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  • 1. Boalt, Elin
    et al.
    Arvanitis, Leena
    Stockholm University, Faculty of Science, Department of Botany.
    Lehtila, Kari
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    The association among herbivory tolerance, ploidy level, and herbivory pressure in cardamine pratensis2010In: Evolutionary Ecology, ISSN 0269-7653, E-ISSN 1573-8477, Vol. 24, no 5, 1101-1113 p.Article in journal (Refereed)
    Abstract [en]

    We tested whether differences in ploidy level and previous exposure to herbivory can affect plant tolerance to herbivory. We conducted a common garden experiment with 12 populations of two ploidy levels of the perennial herb Cardamine pratensis (five populations of tetraploid ssp. pratensis and seven populations of octoploid ssp. paludosa). Earlier studies have shown that attack rates by the main herbivore, the orange tip butterfly Anthocharis cardamines, are lower in populations of octoploids than in populations of tetraploids, and vary among populations. In the common garden experiment, a combination of natural and artificial damage significantly reduced seed and flower production. We measured tolerance based on four plant-performance metrics: survival, growth, seed production and clonal reproduction. For three of these measurements, tolerance of damage did not differ between ploidy levels. For clonal reproduction, the octoploids had a higher tolerance than the tetraploids, although they experience lower herbivore attack rates in natural populations. Populations from sites with high levels of herbivory had higher tolerance, measured by seed production, than populations with low levels of herbivory. We did not detect any significant costs of tolerance. We conclude that high intensity of herbivory has selected for high tolerance measured by seed production in C. pratensis.

  • 2. Esperk, Toomas
    et al.
    Stefanescu, Constanti
    Teder, Tiit
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Kaasik, Ants
    Tammaru, Toomas
    Distinguishing between anticipatory and responsive plasticity in a seasonally polyphenic butterfly2013In: Evolutionary Ecology, ISSN 0269-7653, E-ISSN 1573-8477, Vol. 27, no 2, 315-332 p.Article in journal (Refereed)
    Abstract [en]

    Seasonal generations of short-lived organisms often differ in their morphological, behavioural and life history traits, including body size. These differences may be either due to immediate effects of seasonally variable environment on organisms (responsive plasticity) or rely on presumably adaptive responses of organisms to cues signalizing forthcoming seasonal changes (anticipatory plasticity). When directly developing individuals of insects are larger than their overwintering conspecifics, the between-generation differences are typically ascribed to responsive plasticity in larval growth. We tested this hypothesis using the papilionid butterly Iphiclides podalirius as a model species. In laboratory experiments, we demonstrated that seasonal differences in food quality could not explain the observed size difference. Similarly, the size differences are not likely to be explained by the immediate effects of ambient temperature and photoperiod on larval growth. The qualitative pattern of natural size differences between the directly developing and diapausing butterflies could be reproduced in the laboratory as a response to photoperiod, indicating anticipatory character of the response. Directly developing and diapausing individuals followed an identical growth trajectory until the end of the last larval instar, with size differences appearing just a few days before pupation. Taken together, various lines of evidence suggest that between-generation size differences in I. podalirius are not caused by immediate effects of environmental factors on larval growth. Instead, these differences rather represent anticipatory plasticity and are thus likely to have an adaptive explanation. It remains currently unclear, whether the seasonal differences in adult size per se are adaptive, or if they constitute co-product of processes related to the diapause. Our study shows that it may be feasible to distinguish between different types of plasticity on the basis of empirical data even if fitness cannot be directly measured, and contributes to the emerging view about the predominantly adaptive nature of seasonal polyphenisms in insects.

  • 3.
    Gamberale-Stille, Gabriella
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Johansen, Aleksandra I.
    Stockholm University, Faculty of Science, Department of Zoology.
    Tullberg, Birgitta S.
    Stockholm University, Faculty of Science, Department of Zoology.
    Change in protective coloration in the striated shieldbug Graphosoma lineatum (Heteroptera: Pentatomidae): predator avoidance and generalization among different  life stages2010In: Evolutionary Ecology, ISSN 0269-7653, E-ISSN 1573-8477, Vol. 24, no 2, 423-432 p.Article in journal (Refereed)
    Abstract [en]

    There are two major forms of protective coloration, camouflage and warning coloration, which often entail different colour pattern characteristics. Some species change strategy between or within life stages and one such example is the striated shieldbug, Graphosoma lineatum. The larvae and the pale brownish-and-black striated pre-diapause adults are more cryptic in the late summer environment than is the red-and black striation that the adults change to after diapause in spring. Here we investigate if the more cryptic pre-diapause adult and larval coloration may affect the aposematic function of the coloration as compared to the red adult form. In a series of trials we presented fifth instar larvae, pale or red adults to shieldbug-naïve domestic chicks, Gallus gallus domesticus, to investigate the birds’ initial wariness, avoidance learning, and generalization between the three prey types. The naïve chicks found the red adults most aversive followed by pale adults, and they found the larvae the least aversive. The birds did not find the larvae unpalatable and did not learn to avoid them, while they learned to avoid the two adult forms and then to a similar degree. Birds generalized asymmetrically between life stages, positively from larvae to adults and negatively from adults to larvae. We conclude that the lower conspicuousness in the pale forms of G. lineatum may entail a reduced aposematic function, namely a reduced initial wariness in inexperienced birds. The maintenance of the colour polymorphism is discussed

  • 4.
    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, 289-302 p.Article 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.

