the observed lack of discriminatory oviposition, obviously has potential fitness costs. However, this opportunistic behavior may as well function as a source of potential host plant evolution, promoting for example the acceptance of new plants.

  • 4.
    Audusseau, Hélène
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Kolb, Gundula
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Plant Fertilization Interacts with Life History: Variation in Stoichiometry and Performance in Nettle-Feeding Butterflies2015In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, no 5, article id e0124616Article in journal (Refereed)
    Abstract [en]

    Variation in food stoichiometry affects individual performance and population dynamics, but it is also likely that species with different life histories should differ in their sensitivity to food stoichiometry. To address this question, we investigated the ability of the three nettle-feeding butterflies (Aglais urticae, Polygonia c-album, and Aglais io) to respond adaptively to induced variation in plant stoichiometry in terms of larval performance. We hypothesized that variation in larval performance between plant fertilization treatments should be functionally linked to species differences in host plant specificity. We found species-specific differences in larval performance between plant fertilization treatments that could not be explained by nutrient limitation. We showed a clear evidence of a positive correlation between food stoichiometry and development time to pupal stage and pupal mass in Aglais urticae. The other two species showed a more complex response. Our results partly supported our prediction that host plant specificity affects larval sensitivity to food stoichiometry. However, we suggest that most of the differences observed may instead be explained by differences in voltinism (number of generations per year). We believe that the potential of some species to respond adaptively to variation in plant nutrient content needs further attention in the face of increased eutrophication due to nutrient leakage from human activities.

  • 5.
    Audusseau, Hélène
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. Paris-Est Créteil University, France.
    Le Vaillant, Maryline
    Stockholm University, Faculty of Science, Department of Zoology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology.
    Karlsson, Bengt
    Stockholm University, Faculty of Science, Department of Zoology.
    Schmucki, Reto
    Species range expansion constrains the ecological niches of resident butterflies2017In: Journal of Biogeography, ISSN 0305-0270, E-ISSN 1365-2699, Vol. 44, no 1, p. 28-38Article in journal (Refereed)
    Abstract [en]

    Aim: Changes in community composition resulting from environmental changes modify biotic interactions and affect the distribution and density of local populations. Such changes are currently occurring in nettle-feeding butterflies in Sweden where Araschnia levana has recently expanded its range northward and is now likely to interact with resident species (Aglais urticae and Aglais io). Butterfly occurrence data collected over years and across regions enabled us to investigate how a recent range expansion of A. levana may have affected the environmental niche of resident species.

    Location: We focused on two regions of Sweden (Skane and Norrstrom) where A. levana has and has not established and two time periods (2001-2006 and 2009-2012) during its establishment in Skane.

    Methods: We performed two distinct analyses in each region using the PCA-env and the framework described in Broennimann etal. (2012). First, we described the main sources of variation in the environment. Second, in each time period and region, we characterized the realized niches of our focal species across topographic and land use gradients. Third, we quantified overlaps and differences in realized niches between and within species over time.

    Results: In Skane, A. levana has stabilized its distribution over time, while the distribution of the native species has shifted. These shifts depicted a consistent pattern of avoiding overlap between the native species and the environmental space occupied by A. levana, and it was stronger for A. urticae than for A. io. In both regions, we also found evidence of niche partitioning between native species.

    Main conclusions: Interspecific interactions are likely to affect local species distributions. It appears that the ongoing establishment of A. levana has modified local biotic interactions and induced shifts in resident species distributions. Among the mechanisms that can explain such patterns of niche partitioning, parasitoid-driven apparent competition may play an important role in this community.

  • 6.
    Bergström, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Janz, Niklas
    Stockholm University, Faculty of Humanities, Centre for the Study of Cultural Evolution. Stockholm University, Faculty of Science, Department of Zoology.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology.
    Putting more eggs in the best basket: clutch size regulation in the comma butterfly2006In: Ecological Entomology, ISSN 0307-6946, E-ISSN 1365-2311, Vol. 31, no 3, p. 255-260Article in journal (Refereed)
    Abstract [en]

    1. Many studies have identified different factors influencing clutchsize regulation, primarily within various groups of insects. One prediction is that ovipositing females should increase clutch size with host quality. However, in many studies it is not clear whether ovipositing females are responding to host quality or quantity.

    2. Females of the polyphagous comma butterfly, allowed to oviposit on two hosts differing greatly in quality: the preferred host, stinging nettle (Polygonia c-album (L.), wereUrtica dioica L.), and the low-ranked host, birch (Betula pubescens  Ehrh). Ovipositing females were observed visually and clutch sizes were recorded. The experiment was repeated in three different years; in total, 938 observations of oviposition events were made.

    3. In all three years, females ovipositing on (median 1.6–1.85) compared with females ovipositing on 1.0–1.3) three years were pooled.

    4. Thus, on better hosts. It is suggested that the proximate mechanism is likely to be a response to the same stimuli used for female ranking of host plants in the preference hierarchy. U. dioica laid larger clutchesB. pubescens (median. The difference was significant in two out of three years and when allP. c-album females exhibit clutch-size regulation, with larger clutches

  • 7.
    Braga, Mariana P.
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Araujo, Sabrina B. L.
    Agosta, Salvatore
    Brooks, Daniel
    Hoberg, Eric
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Boeger, Walter A.
    Host use dynamics in a heterogeneous fitness landscape generates oscillations in host range and diversification2018In: Evolution, ISSN 0014-3820, E-ISSN 1558-5646, Vol. 72, no 9, p. 1773-1783Article in journal (Refereed)
    Abstract [en]

    Colonization of novel hosts is thought to play an important role in parasite diversification, yet little consensus has been achieved about the macroevolutionary consequences of changes in host use. Here, we offer a mechanistic basis for the origins of parasite diversity by simulating lineages evolved in silico. We describe an individual-based model in which (i) parasites undergo sexual reproduction limited by genetic proximity, (ii) hosts are uniformly distributed along a one-dimensional resource gradient, and (iii) host use is determined by the interaction between the phenotype of the parasite and a heterogeneous fitness landscape. We found two main effects of host use on the evolution of a parasite lineage. First, the colonization of a novel host allowed parasites to explore new areas of the resource space, increasing phenotypic and genotypic variation. Second, hosts produced heterogeneity in the parasite fitness landscape, which led to reproductive isolation and therefore, speciation. As a validation of the model, we analyzed empirical data from Nymphalidae butterflies and their host plants. We then assessed the number of hosts used by parasite lineages and the diversity of resources they encompass. In both simulated and empirical systems, host diversity emerged as the main predictor of parasite species richness.

  • 8.
    Braga, Mariana P.
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Guimarães Jr, Paulo R.
    Wheat, Christopher W.
    Stockholm University, Faculty of Science, Department of Zoology.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Unifying host-associated diversification processes using butterfly-plant networks2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 5155Article in journal (Refereed)
    Abstract [en]

    Explaining the exceptional diversity of herbivorous insects is an old problem in evolutionary ecology. Here we focus on the two prominent hypothesised drivers of their diversification, radiations after major host switch or variability in host use due to continuous probing of new hosts. Unfortunately, current methods cannot distinguish between these hypotheses, causing controversy in the literature. Here we present an approach combining network and phylogenetic analyses, which directly quantifies support for these opposing hypotheses. After demonstrating that each hypothesis produces divergent network structures, we then investigate the contribution of each to diversification in two butterfly families: Pieridae and Nymphalidae. Overall, we find that variability in host use is essential for butterfly diversification, while radiations following colonisation of a new host are rare but can produce high diversity. Beyond providing an important reconciliation of alternative hypotheses for butterfly diversification, our approach has potential to test many other hypotheses in evolutionary biology.

