Latitudinal clines in alternative life histories in a geometrid moth

The relative roles of genetic differentiation and developmental plasticity in generating latitudinal gradients in life histories remain insufficiently understood. In particular, this applies to determination of voltinism (annual number of generations) in short‐lived ectotherms, and the associated trait values. We studied different components of variation in development of Chiasmia clathrata (Lepidoptera: Geometridae) larvae that originated from populations expressing univoltine, partially bivoltine or bivoltine phenology along a latitudinal gradient of season length. Indicative of population‐level genetic differentiation, larval period became longer while growth rate decreased with increasing season length within a particular phenology, but saw‐tooth clines emerged across the phenologies. Indicative of phenotypic plasticity, individuals that developed directly into reproductive adults had shorter development times and higher growth rates than those entering diapause. The most marked differences between the alternative developmental pathways were found in the bivoltine region suggesting that the adaptive correlates of the direct development evolve if exposed to selection. Pupal mass followed a complex cline without clear reference to the shift in voltinism or developmental pathway probably due to varying interplay between the responses in development time and growth rate. The results highlight the multidimensionality of evolutionary trajectories of life‐history traits, which either facilitate or constrain the evolution of integrated traits in alternative phenotypes.     

Seasonal plasticity in life history traits: growth and development in Polygonia c-album (Lepidoptera: Nymphalidae)

The potentially multivoltine comma butterfly, Polygonia c-album L., hibernates in the adult stage. The adult seasonal morph is demonstrated to be a good indicator of whether an individual has entered reproductive diapause or is developing directly to sexual maturation. This fact, and the assumption that a short development time is not equally important to all categories of individuals, was used to test predictions on variation in life-history traits among categories (morphs and sexes) and environments (temperature and photoperiod) at the level of individuals and to some extent families and populations (the univoltine Stockholm population and the partially bivoltine Oxford population). Individuals developing to adults in a short time were expected to be smaller and lighter as a result of a basic trade-off between the two traits. Development times varied in accordance with predictions, but in most cases this was due to plastic growth and development in both the larval and pupal stages rather than through variation in size or weight, i.e. size was a highly canalized trait. This suggests a relationship between plasticity and canalization and a strong potential for plasticity to shield life-history traits from selection. Individuals regulated development times also within developmental pathways, in response to photoperiods indicating the progression of the season. These and other results suggest that development times are not normally minimized in temperate butterflies unless this is enforced by direct development and protandry. There is thus scope for a high degree of adaptive plasticity in growth- and developmental rates which may devalue the basic trade-offs assumed by life-history theory and account for inconsistencies with its predictions.     

Evolution of adaptive phenotypic traits without positive Darwinian selection

Recent evidence suggests the frequent occurrence of a simple non-Darwinian (but non-Lamarckian) model for the evolution of adaptive phenotypic traits, here entitled the plasticity-relaxation-mutation (PRM) mechanism. This mechanism involves ancestral phenotypic plasticity followed by specialization in one alternative environment and thus the permanent expression of one alternative phenotype. Once this specialization occurs, purifying selection on the molecular basis of other phenotypes is relaxed. Finally, mutations that permanently eliminate the pathways leading to alternative phenotypes can be fixed by genetic drift. Although the generality of the PRM mechanism is at present unknown, I discuss evidence for its widespread occurrence, including the prevalence of exaptations in evolution, evidence that phenotypic plasticity has preceded adaptation in a number of taxa and evidence that adaptive traits have resulted from loss of alternative developmental pathways. The PRM mechanism can easily explain cases of explosive adaptive radiation, as well as recently reported cases of apparent adaptive evolution over ecological time.     

