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  • 1.
    Berger, D.
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Friberg, M.
    Olofsson, M.
    Wiklund, C.
    Large females lose more: sexual conflicts reduce female fecundity and directional selection on body size in the butterfly Leptidea sinapis.Manuscript (Other (popular science, discussion, etc.))
  • 2.
    Berger, David
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Friberg, Magne
    Stockholm University, Faculty of Science, Department of Zoology.
    Gotthard, Karl
    Stockholm University, Faculty of Science, Department of Zoology.
    Divergence and ontogenetic coupling of larval behaviour and thermal reaction norms in three closely related butterflies2011In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 278, no 1703, p. 313-320Article in journal (Refereed)
    Abstract [en]

    Genetic trade-offs such as between generalist-specialist strategies can be masked by changes in compensatory processes involving energy allocation and acquisition which regulation depends on the state of the individual and its ecological surroundings. Failure to account for such state dependence may thus lead to misconceptions about the trade-off structure and nature of constraints governing reaction norm evolution. Using three closely related butterflies, we first show that foraging behaviours differ between species and change remarkably throughout ontogeny causing corresponding differences in the thermal niches experienced by the foraging larvae. We further predicted that thermal reaction norms for larval growth rate would show state-dependent variation throughout development as a result of selection for optimizing feeding strategies in the respective foraging niches of young and old larvae. We found substantial developmental plasticity in reaction norms that was species-specific and reflected the different ontogenetic niche shifts. Any conclusions regarding constraints on performance curves or species-differentiation in thermal physiology depend on when reaction norms were measured. This demonstrates that standardized estimates at single points in development, or in general, allow variation in only one ecological dimension, may sometimes provide incomplete information on reaction norm constraints.

  • 3.
    Berger, David
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. Uppsala University, Sweden.
    Olofsson, Martin
    Stockholm University, Faculty of Science, Department of Zoology.
    Friberg, Magne
    Stockholm University, Faculty of Science, Department of Zoology. University of California Santa Cruz, USA.
    Karlsson, Bengt
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Gotthard, Karl
    Stockholm University, Faculty of Science, Department of Zoology.
    Intraspecific variation in body size and the rate of reproduction in female insects- adaptive allometry or biophysical constraint?2012In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 81, no 6, p. 1244-1258Article in journal (Refereed)
    Abstract [en]

    1. A high rate of reproduction may be costly if ecological factors limit immediate reproductive output as a fast metabolism compromises own future survival. Individuals with more reserves need more time and opportunity to realize their reproductive potential. Theory therefore predicts that the reproductive rate, defined as the investment in early reproduction in proportion to total potential, should decrease with body size within species. 2. However, metabolic constraints on body size- and temperature-dependent biological rates may impede biophysical adaptation. Furthermore, the sequential manner resources that are allocated to somatic vs. reproductive tissue during ontogeny may, when juveniles develop in unpredictable environments, further contribute to non-adaptive variation in adult reproductive rates. 3. With a model on female egg laying in insects, we demonstrate how variation in body reserves is predicted to affect reproductive rate under different ecological scenarios. Small females always have higher reproductive rates but shorter lifespans. However, incorporation of female host selectivity leads to more similar reproductive rates among female size classes, and oviposition behaviour is predicted to co-evolve with reproductive rate, resulting in small females being more selective in their choice and gaining relatively more from it. 4. We fed simulations with data on the butterfly Pararge aegeria to compare model predictions with reproductive rates of wild butterflies. However, simulated reproductive allometry was a poor predictor of that observed. Instead, reproductive rates were better explained as a product of metabolic constraints on rates of egg maturation, and an empirically derived positive allometry between reproductive potential and size. However, fitness is insensitive to moderate deviations in reproductive rate when oviposition behaviour is allowed to co-evolve in the simulations, suggesting that behavioural compensation may mitigate putative metabolic and developmental constraints. 5. More work is needed to understand how physiology and development together with compensatory behaviours interact in shaping reproductive allometry. Empirical studies should evaluate adaptive hypotheses against proper null hypotheses, including prediction from metabolic theory, preferentially by studying reproductive physiology in combination with behaviour. Conversely, inferences of constraint explanations on reproductive rates must take into consideration that adaptive scenarios may predict similar allometric exponents.

  • 4.
    Berger, David
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Olofsson, Martin
    Stockholm University, Faculty of Science, Department of Zoology.
    Gotthard, Karl
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Friberg, Magne
    Stockholm University, Faculty of Science, Department of Zoology.
    Ecological Constraints on Female Fitness in a Phytophagous Insect2012In: American Naturalist, ISSN 0003-0147, E-ISSN 1537-5323, Vol. 180, no 4, p. 464-480Article in journal (Refereed)
    Abstract [en]

    Although understanding female reproduction is crucial for population demography, determining how and to what relative extent it is constrained by different ecological factors is complicated by difficulties in studying the links between individual behavior, life history, and fitness in nature. We present data on females in a natural population of the butterfly Leptidea sinapis. These data were combined with climate records and laboratory estimates of life-history parameters to predict the relative impact of different ecological constraints on female fitness in the wild. Using simulation models, we partitioned effects of male courtship, host plant availability, and temperature on female fitness. Results of these models indicate that temperature is the most constraining factor on female fitness, followed by host plant availability; the short-term negative effects of male courtship that were detected in the field study were less important in models predicting female reproductive success over the entire life span. In the simulations, females with more reproductive reserves were more limited by the ecological variables. Reproductive physiology and egg-laying behavior were therefore predicted to be co-optimized but reach different optima for females of different body sizes; this prediction is supported by the empirical data. This study thus highlights the need for studying behavioral and life-history variation in orchestration to achieve a more complete picture of both demographic and evolutionary processes in naturally variable and unpredictable environments.