  • 9.
    Braga, Mariana P.
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Landis, Michael
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Ronquist, Fredrik
    Bayesian analysis of host repertoire evolutionManuscript (preprint) (Other academic)
  • 10.
    Braga, Mariana P.
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Landis, Michael
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Ronquist, Fredrik
    Evolution of butterfly-plant networks revealed by Bayesian inference of host repertoireManuscript (preprint) (Other academic)
  • 11.
    Carlsson, Mikael A.
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Bisch-Knaden, Sonja
    Schäpers, Alexander
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Mozuraitis, Raimondas
    Hansson, Bill S.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Odour Maps in the Brain of Butterflies with Divergent Host-Plant Preferences2011In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 6, no 8, article id e24025Article in journal (Refereed)
    Abstract [en]

    Butterflies are believed to use mainly visual cues when searching for food and oviposition sites despite that their olfactory system is morphologically similar to their nocturnal relatives, the moths. The olfactory ability in butterflies has, however, not been thoroughly investigated. Therefore, we performed the first study of odour representation in the primary olfactory centre, the antennal lobes, of butterflies. Host plant range is highly variable within the butterfly family Nymphalidae, with extreme specialists and wide generalists found even among closely related species. Here we measured odour evoked Ca2+ activity in the antennal lobes of two nymphalid species with diverging host plant preferences, the specialist Aglais urticae and the generalist Polygonia c-album. The butterflies responded with stimulus-specific combinations of activated glomeruli to single plant-related compounds and to extracts of host and non-host plants. In general, responses were similar between the species. However, the specialist A. urticae responded more specifically to its preferred host plant, stinging nettle, than P. c-album. In addition, we found a species-specific difference both in correlation between responses to two common green leaf volatiles and the sensitivity to these compounds. Our results indicate that these butterflies have the ability to detect and to discriminate between different plant-related odorants.

  • 12.
    Carlsson, Mikael A.
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Schäpers, Alexander
    Stockholm University, Faculty of Science, Department of Zoology.
    Nässel, Dick R.
    Stockholm University, Faculty of Science, Department of Zoology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Organization of the olfactory system of Nymphalidae butterflies2013In: Chemical Senses, ISSN 0379-864X, E-ISSN 1464-3553, Vol. 38, no 4, p. 355-367Article in journal (Refereed)
    Abstract [en]

    Olfaction is in many species the most important sense, essential for food search, mate finding, and predator avoidance. Butterflies have been considered a microsmatic group of insects that mainly rely on vision due to their diurnal lifestyle. However, an emerging number of studies indicate that butterflies indeed use the sense of smell for locating food and oviposition sites. To unravel the neural substrates for olfaction, we performed an anatomical study of 2 related butterfly species that differ in food and host plant preference. We found many of the anatomical structures and pathways, as well as distribution of neuroactive substances, to resemble that of their nocturnal relatives among the Lepidoptera. The 2 species differed in the number of one type of olfactory sensilla, thus indicating a difference in sensitivity to certain compounds. Otherwise no differences could be observed. Our findings suggest that the olfactory system in Lepidoptera is well conserved despite the long evolutionary time since butterflies and moths diverged from a common ancestor.

  • 13.
    Celorio-Mancera, Maria de la Paz
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Sundmalm, Sara M.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Vogel, Heiko
    Rutishauser, Dorothea
    Stockholm University, Science for Life Laboratory (SciLifeLab).
    Ytterberg, A. Jimmy
    Zubarev, Roman A.
    Stockholm University, Science for Life Laboratory (SciLifeLab).
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Chemosensory proteins, major salivary factors in caterpillar mandibular glands2012In: Insect Biochemistry and Molecular Biology, ISSN 0965-1748, E-ISSN 1879-0240, Vol. 42, no 10, p. 796-805Article in journal (Refereed)
    Abstract [en]

    Research in the field of insect-host plant interactions has indicated that constituents of insect saliva play an important role in digestion and affect host chemical defense responses. However, most efforts have focused on studying the composition and function of regurgitant or saliva produced in the labial glands. Acknowledging the need for understanding the role of the mandibular glands in herbivory, we sought to make a qualitative and semi-quantitative comparison of soluble luminal fractions between mandibular and labial glands of Vanessa gonerilla butterfly larvae. Amylase and lysozyme were inspected as possible major enzymatic activities in the mandibular glands aiding in pre-digestion and antimicrobial defense. Although detected, neither of these enzymatic activities was prominent in the luminal protein preparation of a particular type of gland. Proteins isolated from the glands were identified by mass spectrometry and by searching an EST-library database generated for four other nymphalid butterfly species, in addition to the public NCBI database. The identified proteins were also quantified from thedata using “Quanty”, an in-house program. The proteomic analysis detected chemosensory proteins as the most abundant luminal proteins in the mandibular glands. In comparison to these proteins, the relative amounts of amylase and lysozyme were much lower in both gland types. Therefore, we speculate that the primary role of the mandibular glands in Lepidopteran larvae is chemoreception which may include the detection of microorganisms on plant surfaces, host plant recognition and communication with conspecifics.

  • 14.
    Celorio-Mancera, Maria de la Paz
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Wheat, Christopher W.
    Stockholm University, Faculty of Science, Department of Zoology, Population Genetics.
    Vogel, Heiko
    Söderlind, Lina
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Mechanisms of macroevolution: polyphagous plasticity in butterfly larvae revealed by RNA-Seq2013In: Molecular Ecology, ISSN 0962-1083, E-ISSN 1365-294X, Vol. 22, no 19, p. 4884-4895Article in journal (Refereed)
    Abstract [en]

    Transcriptome studies of insect herbivory are still rare, yet studies in model systems have uncovered patterns of transcript regulation that appear to provide insights into how insect herbivores attain polyphagy, such as a general increase in expression breadth and regulation of ribosomal, digestion- and detoxification-related genes. We investigated the potential generality of these emerging patterns, in the Swedish comma, Polygonia c-album, which is a polyphagous, widely-distributed butterfly. Urtica dioica and Ribes uva-crispa are hosts of P. c-album, but Ribes represents a recent evolutionary shift onto a very divergent host. Utilizing the assembled transcriptome for read mapping, we assessed gene expression finding that caterpillar life-history (i.e. 2nd vs. 4th-instar regulation) had a limited influence on gene expression plasticity. In contrast, differential expression in response to host-plant identified genes encoding serine-type endopeptidases, membrane-associated proteins and transporters. Differential regulation of genes involved in nucleic acid binding was also observed suggesting that polyphagy involves large scale transcriptional changes. Additionally, transcripts coding for structural constituents of the cuticle were differentially expressed in caterpillars in response to their diet indicating that the insect cuticle may be a target for plant defence. Our results state that emerging patterns of transcript regulation from model species appear relevant in species when placed in an evolutionary context.

  • 15.
    Celorio-Mancera, Maria de la Paz
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Ytterberg, A. Jimmy
    Rutishauser, Dorothea
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Zubarev, Roman A.
    Effect of host plant and immune challenge on the levels of chemosensory and odorant-binding proteins in caterpillar salivary glands2015In: Insect Biochemistry and Molecular Biology, ISSN 0965-1748, E-ISSN 1879-0240, Vol. 61, p. 34-45Article in journal (Refereed)
    Abstract [en]

    More than half of the proteome from mandibular glands in caterpillars is represented by chemosensory proteins. Based on sequence similarity, these proteins are putative transporters of ligands to gustatory receptors in sensory organs of insects. We sought to determine whether these proteins are inducible by comparing, both qualitatively and quantitatively, the salivary (mandibular and labial) proteomes from caterpillars (Vanessa cardui) reared on different plants and artificial diet containing either bacteria or bacterial cell-walls. We included a treatment where the caterpillars were switched from feeding on artificial diet to plant material at some point in their development. Additionally, we evaluated the degree of overlap between the proteomes in the hemolymph-filled coelom and salivary glands of caterpillars reared on plant material. We found that the quality and quantity of the identified proteins differed clearly between hemolymph-filled coelome, labial and mandibular glands. Our results indicated that even after molting and two-day feeding on a new diet, protein production is affected by the previous food source used by the caterpillar. Candidate proteins involved in chemosensory perception by insects were detected: three chemosensory (CSPs) and two odorant-binding proteins (OBPs). Using the relative amounts of these proteins across tissues and treatments as criteria for their classification, we detected hemolymph- and mandibular gland-specific CSPs and observed that their levels were affected by caterpillar diet. Moreover, we could compare the protein and transcript levels across tissues and treatment for at least one CSP and one OBP. Therefore, we have identified specific isoforms for testing the role of CSPs and OBPs in plant and pathogen recognition. We detected catalase, immune-related protein and serine proteases and their inhibitors in high relative levels in the mandibular glands in comparison to the labial glands. These findings suggest that the mandibular glands of caterpillars may play an important role protecting the caterpillar from oxidative stress, pathogens and aiding in digestion. Contamination with hemolymph proteins during dissection of salivary glands from caterpillars may occur but it is not substantial since the proteomes from hemolymph, mandibular and labial glands were easily discriminated from each other by principal component analysis of proteomic data.