  • 5. Kolb, Annette
    et al.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Environmental context drives seed predator-mediated selection on a floral display trait2010In: Evolutionary Ecology, ISSN 0269-7653, E-ISSN 1573-8477, Vol. 24, no 2, 433-445 p.Article in journal (Refereed)
    Abstract [en]

    Linking trait selection to environmental context is necessary to move beyond the simple recognition that selection is spatially variable and to understand what ultimately drives this variation. Natural selection acts through differences among individuals in lifetime fitness and information about effects on fitness components is therefore often not sufficient to gain such an understanding. We investigated how environmental context influenced intensity of seed predation, flower abortion and selection on floral display traits in 44-52 populations of the perennial herb Primula veris over 2 years. Phenotypic selection on both inflorescence height and flower number varied among populations and was mediated partly by pre-dispersal seed predation and flower abortion in one of the years. Among-population variation in selection on inflorescence height, but not flower number, was linked to variation in canopy cover via its effects on seed predation. Lifetime fitness was less sensitive to seed predator damage in shaded environments but estimates of selection based on lifetime fitness agreed qualitatively with those based on seed output. Our results demonstrate that seed predators constitute an important link between environmental conditions and trait evolution in plants, and that selection on plant traits by seed predators can depend on environmental context.

  • 6.
    Kotrschal, Alexander
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Deacon, Amy E.
    Magurran, Anne E.
    Kolm, Niclas
    Stockholm University, Faculty of Science, Department of Zoology.
    Predation pressure shapes brain anatomy in the wild2017In: Evolutionary Ecology, ISSN 0269-7653, E-ISSN 1573-8477, Vol. 31, no 5, 619-633 p.Article in journal (Refereed)
    Abstract [en]

    There is remarkable diversity in brain anatomy among vertebrates and evidence is accumulating that predatory interactions are crucially important for this diversity. To test this hypothesis, we collected female guppies (Poecilia reticulata) from 16 wild populations and related their brain anatomy to several aspects of predation pressure in this ecosystem, such as the biomass of the four major predators of guppies (one prawn and three fish species), and predator diversity (number of predatory fish species in each site). We found that populations from localities with higher prawn biomass had relatively larger telencephalon size as well as larger brains. Optic tectum size was positively associated with one of the fish predator's biomass and with overall predator diversity. However, both olfactory bulb and hypothalamus size were negatively associated with the biomass of another of the fish predators. Hence, while fish predator occurrence is associated with variation in brain anatomy, prawn occurrence is associated with variation in brain size. Our results suggest that cognitive challenges posed by local differences in predator communities may lead to changes in prey brain anatomy in the wild.

  • 7. Kotrschal, Alexander
    et al.
    Trombley, Susanne
    Rogell, Björn
    Brännström, Ioana
    Foconi, Eric
    Schmitz, Monika
    Kolm, Niclas
    Stockholm University, Faculty of Science, Department of Zoology. Uppsala University, Sweden.
    The mating brain: early maturing sneaker males maintain investment into the brain also under fast body growth in Atlantic salmon (Salmo salar)2014In: Evolutionary Ecology, ISSN 0269-7653, E-ISSN 1573-8477, Vol. 28, no 6, 1043-1055 p.Article in journal (Refereed)
    Abstract [en]

    It has been suggested that mating behaviours require high levels of cognitive ability. However, since investment into mating and the brain both are costly features, their relationship is likely characterized by energetic trade-offs. Empirical data on the subject remains equivocal. We investigated if early sexual maturation was associated with brain development in Atlantic salmon (Salmo salar), in which males can either stay in the river and sexually mature at a small size (sneaker males) or migrate to the sea and delay sexual maturation until they have grown much larger (anadromous males). Specifically, we tested how sexual maturation may induce plastic changes in brain development by rearing juveniles on either natural or ad libitum feeding levels. After their first season we compared brain size and brain region volumes across both types of male mating tactics and females. Body growth increased greatly across both male mating tactics and females during ad libitum feeding as compared to natural feeding levels. However, despite similar relative increases in body size, early maturing sneaker males maintained larger relative brain size during ad libitum feeding levels as compared to anadromous males and females. We also detected several differences in the relative size of separate brain regions across feeding treatments, sexes and mating strategies. For instance, the relative size of the cognitive centre of the brain, the telencephalon, was largest in sneaker males. Our data support that a large relative brain size is maintained in individuals that start reproduction early also during fast body growth. We propose that the cognitive demands during complex mating behaviours maintain a high level of investment into brain development in reproducing individuals.