  • 5.
    Dinca, Vlad
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Lukhtanov, V. A.
    Kodandaramaiah, U.
    Norén, Karin
    Stockholm University, Faculty of Science, Department of Zoology.
    Dapporto, L.
    Wahlberg, N.
    Vila, R.
    Friberg, Mange
    Stockholm University, Faculty of Science, Department of Zoology.
    Reproductive isolation and patterns of genetic differentiation in a cryptic butterfly species complex2013In: Journal of Evolutionary Biology, ISSN 1010-061X, E-ISSN 1420-9101, Vol. 26, no 10, p. 2095-2106Article in journal (Refereed)
    Abstract [en]

    Molecular studies of natural populations are often designed to detect and categorize hidden layers of cryptic diversity, and an emerging pattern suggests that cryptic species are more common and more widely distributed than previously thought. However, these studies are often decoupled from ecological and behavioural studies of species divergence. Thus, the mechanisms by which the cryptic diversity is distributed and maintained across large spatial scales are often unknown. In 1988, it was discovered that the common Eurasian Wood White butterfly consisted of two species (Leptidea sinapis and Leptidea reali), and the pair became an emerging model for the study of speciation and chromosomal evolution. In 2011, the existence of a third cryptic species (Leptidea juvernica) was proposed. This unexpected discovery raises questions about the mechanisms preventing gene flow and about the potential existence of additional species hidden in the complex. Here, we compare patterns of genetic divergence across western Eurasia in an extensive data set of mitochondrial and nuclear DNA sequences with behavioural data on inter- and intraspecific reproductive isolation in courtship experiments. We show that three species exist in accordance with both the phylogenetic and biological species concepts and that additional hidden diversity is unlikely to occur in Europe. The Leptidea species are now the best studied cryptic complex of butterflies in Europe and a promising model system for understanding the formation of cryptic species and the roles of local processes, colonization patterns and heterospecific interactions for ecological and evolutionary divergence.

  • 6.
    Friberg, Magne
    Stockholm University, Faculty of Science, Department of Zoology.
    A difference in pupal morphology between the sibling species Leptidea sinapis and L. reali (Pieridae)2007In: Nota lepidopterologica, ISSN 0342-7536, Vol. 30, no 1, p. 61-64Article in journal (Refereed)
    Abstract [en]

    The sister species Leptidea sinapis and L. reali are virtually identical and species identification has so far only been possible through DNA-sequencing or genital preparation. Here, I show an interspecific difference in pupal morphology. The pupal antennae of L. sinapis are white with a well-defined longitudinal pink line in the middle, while those of L. reali are predominantly pink with only scattered white pigments close to the margin on both sides.

  • 7.
    Friberg, Magne
    Stockholm University, Faculty of Science, Department of Zoology. Zoologisk ekologi.
    Female choice, voltinism and ecological pleiotropy - causes and consequences of the species divergence between Leptidea sinapis and L.reali.2006Licentiate thesis, monograph (Other academic)
  • 8.
    Friberg, Magne
    Stockholm University, Faculty of Science, Department of Zoology.
    The evolutionary ecology of niche separation: Studies on the sympatric butterflies Leptidea sinapis and Leptidea reali2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Studies of ecology and evolution have become largely integrated, and increasing attention is paid to the role of ecology for speciation and post speciation divergence. In this thesis I have applied an in-depth approach studying the ecology of a butterfly species pair; the morphologically virtually identical sister-species, the Wood white (Leptidea sinapis) and Reál’s wood white (Leptidea reali). PAPER I showed a quite deep between-species division in sequence data from mitochondrial DNA. The reuniting in secondary contact zones might in contrast be quite recent, as males of L. sinapis and L. reali cannot distinguish between con- and heterospecific females (PAPER II) and since the between-species niche separation is incomplete (PAPER III, IV, V). Furthermore, the two species have partitioned their niches in different directions in different European regions as the two species shift habitat generalist and specialist roles throughout their joint distribution (PAPER III). However, the local niche partitioning has resulted in species-specific adaptations in terms of propensity to enter diapause (PAPER III, V, VI), host plant acceptance (PAPER V), and in ability to use host plant as cue for the decision to enter diapause or direct development (PAPER VI). The habitat separation is decoupled from host plant preference, at least in south central Sweden (PAPER IV), which implies that selection for niche partitioning has acted on habitat preferences directly and not via divergent selection on host plant preference. Finally, there is a high cost of appearing at a site where the other species is in the majority as much time (PAPER VII) and energy (PAPER II) are devoted to court heterospecific females or being courted by heterospecific males (PAPER VII). Hence, selection likely favours habitat specialisation in the rarest species in each region, and the direction of niche separation might simply be decided by which species that reached an area first. The species that first colonises an area would then most likely become a generalist filling up all suitable habitats, whereas the second invader might be forced to specialise, as the cost of being rare is too large everywhere but in the core population. This thesis highlights the role of ecology, and especially of local processes, for post-speciation selection and character displacement.