Thermal plasticity of growth and development varies adaptively among alternative developmental pathways

Polyphenism, the expression of discrete alternative phenotypes, is often a consequence of a developmental switch. Physiological changes induced by a developmental switch potentially affect reaction norms, but the evolution and existence of alternative reaction norms remains poorly understood. Here, we demonstrate that, in the butterfly Pieris napi (Lepidoptera: Pieridae), thermal reaction norms of several life history traits vary adaptively among switch‐induced alternative developmental pathways of diapause and direct development. The switch was affected both by photoperiod and temperature, ambient temperature during late development having the potential to override earlier photoperiodic cues. Directly developing larvae had higher development and growth rates than diapausing ones across the studied thermal gradient. Reaction norm shapes also differed between the alternative developmental pathways, indicating pathway‐specific selection on thermal sensitivity. Relative mass increments decreased linearly with increasing temperature and were higher under direct development than diapause. Contrary to predictions, population phenology did not explain trait variation or thermal sensitivity, but our experimental design probably lacks power for finding subtle phenology effects. We demonstrate adaptive differentiation in thermal reaction norms among alternative phenotypes, and suggest that the consequences of an environmentally dependent developmental switch primarily drive the evolution of alternative thermal reaction norms in P. napi.     

Genetic and phenotypic variation in juvenile development in relation to temperature and developmental pathway in a geometrid moth

Life histories show genetic population-level variation due to spatial variation in selection pressures. Phenotypic plasticity in life histories is also common, facilitating fine-tuning of the phenotype in relation to the prevailing selection regime. In multivoltine (≥ 2 generations per year) insects, individuals following alternative developmental pathways (diapause/direct development) experience different selection regimes. We studied the genetic and phenotypic components of juvenile development in Cabera exanthemata (Lepidoptera: Geometridae) in a factorial split-brood experiment. F(2) offspring of individuals originating from populations in northern and central Finland were divided among manipulations defined by temperature (14°C/20°C) and day length (24 h/15 h). Short day length invariably induced diapause, whereas continuous light almost invariably induced direct development in both regions, although northern populations are strictly univoltine in the wild. Individuals from northern Finland had higher growth rates, shorter development times and higher pupal masses than individuals from central Finland across the conditions, indicating genetic differences between regions. Individuals that developed directly into adults tended to have higher growth rates, shorter development times and higher pupal masses than those entering diapause, indicating phenotypic plasticity. Temperature-induced plasticity was substantial; growth rate was much higher, development time much shorter and pupal mass higher at 20°C than at 14°C. The degree of plasticity in relation to developmental pathway was pronounced at 20°C in growth rate and development time and at 14°C in pupal mass, emphasizing multidimensionality of reaction norms. The observed genetic variation and developmental plasticity seem adaptive in relation to time-stress due to seasonality.     

Temperature- and density-dependence of diapause induction and its life history correlates in the geometrid moth Chiasmia clathrata (Lepidoptera: Geometridae)

The relative roles of genetics and developmental plasticity in creating phenotypes adapted to prevailing conditions are insufficiently understood. In potentially multivoltine temperate insects, individuals that do not enter diapause but develop directly into reproductive adults within the same season are severely time-constrained. Direct development is, however, under selection only if expressed in the wild. Thus, adaptive correlates of the direct development are expected to evolve and persist only in multivoltine populations. We studied the genetic and phenotypic components of variation in juvenile development in the geometrid moth Chiasmia clathrata from univoltine and bivoltine regions. Larvae were reared at two temperatures (14/20 °C) and densities (low/high) in a factorial split-brood experiment. High temperature and low density promoted direct development, the former condition being associated with a short development time, high growth rate and large body size. Genotypes of bivoltine origin had a higher propensity for direct development and seemingly expressed an exaggerated plastic response to increasing temperature compared to the ones from univoltine populations. Alternative life history phenotypes associated with the induced developmental pathway emerged only in the bivoltine region, direct development resulting in a short larval period, high growth rate and small size at 20 °C there. The degree of differentiation between the developmental pathways was insensitive to larval density; high density only decreased both development time and body size to a certain degree. We conclude that the differences between the pathways are not due to the induction of a particular pathway itself, but geographically varying selection pressures shape the correlation structure among life history traits and their pathway-specific expression.     