  • 16.
    de la Paz Celorio-Mancera, Maria
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Population Genetics.
    Wheat, Christopher W.
    Stockholm University, Faculty of Science, Department of Zoology, Population Genetics.
    Huss, Mikael
    Vezzi, Francesco
    Neethiraj, Ramprasad
    Stockholm University, Faculty of Science, Department of Zoology, Population Genetics.
    Reimegård, Johan
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Evolutionary history of host use, rather than plant phylogeny, determines gene expression in a generalist butterfly2016In: BMC Evolutionary Biology, ISSN 1471-2148, E-ISSN 1471-2148, Vol. 16, article id 59Article in journal (Refereed)
    Abstract [en]

    Background: Although most insect species are specialized on one or few groups of plants, there are phytophagous insects that seem to use virtually any kind of plant as food. Understanding the nature of this ability to feed on a wide repertoire of plants is crucial for the control of pest species and for the elucidation of the macroevolutionary mechanisms of speciation and diversification of insect herbivores. Here we studied Vanessa cardui, the species with the widest diet breadth among butterflies and a potential insect pest, by comparing tissue-specific transcriptomes from caterpillars that were reared on different host plants. We tested whether the similarities of gene-expression response reflect the evolutionary history of adaptation to these plants in the Vanessa and related genera, against the null hypothesis of transcriptional profiles reflecting plant phylogenetic relatedness. Result: Using both unsupervised and supervised methods of data analysis, we found that the tissue-specific patterns of caterpillar gene expression are better explained by the evolutionary history of adaptation of the insects to the plants than by plant phylogeny. Conclusion: Our findings suggest that V. cardui may use two sets of expressed genes to achieve polyphagy, one associated with the ancestral capability to consume Rosids and Asterids, and another allowing the caterpillar to incorporate a wide range of novel host-plants.

  • 17.
    Gamberale-Stille, Gabriella
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Schäpers, Alexander
    Stockholm University, Faculty of Science, Department of Zoology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology.
    Selective attention by priming in host search behavior of 2 generalist butterflies2019In: Behavioral Ecology, ISSN 1045-2249, E-ISSN 1465-7279, Vol. 30, no 1, p. 142-149Article in journal (Refereed)
    Abstract [en]

    We show that females of 2 generalist butterflies improve their search efficacy after previous encounters of the same host in a way similar to search-image formation, especially if the butterfly-host relationship is historically old. Thus, by targeting a single host at a time, host search efficacy may be improved and constitute a selection pressure for specialization. This result can help explain the evolutionary trend toward host specialization in phytophagous insects that is not well understood. Abstract In phytophagous insects such as butterflies, there is an evolutionary trend toward specialization in host plant use. One contributing mechanism for this pattern may be found in female host search behavior. Since search attention is limited, generalist females searching for hosts for oviposition may potentially increase their search efficacy by aiming their attention on a single host species at a time, a behavior consistent with search image formation. Using laboratory reared and mated females of 2 species of generalist butterflies, the comma, Polygonia c-album, and the painted lady, Vanessa cardui (Lepidoptera: Nymphalidae), we investigated the probability of finding a specific target host (among nonhost distractors) immediately after being primed with an oviposition experience of the same host as compared with different host in indoor cages. We used species-specific host plants that varied with respect to growth form, historical age of the butterfly-host association, and relative preference ranking. We found improved search efficacy after previous encounters of the same host for some but not all host species. Positive priming effects were found only in hosts with which the butterfly has a historically old relationship and these hosts are sometimes also highly preferred. Our findings provides additional support for the importance of behavioral factors in shaping the host range of phytophagous insects, and show that butterflies can attune their search behavior to compensate for negative effects of divided attention between multiple hosts.

  • 18.
    Gamberale-Stille, Gabriella
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Söderlind, Lina
    Stockholm University, Faculty of Science, Department of Zoology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology.
    Host plant choice in the comma butterfly-larval choosiness may ameliorate effects of indiscriminate oviposition2014In: Insect Science, ISSN 1672-9609, E-ISSN 1744-7917, Vol. 21, no 4, p. 499-506Article in journal (Refereed)
    Abstract [en]

    In most phytophagous insects, the larval diet strongly affects future fitness and in species that do not feed on plant parts as adults, larval diet is the main source of nitrogen. In many of these insect host plant systems, the immature larvae are considered to be fully dependent on the choice of the mothers, who, in turn, possess a highly developed host recognition system. This circumstance allows for a potential mother-offspring conflict, resulting in the female maximizing her fecundity at the expense of larval performance on suboptimal hosts. In two experiments, we aimed to investigate this relationship in the polyphagous comma butterfly, Polygonia c-album, by comparing the relative acceptance of low- and medium-ranked hosts between females and neonate larvae both within individuals between life stages, and between mothers and their offspring. The study shows a variation between females in oviposition acceptance of low-ranked hosts, and that the degree of acceptance in the mothers correlates with the probability of acceptance of the same host in the larvae. We also found a negative relationship between stages within individuals as there was a higher acceptance of lower ranked hosts in females who had abandoned said host as a larva. Notably, however, neonate larvae of the comma butterfly did not unconditionally accept to feed from the least favorable host species even when it was the only food source. Our results suggest the possibility that the disadvantages associated with a generalist oviposition strategy can be decreased by larval participation in host plant choice.

  • 19.
    Heidel-Fischer, Hanna
    et al.
    Department of Entomology, Max Planck Institute for Chemical Ecology.
    Freitak, Dalial
    Department of Entomology, Max Planck Institute for Chemical Ecology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Soderlind, Lina
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Vogel, Heiko
    Department of Entomology, Max Planck Institute for Chemical Ecology.
    Nylin, Soren
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Phylogenetic relatedness and host plant growth form influence gene expression of the polyphagous comma butterfly (Polygonia c-album).2009In: BMC Genomics, ISSN 1471-2164, E-ISSN 1471-2164, Vol. 10, no 1, p. 506-Article in journal (Refereed)
    Abstract [en]

    ABSTRACT: BACKGROUND: The mechanisms that shape the host plant range of herbivorous insect are to date not well understood but knowledge of these mechanisms and the selective forces that influence them can expand our understanding of the larger ecological interaction. Nevertheless, it is well established that chemical defenses of plants influence the host range of herbivorous insects. While host plant chemistry is influenced by phylogeny, also the growth forms of plants appear to influence the plant defense strategies as first postulated by Feeny (the "plant apparency" hypothesis). In the present study we aim to investigate the molecular basis of the diverse host plant range of the comma butterfly (Polygonia c-album) by testing differential gene expression in the caterpillars on three host plants that are either closely related or share the same growth form. RESULTS: In total 120 differentially expressed genes were identified in P. c-album after feeding on different host plants, 55 of them in the midgut and 65 in the restbody of the caterpillars. Expression patterns could be confirmed with an independent method for 14 of 27 tested genes. Pairwise similarities in upregulation in the midgut of the caterpillars were higher between plants that shared either growth form or were phylogenetically related. No known detoxifying enzymes were found to be differently regulated in the midgut after feeding on different host plants. CONCLUSIONS: Our data suggest a complex picture of gene expression in response to host plant feeding. While each plant requires a unique gene regulation in the caterpillar, both phylogenetic relatedness and host plant growth form appear to influence the expression profile of the polyphagous comma butterfly, in agreement with phylogenetic studies of host plant utilization in butterflies.