     

  • 9.
    Friberg, Magne
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Aalberg Haugen, Inger M.
    Stockholm University, Faculty of Science, Department of Zoology.
    Dahlerus, Josefin
    Stockholm University, Faculty of Science, Department of Zoology.
    Gotthard, Karl
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Asymmetric life-history decision-making in butterfly larvae2011In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 165, no 2, p. 301-310Article in journal (Refereed)
    Abstract [en]

    In temperate environments, insects appearing in several generations in the growth season typically have to decide during the larval period whether to develop into adulthood, or to postpone adult emergence until next season by entering a species-specific diapause stage. This decision is typically guided by environmental cues experienced during development. An early decision makes it possible to adjust growth rate, which would allow the growing larva to respond to time stress involved in direct development, whereas a last-minute decision would instead allow the larva to use up-to-date information about which developmental pathway is the most favourable under the current circumstances. We study the timing of the larval pathway decision-making between entering pupal winter diapause and direct development in three distantly related butterflies (Pieris napi, Araschnia levana and Pararge aegeria). We pinpoint the timing of the larval diapause decision by transferring larvae from first to last instars from long daylength (inducing direct development) to short daylength conditions (inducing diapause), and vice versa. Results show that the pathway decision is typically made in the late instars in all three species, and that the ability to switch developmental pathway late in juvenile life is conditional; larvae more freely switched from diapause to direct development than in the opposite direction. We contend that this asymmetry is influenced by the additional physiological preparations needed to survive the long and cold winter period, and that the reluctance to make a late decision to enter diapause has the potential to be a general trait among temperate insects.

  • 10.
    Friberg, Magne
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. Zoologisk ekologi.
    Bergman, Martin
    Stockholm University, Faculty of Science, Department of Zoology. Zoologisk ekologi.
    Wahlberg, Niklas
    Kullberg, Jakkoo
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology. Zoologisk ekologi.
    Niche separation in space and time between two sympatric sister species—a case of ecological pleiotropy2008In: Evolutionary Ecology, ISSN 0269-7653Article in journal (Refereed)
    Abstract [en]

    Abstract We investigate the niche separation in space and time between the Palearctic sister species Leptidea sinapis and L. reali (Lepidoptera, Pieridae) in central Sweden. Using field sampling, we show that L. reali is a habitat specialist confined to meadows, whereas L. sinapis is a habitat generalist also inhabiting forests. This difference in habitat utilization was corroborated by experimental release of laboratory-reared L. sinapis and L. reali in two adjacent forest and meadow habitats during their natural flight period; virtually all recaptured L. reali that were released in the forest were later caught in the meadow, whereas L. sinapis shifted equally often from meadow to forest as in the opposite direction. In the field, both species fly in May–June, but L. reali appears on average a week earlier in spring and has a substantial second generation in July, whereas L. sinapis is practically univoltine. When overwintered pupae were incubated under identical conditions in the laboratory, females did, however, not differ in phenology, and L. sinapis males actually emerged earlier than L. reali males. When larvae were reared at 23°C on the host plant Lotus corniculatus at a range of daylengths, both species produced a substantial proportion of directly developing individuals at an 18.5 h daylength or longer. When reared at 23°C and a 22 h daylength, L. reali showed an overall higher propensity to develop directly than L. sinapis on plant species originating from both the meadow and the forest habitat. Both Leptidea species showed a lower propensity to enter direct development on forest associated plants than on meadow associated plants. Hence, we suggest that the difference in phenology and voltinism between L. sinapis and L. reali is largely the result of environmentally implemented ecological pleiotropic effects caused by the between-species difference in habitat preference.

  • 11.
    Friberg, Magne
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Dahlerus, Josefin
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Strategic larval decision-making in a bivoltine butterfly2012In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 169, no 3, p. 623-635Article in journal (Refereed)
    Abstract [en]

    In temperate areas, insect larvae must decide between entering winter diapause or developing directly and reproducing in the same season. Long daylength and high temperature promote direct development, which is generally associated with a higher growth rate. In this work, we investigated whether the larval pathway decision precedes the adjustment of growth rate (state-independent), or whether the pathway decision is conditional on the individual's growth rate (state-dependent), in the butterfly Pieris napi. This species typically makes the pathway decision in the penultimate instar. We measured growth rate throughout larval development under two daylengths: slightly shorter and slightly longer than the critical daylength. Results indicate that the pathway decision can be both state-independent and state-dependent; under the shorter daylength condition, most larvae entered diapause, and direct development was chosen exclusively by a small subset of larvae showing the highest growth rates already in the early instars; under the longer daylength condition, most larvae developed directly, and the diapause pathway was chosen exclusively by a small subset of slow-growing individuals. Among the remainder, the choice of pathway was independent of the early growth rate; larvae entering diapause under the short daylength grew as fast as or faster than the direct developers under the longer daylength in the early instars, whereas the direct developers grew faster than the diapausers only in the ultimate instar. Hence, the pathway decision was state-dependent in a subset with a very high or very low growth rate, whereas the decision was state-independent in the majority of the larvae, which made the growth rate adjustment downstream from the pathway decision.