  • 8.
    Lehmann, Philipp
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. University of Jyväskylä, Finland.
    Lyytinen, Anne
    Piiroinen, Saija
    Lindström, Leena
    Latitudinal differences in diapause related photoperiodic responses of European Colorado potato beetles (Leptinotarsa decemlineata)2015In: Evolutionary Ecology, ISSN 0269-7653, E-ISSN 1573-8477, Vol. 29, no 2, 269-282 p.Article in journal (Refereed)
    Abstract [en]

    Many organisms use photoperiodic cues to assess seasonal progression and pace their phenology. As photoperiod correlates with latitude, range expansions in seasonal environments may require re-synchronization of phenology and life-history traits with novel season length. Adaptive resynchronization takes time, and hence might be one factor explaining why range expansion to higher latitudes often is slow. Studies investigating latitudinal clines in photoperiodic traits often focus on species or populations which are well established. However, studying organisms which are in the process of expanding their range can provide valuable information on the evolutionary ecological mechanisms driving the adaptive synchronization to seasonal environments. The Colorado potato beetle, Leptinotarsa decemlineata, is a pest of potato, which rapidly has spread towards higher latitudes. We studied whether beetles from six European populations along a latitudinal axis are synchronized with their local photoperiodic environmental conditions. Variation in critical photoperiod (when 50 % of individuals make the decision to overwinter), diapause incidence, burrowing age for diapause and resurfacing behaviour were investigated by maintaining beetles under six photoperiods. The beetles showed a clear latitudinal pattern in diapause incidence and burrowing age for diapause but not in critical photoperiod. Resurfacing behaviour of burrowed beetles increased with the length of the photoperiod, which through unsynchronized overwintering behaviour could lead to high overwintering mortality. Thus, while synchronization of diapause preparation with local photoperiodic conditions can be one reason explaining the success of L. decemlineata in expanding to higher latitudes, further northward range expansion could be constrained by inherent difficulties to initiate overwintering under very long photoperiods.

  • 9.
    Leimar, Olof
    Stockholm University, Faculty of Science, Department of Zoology.
    Environmental and genetic cues in the evolution of phenotypic polymorphism2009In: Evolutionary Ecology, ISSN 0269-7653, E-ISSN 1573-8477, Vol. 23, 125-135 p.Article in journal (Refereed)
    Abstract [en]

    Phenotypic polymorphism is a consequence of developmental plasticity, in which the trajectories of developing organisms diverge under the influence of cues. Environmental and genetic phenotype determination are the two main categories of polymorphic development. Even though both may evolve as a response to varied environments, they are traditionally regarded as fundamentally distinct phenomena. They can however be joined into a single framework that emphasizes the parallel roles of environmental and genetic cues in phenotype determination. First, from the point of view of immediate causation, it is common that phenotypic variants can be induced either by environmental or by allelic variation, and this is referred to as gene-environment interchangeability. Second, from the point of view of adaptation, genetic cues in the form of allelic variation at polymorphic loci can play similar roles as environmental cues in providing information to the developmental system about coming selective conditions. Both types of cues can help a developing organism to fit its phenotype to selective circumstances. This perspective of information in environmental and genetic cues can produce testable hypotheses about phenotype determination, and can thus increase our understanding of the evolution of phenotypic polymorphism.

  • 10.
    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, 137-146 p.Article 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.

  • 11.
    Nylin, Sören
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Nygren, Georg H.
    Stockholm University, Faculty of Science, Department of Zoology.
    Söderlind, Lina
    Stockholm University, Faculty of Science, Department of Zoology.
    Stefanescu, Constanti
    Museu de Granollers Ciencies Naturals, Spanien.
    Geographical variation in host plant utilization in the comma butterfly: the roles of time constraints and plant phenology2009In: Evolutionary Ecology, ISSN 0269-7653, E-ISSN 1573-8477, Vol. 23, 807-825 p.Article in journal (Refereed)
    Abstract [en]