  • 20.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Ehrlich and Raven Revisited: Mechanisms Underlying Codiversification of Plants and Enemies2011In: Annual Review of Ecology, Evolution and Systematics, ISSN 1543-592X, E-ISSN 1545-2069, Vol. 42, p. 71-89Article, review/survey (Refereed)
    Abstract [en]

    After almost 50 years of scrutiny, the ideas that Ehrlich and Raven presented in their classical paper on the coevolution between butterflies and plants are still very much alive. Much of this interest has involved the potential for codiversification, both in how the interaction itself diversifies and how the interaction affects modes and rates of speciation. Despite high levels of conservatism and specialization, diversification of the interaction appears to be mainly a consequence of host shifts, but this somewhat paradoxical conclusion can be understood by an appreciation of the ecological as well as genetic mechanisms behind host shifts. There are several ways that the interaction can influence speciation, with or without host-plant-based di-vergent selection on reproductive barriers. One current debate is over the relative importance of radiations following shifts to new adaptive zones and elevated rates of speciation in groups with plastic and diverse host use.

  • 21.
    Janz, Niklas
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Bergström, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Johansson, Josefin
    Frequency dependence of host plant choice within and between patches: a large cage experiment2005In: Evolutionary Ecology, ISSN 0269-7653, E-ISSN 1573-8477, Vol. 19, no 3, p. 289-302Article in journal (Refereed)
    Abstract [en]

    Oviposition preference is considered to be one of the most important factors behind patterns of host use among herbivorous insects. However, preference is defined as host plant choice under equal host abundance and availability, and it is likely that frequency-dependent effects will alter the actual pattern of host use beyond what preference trials reveals. The effects of such alterations are poorly known but could be important for the understanding of specialization and host shifts. We investigated how changes in frequency of a preferred and a less preferred host affected movement patterns and egg deposition within and among patches in a polyphagous butterfly, Polygonia c-album. Two experiments were carried out in large (8 × 30 m) outdoor cages, artificially divided into distinct patches with different frequencies of the two hosts: one that allowed for limited movement between patches and one that did not. There was a clear effect of frequency on patch selection; females spent more time in and laid more eggs in patches with a high frequency of the preferred host, which will potentially have a large effect on host use by modifying encounter rates in favor of the preferred host. However, there was no significant frequency-dependent plant choice within patches in any experiment. Instead, results indicate that females are distributing their eggs among plants species according to specific likelihoods of oviposition, independent of encounter rates, which is compatible with a strategy of risk-spreading.

  • 22.
    Janz, Niklas
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Bergström, Anders
    Stockholm University, Faculty of Science, Department of Zoology.
    Sjögren, Anna
    The role of nectar sources for oviposition decisions of the common blue butterfly (Polyommatus icarus)2005In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 109, p. 535-538Article in journal (Refereed)
    Abstract [en]

    Neural limitations on information processing have been shown to play an important role for host plant specialization in herbivorous insects. The necessity of fast and accurate decisions favors the adoption of a few high-contrast signals, which selects against the use of multiple resources. Many species face a similar problem when searching for adult food sources and the simultaneous need to fulfill both search tasks can lead to a potential conflict. Some insects use the same host plant species for both adult and larval nutrition, which makes it possible to decrease the number of search images and thus potentially increase efficiency of the choices. The aim of this study was to investigate if there is a connection between choice of nectar sources and choice of oviposition host plant. In a laboratory experiment, females of Polyommatus icarus preferred to oviposit on Lotus corniculatus plants with flowers over those without flowers. Observations of behavioral sequences also revealed that oviposition often followed immediately after nectaring. The results suggest that nectar availability could play an important role in oviposition decisions of P. icarus and can provide one explanation to why some phytophagous insects not always choose the host plant that gives the best offspring performance.

  • 23.
    Janz, Niklas
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Braga, Mariana P
    Stockholm University, Faculty of Science, Department of Zoology.
    Wahlberg, Niklas
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology.
    On oscillations and flutterings - A reply to Hamm and Fordyce2016In: Evolution, ISSN 0014-3820, E-ISSN 1558-5646, Vol. 70, no 5, p. 1150-1155Article in journal (Refereed)
    Abstract [en]

    The diversification of plant-feeding insects is seen as a spectacular example of evolutionary radiation. Hence, developing hypotheses to explain this diversification, and methods to test them, is an important undertaking. Some years ago, we presented the oscillation hypothesis as a general process that could drive diversification of this and similar interactions, through repeated expansions and contractions of host ranges. Hamm and Fordyce recently presented a study with the outspoken intention of testing this hypothesis where they concluded that the oscillation hypothesis was not supported. We point out several problems with their study, owing both to a misrepresentation of our hypothesis and to the methods. We provide a clarifying description of the oscillation hypothesis, and detail some predictions that follow from it. A reanalysis of the data demonstrated a troubling sensitivity of the "SSE" class of models to small changes in model specification, and we caution against using them for tests of trait-based diversification. Future tests of the hypothesis also need to better acknowledge the processes behind the host range oscillations. We suspect that doing so will resolve some of the apparent conflicts between our hypothesis and the view presented by Hamm and Fordyce.

  • 24.
    Janz, Niklas
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. Stockholm University, Faculty of Humanities, Centre for the Study of Cultural Evolution. Ekologi.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology. Ekologi.
    The oscillation hypothesis of host-plant range and speciation2008In: Specialization, speciation and radiation: the evolutionary biology of herbivorous insects, Berkeley: University of California Press, 2008, p. 203-215Chapter in book (Refereed)
  • 25.
    Janz, Niklas
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. Stockholm University, Faculty of Humanities, Centre for the Study of Cultural Evolution.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology. Zoologisk ekologi.
    Wahlberg, Niklas
    Stockholm University, Faculty of Science, Department of Zoology. Zoologisk ekologi.
    Diversity begets diversity: host expansions and the diversification of plant-feeding insects.2006In: BMC Evol Biol, ISSN 1471-2148, Vol. 6, no 1, p. 4-Article in journal (Refereed)
    Abstract [en]

    Background: Plant-feeding insects make up a large part of earth's total biodiversity. While it has been shown that herbivory has repeatedly led to increased diversification rates in insects, there has been no compelling explanation for how plant-feeding has promoted speciation rates. There is a growing awareness that ecological factors can lead to rapid diversification and, as one of the most prominent features of most insect-plant interactions, specialization onto a diverse resource has often been assumed to be the main process behind this diversification. However, specialization is mainly a pruning process, and is not able to actually generate diversity by itself. Here we investigate the role of host colonizations in generating insect diversity, by testing if insect speciation rate is correlated with resource diversity.

    Results: By applying a variant of independent contrast analysis, specially tailored for use on questions of species richness (MacroCAIC), we show that species richness is strongly correlated with diversity of host use in the butterfly family Nymphalidae. Furthermore, by comparing the results from reciprocal sister group selection, where sister groups were selected either on the basis of diversity of host use or species richness, we find that it is likely that diversity of host use is driving species richness, rather than vice versa.

    Conclusion: We conclude that resource diversity is correlated with species richness in the Nymphalidae and suggest a scenario based on recurring oscillations between host expansions – the incorporation of new plants into the repertoire – and specialization, as an important driving force behind the diversification of plant-feeding insects.

  • 26.
    Janz, Niklas
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. Stockholm University, Faculty of Science, Department of Zoology, Department of Animal Ecology. Stockholm University, Faculty of Humanities, Centre for the Study of Cultural Evolution.
    Söderlind, Lina
    Stockholm University, Faculty of Science, Department of Zoology. Stockholm University, Faculty of Science, Department of Zoology, Department of Animal Ecology.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology. Stockholm University, Faculty of Science, Department of Zoology, Department of Animal Ecology.
    No effect of larval experience on adult host preferences in Polygonia c-album (Lepidoptera: Nymphalidae): on the persistence of Hopkins' host selection principle2009In: Ecological Entomology, ISSN 0307-6946, E-ISSN 1365-2311, Vol. 34, no 1, p. 50-57Article in journal (Refereed)
    Abstract [en]

    1. The possible effect of juvenile imprinting or 'chemical legacy' on the subsequent oviposition - often called the 'Hopkins' host selection principle' - has been a controversial but recurrent theme in the literature on host-plant preference. While it appears possible in principle, experimental support for the hypothesis is equivocal. The present study points out that it is also important to consider its theoretical implications, and asks under what circumstances, if any, it should be favoured by natural selection.