  • 12.
    Friberg, Magne
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Karlsson, Bengt
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Life-history polyphenism in the Map butterfly (Araschnia levana): developmental constraints versus season-specific adaptations2010In: Evolutionary Ecology Research, ISSN 1522-0613, E-ISSN 1937-3791, Vol. 12, p. 603-615Article in journal (Refereed)
    Abstract [en]

    Hypothesis: Different generations of a seasonally polyphenic butterfly allocate their resources differently between dispersal ability and reproduction to fit the environmental circumstances specific to the seasonal environment of each generation.

    Organism: Map butterfly (Araschnia levana).

    Site of experiments: The Department of Zoology/Tovetorp Research Station, Stockholm University.

    Methods: We estimated fecundity by assessing the amount of the limiting resource nitrogen that individuals of each generation allocated to their abdomens. We studied dispersal ability by assessing thorax nitrogen content, and by studying flight ability of both generations in a suite of temperatures.

    Results: Individuals of the summer generation performed longer sustained flights than individuals of the spring generation in all temperatures except the warmest treatment. In males, abdomen nitrogen content was poorly correlated with thorax nitrogen content. Thus males do not need to trade off nitrogen between the tissues. However, female thorax and abdomen nitrogen contents were strongly positively correlated, and although summer females were better flyers than spring females, they still allocated disproportionately more nitrogen to the reproductive tissue in the abdomen. We conclude that the divergent allocation patterns between different Map butterfly generations are better understood in terms of developmental constraints acting on spring butterflies, rather than by season-specific adaptations.

  • 13.
    Friberg, Magne
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Kodandaramaiah, Ullasa
    Stockholm University, Faculty of Science, Department of Zoology.
    Norén, Karin
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Wahlberg, Niklas
    Department of Biology, University of Turku.
    Genetic differentiation and phylogeographic patterns in European populations of Leptidea sinapis and L. realiManuscript (preprint) (Refereed)
    Abstract [en]

    The direction of a coevolutionary interaction can differ between local populations as in the butterflies Leptidea sinapis and L. reali. The morphologically virtually identical sister-species have partitioned their niches differently in different parts of their distribution by shifting habitat specialist and generalist roles between different sympatric areas. Hence, a species that is a generalist in some areas can be a local specialist in others, and vice versa. We have sequenced the mitochondrial COI gene from specimens collected across Europe in order to (i) describe the between-species variation over a large area, (ii) identify possible glacial refugia and re-colonisation routes to obtain a phylogeographic hypothesis for explaining the geographic mosaic of niche separation and (iii) apply a population genetic approach to determine the level of intraspecific genetic differentiation. The results show evidence for species distinctiveness throughout Europe. Only small variation was found in L. reali, whereas the haplotype network of L. sinapis showed a deep division into two haplotype families of which one was restricted to Spain and the other was widespread over the continent (including Spain). The widespread haplotype family was divided into two common variants, one eastern and one western, each being surrounded by rare haplotypes. The both deep and shallow genetic differentiation implies that L. sinapis might have been divided into different refugia during several glaciations. Both species showed significant genetic differentiation in pairwise ФST, and as habitat generalist populations could differ significantly from other habitat generalist populations but not from habitat specialist populations, we conclude that this study supports that the geographic mosaic of niche separation is caused by local processes rather than common ancestry of local habitat generalists or specialists within each species

  • 14.
    Friberg, Magne
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. Uppsala universitet.
    Leimar, Olof
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Heterospecific courtship, minority effects and niche separation between cryptic butterfly species2013In: Journal of Evolutionary Biology, ISSN 1010-061X, E-ISSN 1420-9101, Vol. 26, no 5, p. 971-979Article in journal (Refereed)
    Abstract [en]

    Species interacting in varied ecological conditions often evolve in different directions in different local populations. The butterflies of the cryptic Leptidea complex are sympatrically distributed in different combinations across their Eurasian range. Interestingly, the same species is a habitat generalist in some regions and a habitat specialist in others, where a sibling species has the habitat generalist role. Previous studies suggest that this geographically variable niche divergence is generated by local processes in different contact zones. By varying the absolute and relative densities of Leptidea sinapis and Leptidea juvernica in large outdoor cages, we show that female mating success is unaffected by conspecific density, but strongly negatively affected by the density of the other species. Whereas 80% of the females mated when a conspecific couple was alone in a cage, less than 10% mated when the single couple shared the cage with five pairs of the other species. The heterospecific courtships can thus affect the population fitness, and for the species in the local minority, the suitability of a habitat is likely to depend on the presence or absence of the locally interacting species. If the local relative abundance of the different species depends on the colonization order, priority effects might determine the ecological roles of interacting species in this system.