    What is the role of time-constraints in determining geographical variation in the resource use of organisms? One hypothesis concerning phytophagous insects predicts a local narrowing of host plant range at localities where a short development time is important (because an additional generation per season is only just possible), with increased specialization on host plants permitting fast development. To test this hypothesis, populations of the polyphagous comma butterfly (Nymphalidae: Polygonia c-album) from five European areas (localities in Norway, Sweden, England, Belgium and Spain) were sampled and the preferences of laboratory-reared female butterflies were investigated, by a choice test between Salix caprea and the fastest host Urtica dioica. The results suggest that females of both of two northern univoltine populations (time-stressed from Norway and time-relaxed from Sweden) accept the slow host S. caprea to a higher degree than females of more southern populations with partial additional generations (time-stressed). We thus found partial support for the tested hypothesis, but also conflicting results that cast doubt on its broad generality. Moreover, a split-brood investigation on Swedish stock demonstrated that larval performance is similar on S. caprea and U. dioica early in the summer, but that later in the season S. caprea is a much inferior host. This is reflected by a seasonal trend towards specialization on U. dioica and also provides a simpler explanation than the time-constraints theory for avoidance of S. caprea (and other woody hosts) in areas with two or more generations of insects per year, illustrating the importance of plant phenology as a constraint on resource use in phytophagous insects. Absolute and relative larval performance on the two hosts varied little among populations across Europe, but lower survival on S. caprea in the populations most specialized on U. dioica and related plants may be indicative of performance trade-offs.

  • 12. Toräng, Per
    et al.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Ågren, Jon
    Habitat quality and among-population differentiation in reproductive effort and flowering phenology in the perennial herb Primula farinosa2009In: Evolutionary Ecology, ISSN 0269-7653, E-ISSN 1573-8477, Vol. 24, no 4, 715-729 p.Article in journal (Refereed)
    Abstract [en]

    In heterogeneous environments, selection on life-history traits and flowering time may vary considerably among populations because of differences in the extent to which mortality is related to age or size, and because of differences in the seasonal patterns of resource availability and intensity of biotic interactions. Spatial variation in optimal reproductive effort and flowering time may result in the evolution of genetic differences in life-history traits, but also in the evolution of adaptive phenotypic plasticity. The perennial herb Primula farinosa occurs at sites that differ widely in soil depth and therefore in water-holding capacity, vegetation cover, and frost-induced soil movement in winter. We used data from eight natural populations and a common-garden experiment to test the predictions that reproductive allocation is negatively correlated with soil depth while age at first reproduction and first flowering date among reproductive individuals are positively correlated with soil depth. In the common-garden experiment, maternal families collected in the field were grown from seed and monitored for 5 years. In the field, reproductive effort (number of flowers in relation to rosette area) varied among populations and was negatively related to soil depth. In the common-garden experiment, among-population differences in age at first reproduction, and reproductive effort were statistically significant, but relatively small and not correlated with soil depth at the site of origin. Flowering time varied considerably among populations, but was not related to soil depth at the site of origin. Taken together, the results suggest that among-population variation in reproductive effort observed in the field largely reflects phenotypic plasticity. They further suggest that among-population differentiation in flowering time cannot be attributed to variation in environmental factors correlated with soil depth.

  • 13.
    Tsuboi, Masahito
    et al.
    Uppsala universitet, Zooekologi.
    Gonzalez-Voyer, Alejandro
    Uppsala universitet, Zooekologi.
    Höglund, Jacob
    Uppsala universitet, Populationsbiologi och naturvårdsbiologi.
    Kolm, Niclas
    Uppsala universitet, Zooekologi.
    Ecology and mating competition influence sexual dimorphism in Tanganyikan cichlids2012In: Evolutionary Ecology, ISSN 0269-7653, E-ISSN 1573-8477, Vol. 26, no 1, 171-185 p.Article in journal (Refereed)
    Abstract [en]

    Sexual selection contributes strongly to the evolution of sexual dimorphism among animal taxa. However, recent comparative analyses have shown that evolution of sexual dimorphism can be influenced by extrinsic factors like mating system and environment, and also that different types of sexual dimorphism may present distinct evolutionary pathways. Investigating the co-variation among different types of sexual dimorphism and their association with environmental factors can therefore provide important information about the mechanisms generating variation in sexual dimorphism among contemporary species. Using phylogenetic comparative analyses comparing 49 species of Tanganyikan cichlid fishes, we first investigated the pairwise relationship between three types of sexual dimorphism [size dimorphism (SSD), colour dimorphism (COD) and shape dimorphism (SHD)] and how they were related to the strength of pre- and post-copulatory sexual selection. We then investigated the influence of ecological features on sexual dimorphism. Our results showed that although SSD was associated with the overall strength of sexual selection it was not related to other types of sexual dimorphism. Also, SSD co-varied with female size and spawning habitat, suggesting a role for female adaptations to spawn in small crevices and shells influencing SSD in this group. Further, COD and SHD were positively associated and both show positive relationships with the strength of sexual selection. Finally, the level of COD and SHD was related to habitat complexity. Our results thus highlight distinct evolutionary pathways for different types of sexual dimorphism and further that ecological factors have influenced the evolution of sexual dimorphism in Tanganyikan cichlid fishes.

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