    2. Following this reasoning, it is predicted that host preference in the polyphagous butterfly Polygonia c-album L. (Lepidoptera, Nymphalidae) should not be influenced by larval environment. This was tested by rearing larvae on three natural host plants: the high-ranked Urtica dioica and the medium-ranked Salix cinerea and Ribes uva-crispa, and exposing the naive females to oviposition choices involving the same set of plants.

    3. It was found that larval host plant had no effect on oviposition decisions of the adult female. Hence, the Hopkins' host selection principle does not seem to be applicable in this species.

    4. Based on recent insights on how accuracy of environmental versus genetic information should affect the control of developmental switches, the conditions that could favour the use of juvenile cues in oviposition decisions are discussed. Although the Hopkins' host selection hypothesis cannot be completely ruled out, we argue that the circumstances required for it to be adaptive are so specific that it should not be invoked as a general hypothesis for host selection in plant-feeding insects.

     

  • 27.
    Johansson, Josefin
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. Zoologisk ekologi.
    Bergström, Anders
    Stockholm University, Faculty of Science, Department of Zoology. Zoologisk ekologi.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology. Zoologisk ekologi. Stockholm University, Faculty of Humanities, Centre for the Study of Cultural Evolution.
    The benefit of additional oviposition targets for a polyphagous butterfly2007In: Journal of Insect Science, ISSN 1536-2442, Vol. 7, no 3Article in journal (Refereed)
    Abstract [en]

    While the reasons for the prevalence of specialists over generalists among herbivorous insects have been at the focus of much interest, less effort has been put into understanding the polyphagous exceptions. Recent studies have suggested that these exceptions may be important for insect diversification, which calls for a better understanding of the potential factors that can lead to an increased host plant repertoire. Females of the Nymphalid butterfly, Polygonia c-album, were used to test if egg output and/or likelihood of finding a host increased with the addition of a secondary host. There was no effect of prior eggs on the host for willingness to oviposit on a plant. The main experiments were conducted both in small laboratory cages and in large outdoor experimental arenas. No positive effect was found when another oviposition target was added in small cages in the laboratory. On the other hand, in the outdoor arenas the females more often found a host to oviposit on and had a higher egg output when they had access to an additional host, even though the second host was lower in their preference hierarchy. The difference between these experiments was attributed to searching for acceptable host plants within a patch, a factor that was included in the large cages but not in the small. When host availability is limited, adding oviposition targets can potentially act to counterbalance specialization and thus favor the evolution of generalization.

  • 28.
    Kodandaramaiah, Ullasa
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Weingartner, Elisabet
    Stockholm University, Faculty of Science, Department of Zoology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Dalén, L.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology.
    Population structure in relation to host-plant ecology and Wolbachia infestation in the comma butterfly2011In: Journal of Evolutionary Biology, ISSN 1010-061X, E-ISSN 1420-9101, Vol. 24, no 10, p. 2173-2185Article in journal (Refereed)
    Abstract [en]

    Experimental work on Polygonia c-album, a temperate polyphagous butterfly species, has shown that Swedish, Belgian, Norwegian and Estonian females are generalists with respect to host-plant preference, whereas females from UK and Spain are specialized on Urticaceae. Female preference is known to have a strong genetic component. We test whether the specialist and generalist populations form respective genetic clusters using data from mitochondrial sequences and 10 microsatellite loci. Results do not support this hypothesis, suggesting that the specialist and generalist traits have evolved more than once independently. Mitochondrial DNA variation suggests a rapid expansion scenario, with a single widespread haplotype occurring in high frequency, whereas microsatellite data indicate strong differentiation of the Moroccan population. Based on a comparison of polymorphism in the mitochondrial data and sequences from a nuclear gene, we show that the diversity in the former is significantly less than that expected under neutral evolution. Furthermore, we found that almost all butterfly samples were infected with a single strain of Wolbachia, a maternally inherited bacterium. We reason that indirect selection on the mitochondrial genome mediated by a recent sweep of Wolbachia infection has depleted variability in the mitochondrial sequences. We also surmise that P. c-album could have expanded out of a single glacial refugium and colonized Morocco recently.

  • 29.
    Kodandaramaiah, Ullasa
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Weingartner, Elisabet
    Stockholm University, Faculty of Science, Department of Zoology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Leski, Michael
    Slove, Jessica
    Stockholm University, Faculty of Science, Department of Zoology.
    Warren, Andrew
    McGuire Center for Lepidoptera and Biodiversity, Florida Museum of Natural History, University of Florida.
    Validity of the subspecies paradigm - a case study of the nymphalid butterfly Polygonia faunusIn: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203Article in journal (Refereed)
    Abstract [en]

    Subspecies are commonly used taxonomic units to formally describe intraspecific geographic variation in morphological traits. However, the concept of subspecies is not clearly defined, and there is little agreement about what they represent in terms of evolutionary units, and whether they can be used as reliably useful units in conservation, evolutionary theory and taxonomy. Although the validity of subspecies has been tested using a multi-marker genetic approach in vertebrates, such studies have been rare in invertebrates. We here test the validity of well-characterized subspecies in the butterfly Polygonia faunus using a combination of mitochondrial sequences and eight microsatellites. We have also investigated the phylogeographic Structure of P. faunus and test whether similarities in host-plant use among populations is related to genetic similarity. Neither the nuclear nor the mitochondrial dataset corroborated subspecies groupings. We found three welldefined genetic clusters corresponding to California, Arizona and (New Mexico + Colorado). There was little structuring among the remaining populations, probably due to gene flow across populations. We found no support for the hypothesis that similarities in host use are related to genetic proximity. The results indicate that the species underwent a recent rapid expansion, probably from two glacial refugia in western North America. The mitochondrial haplotype network indicates at least two independent expansion phases into eastern North America. Ourresults clearly demonstrate that subspecies in P. faunus do not conform to the structuring of genetic variation. More studies on insects and other invertebrates are needed to understand how widespread this phenomenon is. Results in this study will be crucial in designing further experiments to understand the evolution of host plant utilization in this species.

  • 30.
    Kodandaramaiah, Ullasa
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Weingartner, Elisabet
    Stockholm University, Faculty of Science, Department of Botany.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Leski, Michael
    Slove, Jessica
    Stockholm University, Faculty of Science, Department of Zoology.
    Warren, Andrew
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology.
    Investigating concordance among genetic data, subspecies circumscriptions and hostplant use in the nymphalid butterfly polygonia faunus2012In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 7, no 7, p. e41058-Article in journal (Refereed)
    Abstract [en]

    Subspecies are commonly used taxonomic units to formally describe intraspecific geographic variation in morphological traits. However, the concept of subspecies is not clearly defined, and there is little agreement about what they represent in terms of evolutionary units, and whether they can be used as reliably useful units in conservation, evolutionary theory and taxonomy. We here investigate whether the morphologically well-characterized subspecies in the North American butterfly Polygonia faunus are supported by genetic data from mitochondrial sequences and eight microsatellite loci. We also investigate the phylogeographic structure of P. faunus and test whether similarities in host-plant use among populations are related to genetic similarity. Neither the nuclear nor the mitochondrial data corroborated subspecies groupings. We found three well defined genetic clusters corresponding to California, Arizona and (New Mexico+Colorado). There was little structuring among the remaining populations, probably due to gene flow across populations. We found no support for the hypothesis that similarities in host use are related to genetic proximity. The results indicate that the species underwent a recent rapid expansion, probably from two glacial refugia in western North America. The mitochondrial haplotype network indicates at least two independent expansion phases into eastern North America. Our results clearly demonstrate that subspecies in P. faunus do not conform to the structuring of genetic variation. More studies on insects and other invertebrates are needed to better understand the scope of this phenomenon. The results of this study will be crucial in designing further experiments to understand the evolution of hostplant utilization in this species.