  • 15.
    Friberg, Magne
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Olofsson, Martin
    Stockholm University, Faculty of Science, Department of Zoology.
    Berger, David
    Stockholm University, Faculty of Science, Department of Zoology.
    Karlsson, Bengt
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology. Zoologisk ekologi.
    Habitat choice precedes host plant choice - niche separation in a species pair of a generalist and a specialist butterfly2008In: Oikos, Vol. 117, no 9, p. 1337-1344Article in journal (Refereed)
    Abstract [en]

    The sister species Leptidea reali and L. sinapis have partitioned their niches differently in different parts of their sympatric distribution. In Spain and France L. sinapis is a widespread generalist whereas L. reali is specialized on high altitude open areas. Interestingly, the reverse is true in Ireland and the Czech Republic where L. reali is widespread and L. sinapis specialized on meadows. In Sweden, L. reali is a habitat specialist confined to meadows, whereas L. sinapis is a habitat generalist also inhabiting forests. Ultimately, the geographic mosaic of niche separation is the result of local processes in each contact zone or a secondary effect of the host plant distribution, if L. sinapis and L. reali prefer different legume host plants. Hence, in Sweden L. sinapis might utilize the forest habitat either due to a wider habitat preference or due to a wider host plant preference than L. reali. Studies of wild butterflies showed that L. sinapis laid 26% of their eggs on forest-associated legumes compared to 6% in L. reali, although laboratory experiments showed that both species had virtually identical host plant preferences strongly preferring the meadow-associated legume Lathyrus pratensis. Furthermore, flight duration tests in a variety of temperatures demonstrated a between-species difference; L. sinapis females reached their flight optimum at a lower temperature than L. reali females. The lower L. sinapis flight temperature optimum is most probably a secondary effect due to habitat-specific selection, and therefore a consequence rather than the cause of the habitat partitioning. The finding that habitat choice precedes host plant choice suggests that the European geographic mosaic of niche separation, with L. sinapis and L. reali shifting habitat specialist/generalist roles, is not caused by rigid between-species differences in a related niche parameter, but instead is a result of local processes within each secondary contact zone.

  • 16.
    Friberg, Magne
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. Zoologisk ekologi.
    Vongvanich, Namphung
    Borg-Karlsson, Anna-Karin
    Kemp, Darrell
    Merilaita, Sami
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Female mate choice determines reproductive isolation between sympatric butterflies2008In: Behavioral Ecology and Sociobiology, Vol. 62, p. 873-886Article in journal (Refereed)
  • 17.
    Friberg, Magne
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. Evolutionär ekologi.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology. Evolutionär ekologi.
    Generation-dependent female choice: behavioral polyphenism in a bivoltine butterfly2007In: Behavioral Ecology, ISSN 1045-2249, Vol. 18, no 4, p. 758-763Article in journal (Refereed)
    Abstract [en]

    Climatic and biotic circumstances vary as seasons shift, and different cohorts of multivoltine species are likely subjected to different selection regimes. The bivoltine butterfly Leptidea reali (Re´al’s wood white; Lepidoptera: Pieridae) appears during May and June in central Sweden and has a partial second generation in late July. We manipulated both generations to appear simultaneously and performed laboratory mating experiments that showed the presence of a behavioral polyphenism in mating propensity, which is induced during the developmental stages. Females of the summer generation expressed higher mating propensities than spring generation females. Spring females showed an increase in mating propensity with increasing age, whereas summer females accepted most matings already when they were only 1 or 2 days old. It is likely that larval time constraints, a lower abundance of males and a lower risk of accepting a male of their univoltine sister species Leptidea sinapis (wood white), have relaxed selection on mate discrimination among summer generation females. A major challenge for future research is to further investigate the developmental pathways causing the polyphenism and the adaptive implications of cohort dependent behaviors.

  • 18.
    Friberg, Magne
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Host plant induced larval decision-making in a habitat/host plant generalist butterfly2010In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 91, p. 15-21Article in journal (Refereed)
    Abstract [en]

    Phenotypic plasticity can be a passive response to fluctuating environmental conditions or an active and presumably adaptive (evolved) response selected for in different environments. Here we ask if the larval decision to enter diapause when reared on a host plant associated with a colder habitat is an active or a passive response to host plant quality or suitability. We compare plasticity in larval propensity to enter diapause of the habitat generalist butterfly Leptidea sinapis and the meadow specialist Leptidea reali in a range of temperatures and long daylength on a forest plant, Lathyrus linifolius, and a meadow-associated plant, Lathyrus pratensis. The warmer meadow habitat promotes direct development whereas the colder forest habitat is conducive to diapause. Larvae of L. sinapis had a higher propensity to enter diapause when reared on the forest plant L. linifolius across all temperatures. Conversely, the propensity of L. reali to enter diapause was consistently lower and did not differ between host plants. Larval growth rates were similar between and within butterfly species and between host plants. Hence, we conclude that larval pathway decision-making in L. sinapis is an active response mediated by information from their host plants.

  • 19.
    Friberg, Magne
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Host plant preference and performance of the sibling species of butterflies Leptidea sinapis and Leptidea reali: a test of the trade-off hypothesis for food specialisation.2009In: Oecologia, ISSN 0029-8549, Vol. 159, no 1, p. 127-137Article in journal (Refereed)
    Abstract [en]

    A large proportion of phytophagous insect species are specialised on one or a few host plants, and female host plant preference is predicted to be tightly linked to high larval survival and performance on the preferred plant(s). Specialisation is likely favoured by selection under stable circumstances, since different host plant species are likely to differ in suitability-a pattern usually explained by the "trade-off hypothesis", which posits that increased performance on a given plant comes at a cost of decreased performance on other plants. Host plant specialisation is also ascribed an important role in host shift speciation, where different incipient species specialise on different host plants. Hence, it is important to determine the role of host plants when studying species divergence and niche partitioning between closely related species, such as the butterfly species pair Leptidea sinapis and Leptidea reali. In Sweden, Leptidea sinapis is a habitat generalist, appearing in both forests and meadows, whereas Leptidea reali is specialised on meadows. Here, we study the female preference and larval survival and performance in terms of growth rate, pupal weight and development time on the seven most-utilised host plants. Both species showed similar host plant rank orders, and larvae survived and performed equally well on most plants with the exceptions of two rarely utilised forest plants. We therefore conclude that differences in preference or performance on plants from the two habitats do not drive, or maintain, niche separation, and we argue that the results of this study do not support the trade-off hypothesis for host plant specialisation, since the host plant generalist Leptidea sinapis survived and performed as well on the most preferred meadow host plant Lathyrus pratensis as did Leptidea reali although the generalist species also includes other plants in its host range.

  • 20.
    Friberg, Magne
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology. Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology. Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Nya rön om skogs- och ängsvitvingar: Vem är vem i fjärilsvärlden?2009In: Flora och Fauna, Vol. 104, no 1, p. 12-17Article, review/survey (Other (popular science, discussion, etc.))
  • 21.
    Friberg, Magne
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Leimar, Olof
    Stockholm University, Faculty of Science, Department of Zoology.
    Heterospecific courtships, Allee-effects and niche separation between Leptidea sinapis and Leptidea realiManuscript (preprint) (Other (popular science, discussion, etc.))
    Abstract [en]

    Increasing attention is given to coevolutionary studies and to the role of ecology in local adaptation. The coevolutionary process can act in parallel throughout the distribution of species that interact in similar ecologies, whereas species interacting in varied ecological conditions might coevolve in different directions in different local populations. The butterflies Leptidea sinapis and L. reali have partitioned their niches differently in different parts of their sympatric distribution, with one species being a local habitat generalist in several different regions, and a local specialist in other areas where the sister species has adopted the habitat generalist role. Niche separation is likely independent of resource competition in this phytophagous system, and we study the potential for heterospecific sexual interference competition to redefine the suitability of a habitat and select for niche separation. We used the average female mating success in large outdoor cage experiments that varied both the absolute and relative density of the two species to estimate potential fitness costs of being in local minority. The mating success was unaffected by absolute density (conspecifics/m2) but strongly affected by the proportion of con- and heterospecifics in each cage. The proportion of mated females was ten times higher when a conspecific couple spent the day alone in the cage compared to when the single couple shared the cage with five heterospecific pairs. Being in the minority thus resulted in strong sexual interference from the locally more common competitor. We propose that these Allee effects select for habitat specialisation in the locally rare species as individuals leaving the core population likely suffer decreased fitness from spending time in heterospecific courtship. Hence, habitat suitability might depend less on local resource availability and more on the presence or absence of a local sexual competitor in this system.

  • 22.
    Larsdotter Mellström, Helena
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Friberg, Magne
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Borg-Karlson, Anna-Karin
    KTH Royal Institute of Technology, School of Chemical Science and Engineering, Department of Chemistry.
    Murtazina, Rushana
    KTH Royal Institute of Technology, School of Chemical Science and Engineering, Department of Chemistry.
    Palm, Mikael
    KTH Royal Institute of Technology, School of Chemical Science and Engineering, Department of Chemistry.
    Wiklund, Christer
    Stockholm University, Faculty of Science, Department of Zoology.
    Seasonal polyphenism in life history traits: Time costs of direct development in a butterfly2010In: Behavioral Ecology and Sociobiology, ISSN 0340-5443, E-ISSN 1432-0762, Vol. 64, p. 1377-1383Article in journal (Refereed)
    Abstract [en]

    Insects with two or more generations per year will generally experience different selection regimes depending on the season, and accordingly show seasonal polyphenisms. In butterflies, seasonal polyphenism has been shown with respect to morphology, life history characteristics and behaviour. In temperate bivoltine species, the directly developing generation is more time-constrained than the diapause generation and this may affect various life history traits, such as mating propensity (time from eclosion to mating). Here we test whether mating propensity differs between generations in Pieris napi, along with several physiological parameters, for males sex pheromone synthesis, and for females ovigeny index and fecundity.

    As predicted, individuals of the directly developing generation – who have shorter time for pupal development - are more immature at eclosion; males take longer to synthesize the male sex pheromone after eclosion and also take longer to mate than diapause generation males. Females show the same physiological pattern, the directly developing females lay fewer eggs than diapausing females during the first days of their life. Nevertheless, the directly developing females mate faster after eclosion than diapausing females, indicating substantial adult time stress in this generation and possibly an adaptive value of shortening the pre-reproductive period.

    Our study highlights how time-stress can be predictably different between generations, affecting both life history and behaviour. By analyzing several life history traits simultaneously we adopt a multi-trait approach to examining how adaptations and developmental constraints likely interplay to shape these seasonal polyphenisms.