  • 31.
    Larsdotter-Mellström, Helena
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. University of Western Australia, Australia.
    Eriksson, Kerstin
    Stockholm University, Faculty of Science, Department of Zoology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology.
    Carlsson, Mikael A.
    Stockholm University, Faculty of Science, Department of Zoology.
    Male butterflies use an anti-aphrodisiac pheromone to tailor ejaculates2016In: Functional Ecology, ISSN 0269-8463, E-ISSN 1365-2435, Vol. 30, no 2, p. 255-261Article in journal (Refereed)
    Abstract [en]

    When females mate with multiple partners, the risk of sperm competition depends on female mating history. To maximize fitness, males should adjust their mating investment according to this risk. In polyandrous butterflies, males transfer a large, nutritious ejaculate at mating. Larger ejaculates delay female remating and confer an advantage in sperm competition. We test whether male ejaculate size in the butterfly Pieris napi (Lepidoptera) varies with female mating history and thus sperm competition, and whether males assess sperm competition using the male-transferred anti-aphrodisiac methyl salicylate (MeS) as a cue. Both sexes responded physiologically to MeS in a dose-dependent manner. Males, however, were more sensitive to MeS than females. Ejaculates transferred by males mating with previously mated females were on average 26% larger than ejaculates transferred by males mating with virgin females, which conforms to sperm competition theory and indicates that males tailored their reproductive investment in response to sperm competition. Furthermore, ejaculates transferred by males mating with virgin females with artificially added MeS were also 26% larger than ejaculates transferred to control virgin females. Male-transferred anti-aphrodisiac pheromone not only functions as a male deterrent, but also carries information on female mating history and thus allows males to assess sperm competition.

  • 32.
    Larsdotter-Mellström, Helena
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. The University of Western Australia, Australia.
    Eriksson, Kerstin
    Liblikas, Ilme
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Borg-Karlsson, Anna K.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Carlsson, Mikael A.
    Stockholm University, Faculty of Science, Department of Zoology.
    It's All in the Mix: Blend-Specific Behavioral Response to a Sexual Pheromone in a Butterfly2016In: Frontiers in Physiology, ISSN 1664-042X, E-ISSN 1664-042X, Vol. 7, article id 68Article in journal (Refereed)
    Abstract [en]

    Among insects, sexual pheromones are typically mixtures of two to several components, all of which are generally required to elicit a behavioural response. Here we show for the first time that a complete blend of sexual pheromone components is needed to elicit a response also in a butterfly. Males of the Green-veined White, Pieris napi, emit an aphrodisiac pheromone, citral, from wing glands. This pheromone is requisite for females to accept mating with a courting male. Citral is a mixture of the two geometric isomers geranial (E-isomer) and neral (Z-isomer) in an approximate 1:1 ratio. We found that both these compounds are required to elicit acceptance behaviour, which indicates synergistic interaction between processing of the isomers. Using functional Ca2+ imaging we found that geranial and neral evoke significantly different but overlapping glomerular activity patterns in the antennal lobe, which suggests receptors with different affinity for the two isomers. However, these glomeruli were intermingled with glomeruli responding to ,for example, plant-related compounds, i.e. no distinct subpopulation of pheromone-responding glomeruli as in moths and other insects. In addition, these glomeruli showed lower specificity than pheromone-activated glomeruli in moths. We could, however, not detect any mixture interactions among four identified glomeruli, indicating that the synergistic effect may be generated at a higher processing level. Furthermore, correlations between glomerular activity patterns evoked by the single isomers and the blend did not change over time.

  • 33.
    Nylin, Sören
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Agosta, Salvatore
    Bensch, Staffan
    Boeger, Walter A.
    P. Braga, Mariana
    Stockholm University, Faculty of Science, Department of Zoology.
    Brooks, Daniel R.
    Forister, Matthew L.
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hoberg, Eric P.
    Nyman, Tommi
    Schäpers, Alexander
    Stockholm University, Faculty of Science, Department of Zoology.
    Stigall, Alycia L.
    Wheat, Christopher W.
    Stockholm University, Faculty of Science, Department of Zoology.
    Österling, Martin
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Embracing Colonizations: A New Paradigm for Species Association Dynamics2018In: Trends in Ecology & Evolution, ISSN 0169-5347, E-ISSN 1872-8383, Vol. 33, no 1, p. 4-14Article, review/survey (Refereed)
    Abstract [en]

    Parasitehost and insectplant research have divergent traditions despite the fact that most phytophagous insects live parasitically on their host plants. In parasitology it is a traditional assumption that parasites are typically highly specialized; cospeciation between parasites and hosts is a frequently expressed default expectation. Insectplant theory has been more concerned with host shifts than with cospeciation, and more with hierarchies among hosts than with extreme specialization. We suggest that the divergent assumptions in the respective fields have hidden a fundamental similarity with an important role for potential as well as actual hosts, and hence for host colonizations via ecological fitting. A common research program is proposed which better prepares us for the challenges from introduced species and global change.

  • 34.
    Nylin, Sören
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology. Stockholm University, Faculty of Humanities, Centre for the Study of Cultural Evolution.
    Butterfly host plant range: an example of plasticity as a promoter of speciation?2009In: Evolutionary Ecology, ISSN 0269-7653, E-ISSN 1573-8477, Vol. 23, no 1, p. 137-146Article in journal (Refereed)
    Abstract [en]

    Mary Jane West-Eberhard has suggested that plasticity may be of primary importance in promoting evolutionary innovation and diversification. Here, we explore the possibility that the diversification of phytophagous insects may have occurred through such a process, using examples from nymphalid butterflies. We discuss the ways in which host plant range is connected to plasticity and present our interpretation of how West-Eberhard's scenario may result in speciation driven by plasticity in host utilization. We then review some of the evidence that diversity of plant utilization has driven the diversification of phytophagous insects and finally discuss whether this suggests a role for plasticity-driven speciation. We find a close conceptual connection between our theory that the diversification of phytophagous insects has been driven by oscillations in host range, and our personal interpretation of the most efficient way in which West-Eberhard's theory could account for plasticity-driven speciation. A major unresolved issue is the extent to which a wide host plant range is due to adaptive plasticity with dedicated modules of genetic machinery for utilizing different plants.

  • 35.
    Nylin, Sören
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Slove, Jessica
    Stockholm University, Faculty of Science, Department of Zoology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    HOST PLANT UTILIZATION, HOST RANGE OSCILLATIONS AND DIVERSIFICATION IN NYMPHALID BUTTERFLIES: A PHYLOGENETIC INVESTIGATION2014In: Evolution, ISSN 0014-3820, E-ISSN 1558-5646, Vol. 68, no 1, p. 105-124Article in journal (Refereed)
    Abstract [en]

    It has been suggested that phenotypic plasticity is a major factor in the diversification of life, and that variation in host range in phytophagous insects is a good model for investigating this claim. We explore the use of angiosperm plants as hosts for nymphalid butterflies, and in particular the evidence for past oscillations in host range and how they are linked to host shifts and to diversification. At the level of orders of plants, a relatively simple pattern of host use and host shifts emerges, despite the 100 million years of history of the family Nymphalidae. We review the evidence that these host shifts and the accompanying diversifications were associated with transient polyphagous stages, as suggested by the oscillation hypothesis. In addition, we investigate all currently polyphagous nymphalid species and demonstrate that the state of polyphagy is rare, has a weak phylogenetic signal, and a very apical distribution in the phylogeny; we argue that these are signs of its transient nature. We contrast our results with data from the bark beetles Dendroctonus, in which a more specialized host use is instead the apical state. We conclude that plasticity in host use is likely to have contributed to diversification in nymphalid butterflies.