  • 23. Svensson, Erik I
    et al.
    Eroukhmanoff, Fabrice
    Friberg, Magne
    Stockholm University, Faculty of Science, Department of Zoology. Evolutionär Ekologi.
    Effects of natural and sexual selection on adaptive population divergence and premating isolation in a damselfly.2006In: Evolution, ISSN 0014-3820, Vol. 60, no 6, p. 1242-53Article in journal (Refereed)
    Abstract [en]

    The relative strength of different types of directional selection has seldom been compared directly in natural populations. A recent meta-analysis of phenotypic selection studies in natural populations suggested that directional sexual selection may be stronger in magnitude than directional natural selection, although this pattern may have partly been confounded by the different time scales over which selection was estimated. Knowledge about the strength of different types of selection is of general interest for understanding how selective forces affect adaptive population divergence and how they may influence speciation. We studied divergent selection on morphology in parapatric, natural damselfly (Calopteryx splendens) populations. Sexual selection was stronger than natural selection measured on the same traits, irrespective of the time scale over which sexual selection was measured. Visualization of the fitness surfaces indicated that population divergence in overall morphology is more strongly influenced by divergent sexual selection rather than natural selection. Courtship success of experimental immigrant males was lower than that of resident males, indicating incipient sexual isolation between these populations. We conclude that current and strong sexual selection promotes adaptive population divergence in this species and that premating sexual isolation may have arisen as a correlated response to divergent sexual selection. Our results highlight the importance of sexual selection, rather than natural selection in the adaptive radiation of odonates, and supports previous suggestions that divergent sexual selection promotes speciation in this group.

  • 24. Svensson, Erik I
    et al.
    Friberg, Magne
    Stockholm University, Faculty of Science, Department of Zoology.
    Selective predation on wing morphology in sympatric damselflies.2007In: American Naturalist, ISSN 1537-5323, Vol. 170, no 1, p. 101-12Article in journal (Refereed)
    Abstract [en]

    Although predation is thought to affect species divergence, the effects of predator-mediated natural selection on species divergence and in nonadaptive radiations have seldom been studied. Wing melanization in Calopteryx damselflies has important functions in sexual selection and interspecific interactions and in species recognition. The genus Calopteryx and other damselfly genera have also been put forward as examples of radiations driven by sexual selection. We show that avian predation strongly affects natural selection on wing morphology and male wing melanization in two congeneric and sympatric species of this genus (Calopteryx splendens and Calopteryx virgo). Predation risk was almost three times higher for C. virgo, which has an exaggerated degree of wing melanization, than it was for the less exaggerated, sympatric congener C. splendens. Selective predation on the exaggerated species C. virgo favored a reduction and redistribution of the wing melanin patch. There was evidence for nonlinear selection involving wing patch size, wing patch darkness, and wing length and width in C. splendens but weaker nonlinear selection on the same trait combinations in C. virgo. Selective predation could interfere with species divergence by sexual selection and may thus indirectly affect male interspecific interactions, reproductive isolation, and species coexistence in this genus.

  • 25. Svensson, Erik I
    et al.
    Karlsson, Kristina
    Friberg, Magne
    Stockholm University, Faculty of Science, Department of Zoology. Evolutionär Ekologi.
    Eroukhmanoff, Fabrice
    Gender differences in species recognition and the evolution of asymmetric sexual isolation.2007In: Current Biology, ISSN 0960-9822Article in journal (Refereed)
    Abstract [en]

    Closely related sympatric species are expected to evolve strong species discrimination because of the reinforcement of mate preferences [1–4]. Fitness costs of heterospecific matings are thought to be higher in females than in males, and females are therefore expected to show stronger species discrimination than males [5, 6]. Here, we investigated gender and species differences in sexual isolation in a sympatric species pair of Calopteryx damselflies. The genus Calopteryx is one of the classic examples of reproductive character displacement in evolutionary biology, with exaggerated interspecific differences in the amount of dark wing coloration when species become sympatric [7–9]. Experimental manipulation of the extent of dark wing coloration revealed that sexual isolation results from both female and male mate discrimination and that wing melanization functions as a species recognition character. Female choice of conspecific males is entirely based on wing coloration, whereas males in one species also use other species recognition cues in addition to wing color. Stronger species discrimination ability in males is presumably an evolutionary response to an elevated male predation risk caused by conspicuous wing coloration [10]. Gender differences in species discrimination and fitness costs of male courtship can thus shed new light on the evolution of asymmetric sexual isolation and the reinforcement of mate preferences [2–4, 11].

  • 26.
    Wiklund, Christer
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. Ekologi.
    Friberg, Magne
    Stockholm University, Faculty of Science, Department of Zoology. Ekologi.
    Enemy-free space and habitat-specific host specialization in a butterfly.2008In: Oecologia, ISSN 0029-8549, Vol. 157, no 2, p. 287-94Article in journal (Refereed)
    Abstract [en]

    The majority of herbivorous insects have relatively specialized food habits. This suggests that specialization has some advantage(s) over generalization. Traditionally, feeding specialization has been thought to be linked to digestive or other food-related physiological advantages, but recent theory suggests that generalist natural enemies of herbivorous insects can also provide a major selective pressure for restricted host plant range. The European swallowtail butterfly Papilio machaon utilizes various plants in the Apiaceae family as hosts, but is an ecological specialist being monophagous on Angelica archangelica in southern Sweden. This perennial monocarp grows in three seaside habitat types: (1) on the barren rocky shore in the absence of any surrounding vegetation, (2) on the rocky shore with some surrounding vegetation, and (3) on species-rich meadows. The rocky shore habitat harbors few invertebrate generalist predators, whereas a number of invertebrate predators abound in the meadowland habitat. Here, we test the importance of enemy-free space for feeding specialization in Papilio machaon by assessing survival of larvae placed by hand on A. archangelica in each of the three habitat types, and by assessing the habitat-specificity of adult female egg-laying behavior by recording the distribution of eggs laid by free-flying adult females among the three habitat types. Larval survival was substantially higher in the rocky shore habitat than in the meadowland and significantly higher on host plants without surrounding vegetation on the rocky shore. Eggs laid by free-flying females were found in all three habitat types, but were significantly more frequent in the rocky shore habitat, suggesting that females prefer to lay eggs in the habitat type where offspring survival is highest. These results show that larval survivorship on the same host plant species can be strongly habitat-specific, and suggest that enemy-free space is an underlying factor that drives feeding specialization in Papilio machaon.

  • 27.
    Wiklund, Christer
    et al.
    Stockholm University, Faculty of Science, Department of Zoology.
    Friberg, Magne
    Stockholm University.
    Seasonal development and variation in abundance among four annual flight periods in a butterfly: a 20-year study of the speckled wood (Pararge aegeria)2011In: Biological Journal of the Linnean Society, ISSN 0024-4066, E-ISSN 1095-8312, Vol. 102, no 3, p. 635-649Article in journal (Refereed)
    Abstract [en]

    Insects typically spend the winter in a species-specific diapause stage. The speckled wood butterfly, Pararge aegeria, is unique in having two alternative diapause stages, hibernating as larvae or pupae. In southern Sweden this creates a seasonal flight pattern with four annual adult flight periods: the first in May (pupal diapause), the second in June (larval diapause), and the third and fourth directly developing offspring generations in July and August, respectively. We address the raison d'être of the two diapause pathways by (1) outdoor rearing of cohorts, and (2) performing transect censuses throughout the season for 20 years. We contend that an early start of next season provides a benefit accruing to pupal diapause; conversely, a large proportion of the offspring from adults of the fourth flight peak are unable to reach the pupal stage before winter, providing a benefit accruing to larval winter diapause. The results obtained show that the two hibernation pathways are unlikely to be genetically distinct because of a strong overlap between the two offspring generations, and because sibling offspring from the third and fourth flight periods are likely to choose either of the two hibernation pathways, thereby resulting in a genetic mixing of the pathways

  • 28.
    Wiklund, Christer
    et al.
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    Friberg, Magne
    Stockholm University, Faculty of Science, Department of Zoology, Animal Ecology.
    The evolutionary ecology of generalization: among-year variation in host plant use and offspring survival in a butterfly2009In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 90, no 12, p. 3406-3417Article in journal (Refereed)
    Abstract [en]

    The majority of phytophagous insects are relatively specialized in their food habits, and specialization in resource use is expected to be favored by selection in most scenarios. Ecological generalization is less common and less well understood, but it should be selected for by (1) rarity of resources, (2) resource inconstancy, or (3) unreliability of resource quality. Here, we test these predictions by studying egg distribution and offspring survival in the orange tip butterfly, Anthocharis cardamines, on different host plants in Sweden over a five-year period. A total of 3800 eggs were laid on 16 of the 18 crucifers available at the field site during the five years. Three main factors explained host plant generalization: (1) a rarity of food resources in which the female encounter rate of individual crucifer plants was low and within-year phenological succession of flowering periods of the different crucifers meant that individual species were suitable for oviposition only within a short time window, which translates to a low effective abundance of individual crucifer species as experienced by females searching for host plants, making specialization on a single crucifer species unprofitable; (2) variation in food resources in which among-year variation in availability of any one host plant species was high; and (3) larval survivorship varied unpredictably among years on all host plants, thereby necessitating a bet-hedging strategy and use of several different host plants. Unpredictable larval survival was caused by variation in plant stand habitat characteristics, which meant that drowning and death from starvation affected different crucifers differently, and by parasitism, which varied by host plant and year. Hence, our findings are in agreement with the theoretical explanation of ecological generalization above, helping to explain why A. cardamines is a generalist throughout its range with respect to genera within the Cruciferae.

  • 29.
    Wiklund, Christer
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. Ekologiska avdelningen.
    Vallin, Adrian
    Stockholm University, Faculty of Science, Department of Zoology. Etologiska avdelningen.
    Friberg, Magne
    Stockholm University, Faculty of Science, Department of Zoology. Ekologiska avdelningen.
    Jakobsson, Sven
    Stockholm University, Faculty of Science, Department of Zoology. Etologiska avdelningen.
    Rodent predation on hibernating peacock and small tortoiseshell butterflies2007In: Behavioral ecology and sociobiologyArticle in journal (Refereed)
  • 30. Wiklund, Christer
    et al.
    Vallin, Adrian
    Stockholm University, Faculty of Science, Department of Zoology.
    Friberg, Magne
    Jakobsson, Sven
    Winter survival of hibernating butterflies – timing and targeting of rodent predationManuscript (Other (popular science, discussion, etc.))
1 - 30 of 30
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