  • 36.
    Nylin, Sören
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Söderlind, Lina
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Gamberale-Stille, Gabriella
    Stockholm University, Faculty of Science, Department of Zoology, Ethology.
    Audusseau, Hélène
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Celorio-Mancera, Maria de la Paz
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Sperling, Felix A. H.
    Vestiges of an ancestral host plant: preference and performance in the butterfly Polygonia faunus and its sister species P. c-album2015In: Ecological Entomology, ISSN 0307-6946, E-ISSN 1365-2311, Vol. 40, no 3, p. 307-315Article in journal (Refereed)
    Abstract [en]

    1. In the study of the evolution of insect-host plant interactions, important information is provided by host ranking correspondences among female preference, offspring preference, and offspring performance. Here, we contrast such patterns in two polyphagous sister species in the butterfly family Nymphalidae, the Nearctic Polygonia faunus, and the Palearctic P. c-album. 2. These two species have similar host ranges, but according to the literature P. faunus does not use the ancestral host plant clade-the urticalean rosids'. Comparisons of the species can thus test the effects of a change in insect-plant associations over a long time scale. Cage experiments confirmed that P. faunus females avoid laying eggs on Urtica dioica (the preferred host of P. c-album), instead preferring Salix, Betula, and Ribes.3. However, newly hatched larvae of both species readily accept and grow well on U. dioica, supporting the general theory that evolutionary changes in host range are initiated through shifts in female host preferences, whereas larvae are more conservative and also can retain the capacity to perform well on ancestral hosts over long time spans.4. Similar rankings of host plants among female preference, offspring preference, and offspring performance were observed in P. c-album but not in P. faunus. This is probably a result of vestiges of larval adaptations to the lost ancestral host taxon in the latter species. 5. Female and larval preferences seem to be largely free to evolve independently, and consequently larval preferences warrant more attention.

  • 37.
    Schäpers, Alexander
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Carlsson, Mikael A.
    Stockholm University, Faculty of Science, Department of Zoology, Functional Morphology.
    Gamberale Stille, Gabriella
    Stockholm University, Faculty of Science, Department of Zoology, Ethology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    The Role of Olfactory Cues for the Search Behavior of a Specialist and Generalist Butterfly2015In: Journal of insect behavior, ISSN 0892-7553, E-ISSN 1572-8889, Vol. 28, no 1, p. 77-87Article in journal (Refereed)
    Abstract [en]

    Searching for resources is often a challenging task, especially for small organisms such as insects. Complex stimuli have to be extracted from the environment and translated into a relevant behavioral output. A first step in this process is to investigate the relative roles of the different senses during search for various resources. While the role of olfaction is well documented in nocturnal moths, the olfactory abilities of the closely related diurnal butterflies are poorly explored. Here we investigated how olfactory information is used in the search for host plants and asked if these abilities varied with levels of stimulus complexity. Thus, we tested two nymphalid butterfly species with divergent host plant range in a two-choice olfactometer testing different combinations of host and non-host plants. The experiments show both the monophagous Aglais urticae and the polyphagous Polygonia c-album could navigate towards an odor source, but this ability varied with context. While mated females exhibited a preference for their host plant, unmated females of both species did not show a preference for host plant cues. Furthermore, both species showed inabilities to make fine-tuned decisions between hosts. We conclude that olfactory cues are important for butterflies to navigate towards targets. We argue that there are limitations on how much information can be extracted from host volatiles. These results are discussed in the light of neural processing limitations and degree of host plant specialization, suggesting the necessity of other sensory modalities to sharpen the decision process and facilitate the final oviposition event.

  • 38.
    Schäpers, Alexander
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Carlsson, Mikael A.
    Stockholm University, Faculty of Science, Department of Zoology, Functional Morphology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Specialist and generalist oviposition strategies in butterflies: maternal care or precocious young?2016In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 180, no 2, p. 335-343Article in journal (Refereed)
    Abstract [en]

    Herbivorous insects specialized on a narrow set of plants are believed to be better adapted to their specific hosts. This hypothesis is supported by observations of herbivorous insect species with a broader diet breadth which seemingly pay a cost through decreased oviposition accuracy. Despite many studies investigating female oviposition behavior, there is a lack of knowledge on how larvae cope behaviorally with their mothers' egg-laying strategies. We have examined a unique system of five nymphalid butterfly species with different host plant ranges that all feed on the same host plant. The study of this system allowed us to compare at the species level how oviposition preference is related to neonate larval responses in several disadvantageous situations. We found a general co-adaptation between female and larval abilities, where species with more discriminating females had larvae that were less able to deal with a suboptimal initial feeding site. Conversely, relatively indiscriminate females had more precocious larvae with better abilities to cope with suboptimal sites. Despite similarities between the tested species with similar host ranges, there were also striking differences. Generalist and specialist species can be found side by side in many clades, with each clade having a specific evolutionary history. Such clade-specific, phylogenetically determined preconditions apparently have affected how precisely a broad or narrow diet breadth can be realized.

  • 39.
    Schäpers, Alexander
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Gonzalez-Voyer, Alejandro
    Stockholm University, Faculty of Science, Department of Zoology, Ethology.
    Wang, Houshuai
    Wahlberg, Niklas
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Clutch size and host use in butterflies - and how to measure diet breadthManuscript (preprint) (Other academic)
    Abstract [en]

    The utilization of host plants is a central aspect of herbivorous insect life-history and known to promote processes of diversification in this group. In species that aggregate their eggs, female selection of a suitable egg-laying site is especially important, since a large proportion of the realized fitness will depend on few oviposition events. A cluster of larvae also requires a large resource to complete development and thus resource size may further limit the range of suitable hosts. We investigated whether there is a relationship between clutch size and diet breadth for 206 nymphalid butterfly species, using phylogenetic comparative methods. Results were consistent across several taxonomic and phylogenetic diet breadth measures, suggesting that some taxonomic measures may be as good approximations as the more cumbersome estimates based on phylogenetic distance. Treating diet breadth and clutch size as continuous data indicated no relationship between the traits, while categorizing them into binary form showed that they evolve in a correlated fashion. The discordance between analyses indicated that clutch size may be constrained among extreme generalists, as polyphagous clutch layers were rare. We found clutch-laying to be a relatively conserved trait in the phylogeny and less flexible than variation in degree of host plant specialization. Host plant growth form did not influence the clutch size diet breath relationship, but was weakly correlated with both factors. We discuss the general role of conservative life-history traits, such as clutch size, for the evolutionary dynamics of more labile traits such as diet breadth among phytophagous insects.

  • 40.
    Slove, Jessica
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Phylogenetic analysis of the latitude-niche breadth hypothesis in the butterfly subfamily Nymphalinae2010In: Ecological Entomology, ISSN 0307-6946, E-ISSN 1365-2311, Vol. 35, no 6, p. 768-774Article in journal (Refereed)
    Abstract [en]

    One possible explanation for the latitudinal gradient in species richness often demonstrated is a related gradient in niche breadth, which may allow for denser species packing in the more stable environments at low latitudes.

    The evidence for such a gradient is, however, ambiguous, and the results have varied as much as the methods. Several studies have considered the non-independence of species, but few have performed explicit phylogenetic analyses.

    In the present study, we tested for a correlation between diet breadth and latitude of distribution in Nymphalinae butterflies using generalised estimating equations (GEE) and accounting for phylogenetic independence.

    Using a simple model with only latitude of distribution as a predictor variable revealed a significant positive relationship with diet breadth. Previous studies, however, have shown that diet breadth is also correlated with butterfly range size, and in turn, that range size may be correlated with latitude of distribution. Including geographical range size in the model also turned out to have a profound effect on the results – to the extent that the relationship between latitude of distribution and diet breadth was effectively reversed.

    We conclude that, at least for this group of butterflies, there is no evidence for a positive correlation between latitude of species distribution and diet breadth when controlling for range size, and that the effect may actually even be reversed.

  • 41.
    Slove, Jessica
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    The Relationship between Diet Breadth and Geographic  Range Size in the Butterfly Subfamily Nymphalinae: A  Study of Global Scale2011In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 6, no 1, p. e16057-Article in journal (Refereed)
    Abstract [en]

    The ‘‘oscillation hypothesis’’ has been proposed as a general explanation for the exceptional diversification of herbivorous insect species. The hypothesis states that speciation rates are elevated through repeated correlated changes – oscillations – in degree of host plant specificity and geographic range. The aim of this study is to test one of the predictions from the oscillation hypothesis: a positive correlation between diet breadth (number of host plants used) and geographic range size, using the globally distributed butterfly subfamily Nymphalinae. Data on diet breadth and global geographic range were collected for 182 Nymphalinae butterflies species and the size of the geographic range was measured using a GIS. We tested both diet breadth and geographic range size for phylogenetic signal to see if species are independent of each other with respect to these characters. As this test gave inconclusive results, data was analysed both using cross-species comparisons and taking phylogeny into account using generalised estimating equations as applied in the APE package in R. Irrespective of which method was used, we found a significant positive correlation between diet breadth and geographic range size. These results are consistent for two different measures of diet breadth and removal of outliers. We conclude that the global range sizes of Nymphalinae butterflies are correlated to diet breadth. That is, butterflies that feed on a large number of host plants tend to have larger geographic ranges than do butterflies that feed on fewer plants. These results lend support for an important step in the oscillation hypothesis of plant-driven diversification, in that it can provide the necessary fuel for future population fragmentation and speciation.

  • 42.
    Söderlind, Lina
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Gamberale-Stille, Gabriella
    Stockholm University, Faculty of Science, Department of Zoology.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology.
    When mother does not know best: Contrasting host plant choice across life stages in individuals of the comma butterflyManuscript (preprint) (Other academic)
    Abstract [en]

    Since host plant choice is often crucial for the fitness of herbivorous insects we investigated if individual variation in such decisions is consistent throughout life. In the comma butterfly, Polygonia c-album, (Nymphalidae, Nymphalini) newly hatched larvae and adult females have been found to rank hosts plants similarly, suggesting that the host plant recognition mechanisms could be preserved through metamorphosis. 

    We measured preference for Urtica dioica relative to Salix cinerea when the plants were encountered by the same individuals in the two different life stages, finding no relationship between the two measurements. This was however found when we instead measured acceptance of a suboptimal host: First instar larvae were placed on the suboptimal S. cinerea, and were scored as to whether they accepted this host or if they instead moved to feed on the generally more preferred host U. dioica. The same individuals were then tested once more as ovipositing females, in a cage setup arranged so that females would encounter the low-ranked hosts S. cinerea and Betula pubescens more often than the high-ranked host U. dioica.

    Individuals that chose to abandon S. cinerea as larvae differed in oviposition behaviour later in life from those that accepted this low-ranked host, but did so by laying a higher proportion eggs on the low-ranked hosts as adults. We interpret this initially unexpected result as a result of possible genetic correlation between female host-plant specificity and larval acceptance for the plant chosen by their mother: Offspring of ‘choosy’ specialist mothers have a strong tendency to remain on their original host, whereas less discriminating generalist mothers beget larvae with lower acceptance for their original plant when it is suboptimal. Ecologically, this presents a further explanation for how a generalist oviposition strategy can be sustained since larval mobility to some extent compensates for poor female choice.

  • 43.
    Söderlind, Lina
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology.
    Effects of sequential diets in the comma butterfly, Polygonia c-album: testing predictions from gene expressionManuscript (preprint) (Other academic)
    Abstract [en]

    Differential gene expression, depending on host plant diet, has been found in the larval mid-gut of the polyphagous butterfly Polygonia c-album. Expression similarities between the hosts elm/sallow and between elm/stinging nettle suggest that there are special patterns of genes for utilizing trees and others for urticalean rosids.

    In order to assess the importance of different genes tailored to host use, we investigated the costs of switching larval diet. Negative effects were expected to be more pronounced when switching between nettle/sallow than between elm/nettle (urticalean rosids) or elm/sallow (trees) since similarities in mid-gut gene expression are fewer.

    However, larvae seemed surprisingly good at adjusting to new environments. Although costs were found after a single switch from sallow to nettle in the 3rd instar as well as on a daily basis the results were not consistent. More surprisingly, we found evidence that costs are involved with a single diet switch to elm. Results suggest rapid physiological adjustment to the new environment, signifying that the induced gene expression is reversible or at least does not seem to inhibit the induction of another gene complex.

  • 44. Trona, Federica
    et al.
    Anfora, Gianfranco
    Balkenius, Anna
    Bengtsson, Marie
    Tasin, Marco
    Knight, Alan
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Witzgall, Peter
    Ignell, Rickard
    Neural coding merges sex and habitat chemosensory signals in an insect herbivore2013In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 280, no 1760, p. 20130267-Article in journal (Refereed)
    Abstract [en]

    Understanding the processing of odour mixtures is a focus in olfaction research. Through a neuroethological approach, we demonstrate that different odour types, sex and habitat cues are coded together in an insect herbivore. Stronger flight attraction of codling moth males, Cydia pomonella, to blends of female sex pheromone and plant odour, compared with single compounds, was corroborated by functional imaging of the olfactory centres in the insect brain, the antennal lobes (ALs). The macroglomerular complex (MGC) in the AL, which is dedicated to pheromone perception, showed an enhanced response to blends of pheromone and plant signals, whereas the response in glomeruli surrounding the MGC was suppressed. Intracellular recordings from AL projection neurons that transmit odour information to higher brain centres, confirmed this synergistic interaction in the MGC. These findings underscore that, in nature, sex pheromone and plant odours are perceived as an ensemble. That mating and habitat cues are coded as blends in the MGC of the AL highlights the dual role of plant signals in habitat selection and in premating sexual communication. It suggests that the MGC is a common target for sexual and natural selection in moths, facilitating ecological speciation.

  • 45.
    Van Dijk, Laura J. A.
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Schäpers, Alexander
    Stockholm University, Faculty of Science, Department of Zoology.
    Gamberale-Stille, Gabriella
    Stockholm University, Faculty of Science, Department of Zoology.
    Carlsson, Mikael A.
    Stockholm University, Faculty of Science, Department of Zoology.
    Experience-dependent mushroom body plasticity in butterflies: consequences of search complexity and host range2017In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 284, no 1866, article id 20171594Article in journal (Refereed)
    Abstract [en]

    An ovipositing insect experiences many sensory challenges during her search for a suitable host plant. These sensory challenges become exceedingly pronounced when host range increases, as larger varieties of sensory inputs have to be perceived and processed in the brain. Neural capacities can be exceeded upon information overload, inflicting costs on oviposition accuracy. One presumed generalist strategy to diminish information overload is the acquisition of a focused search during its lifetime based on experiences within the current environment, a strategy opposed to a more genetically determined focus expected to be seen in relative specialists. We hypothesized that a broader host range is positively correlated with mushroom body (MB) plasticity, a brain structure related to learning and memory. To test this hypothesis, butterflies with diverging host ranges (Polygonia c-album, Aglais io and Aglais urticae) were subjected to differential environmental complexities for oviposition, after which ontogenetic MB calyx volume differences were compared among species. We found that the relative generalist species exhibited remarkable plasticity in ontogenetic MB volumes; MB growth was differentially stimulated based on the complexity of the experienced environment. For relative specialists, MB volume was more canalized. All in all, this study strongly suggests an impact of host range on brain plasticity in Nymphalid butterflies.

  • 46. Wang, Houshuai
    et al.
    Holloway, Jeremy D.
    Janz, Niklas
    Stockholm University, Faculty of Science, Department of Zoology.
    Braga, Mariana P.
    Stockholm University, Faculty of Science, Department of Zoology.
    Wahlberg, Niklas
    Wang, Min
    Nylin, Sören
    Stockholm University, Faculty of Science, Department of Zoology.
    Polyphagy and diversification in tussock moths: Support for the oscillation hypothesis from extreme generalists2017In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 7, no 19, p. 7975-7986Article in journal (Refereed)
    Abstract [en]

    Theory on plasticity driving speciation, as applied to insect-plant interactions (the oscillation hypothesis), predicts more species in clades with higher diversity of host use, all else being equal. Previous support comes mainly from specialized herbivores such as butterflies, and plasticity theory suggests that there may be an upper host range limit where host diversity no longer promotes diversification. The tussock moths (Erebidae: Lymantriinae) are known for extreme levels of polyphagy. We demonstrate that this system is also very different from butterflies in terms of phylogenetic signal for polyphagy and for use of specific host orders. Yet we found support for the generality of the oscillation hypothesis, in that clades with higher diversity of host use were found to contain more species. These clades also consistently contained the most polyphagous single species. Comparing host use in Lymantriinae with related taxa shows that the taxon indeed stands out in terms of the frequency of polyphagous species. Comparative evidence suggests that this is most probably due to its nonfeeding adults, with polyphagy being part of a resulting life history syndrome. Our results indicate that even high levels of plasticity can drive diversification, at least when the levels oscillate over time.

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