Covariation of larval gene expression and adult body size in natural populations of Drosophila melanogaster

Understanding adaptive phenotypic variation is one of the most fundamental problems in evolutionary biology. Genes involved in adaptation are most likely those that affect traits most intimately connected to fitness: life-history traits. The genetics of quantitative trait variation (including life histories) is still poorly understood, but several studies suggest that (1) quantitative variation might be the result of variation in gene expression, rather than protein evolution, and (2) natural variation in gene expression underlies adaptation. The next step in studying the genetics of adaptive phenotypic variation is therefore an analysis of naturally occuring covariation of global gene expression and a life-history trait. Here, we report a microarray study addressing the covariation in larval gene expression and adult body weight, a life-history trait involved in adaptation. Natural populations of Drosophila melanogaster show adaptive geographic variation in adult body size, with larger animals at higher latitudes. Conditions during larval development also affect adult size with larger flies emerging at lower temperatures. We found statistically significant differences in normalized larval gene expression between geographic populations at one temperature (genetic variation) and within geographic populations between temperatures (developmental plasticity). Moreover, larval gene expression correlated highly with adult weight, explaining 81% of its natural variation. Of the genes that show a correlation of gene expression with adult weight, most are involved in cell growth or cell maintenance or are associated with growth pathways.     

Does phenotypic plasticity initiate developmental bias?

The generation of variation is paramount for the action of natural selection. Although biologists are now moving beyond the idea that random mutation provides the sole source of variation for adaptive evolution, we still assume that variation occurs randomly. In this review, we discuss an alternative view for how phenotypic plasticity, which has become well accepted as a source of phenotypic variation within evolutionary biology, can generate nonrandom variation. Although phenotypic plasticity is often defined as a property of a genotype, we argue that it needs to be considered more explicitly as a property of developmental systems involving more than the genotype. We provide examples of where plasticity could be initiating developmental bias, either through direct active responses to similar stimuli across populations or as the result of programmed variation within developmental systems. Such biased variation can echo past adaptations that reflect the evolutionary history of a lineage but can also serve to initiate evolution when environments change. Such adaptive programs can remain latent for millions of years and allow development to harbor an array of complex adaptations that can initiate new bouts of evolution. Specifically, we address how ideas such as the flexible stem hypothesis and cryptic genetic variation overlap, how modularity among traits can direct the outcomes of plasticity, and how the structure of developmental signaling pathways is limited to a few outcomes. We highlight key questions throughout and conclude by providing suggestions for future research that can address how plasticity initiates and harbors developmental bias.     

LABORATORY EVOLUTION OF LIFE-HISTORY TRAITS IN THE BEAN WEEVIL (ACANTHOSCELIDES OBTECTUS): THE EFFECTS OF SELECTION ON DEVELOPMENTAL TIME IN POPULATIONS WITH DIFFERENT PREVIOUS HISTORY

In this study we examined the direct and correlated responses for fast and slow preadult development time in three laboratory populations of the bean weevil (Acanthoscelides obtectus). The first population (“base,” B) has experienced laboratory conditions for more than 10 years; the second (“young,” Y) and the third (“old,” O) populations were selected for early and late reproduction, respectively, before the onset of the present experiments. All three populations are successfully selected for both fast and slow preadult development. The realized heritabilities are very similar in all populations, suggesting a similar level of the additive genetic variance for preadult development. We studied the correlated responses on the following life-history traits: egg-to-adult viability, wet body weight, early fecundity, late fecundity, total realized female fecundity, and adult longevity. All life-history traits examined here, except for the egg-to-adult viability, are affected by selection for preadult development in at least in one of the studied populations. In all three populations, beetles selected for slow preadult development are heavier and live longer than those from the fast-selected lines. The findings with respect to adult longevity are unexpected, because the control Y and O populations, selected for short- and long-lived beetles, respectively, do not show significant differences in preadult development. Thus, our results indicate that some kind of asymmetrical correlated responses occur for preadult development and adult longevity each time that direct selection has been imposed on one or the other of these two traits. In contrast to studies with Drosophila, it appears that for insect species that are aphagous as adults, selection for preadult development entails selection for alleles that also change the adult longevity, but that age-specific selection (applied in the Y and O populations) mostly affects the alleles that have no significant influence on the preadult development. Implications of these findings on the developmental and evolutionary theories of aging are also discussed.     

Reproductive diapause and life-history clines in North American populations of Drosophila melanogaster

Latitudinal clines are widespread in Drosophila melanogaster, and many have been interpreted as adaptive responses to climatic variation. However, the selective mechanisms generating many such patterns remain unresolved, and there is relatively little information regarding how basic life-history components such as fecundity, life span and mortality rates vary across environmental gradients. Here, it is shown that four life-history traits vary predictably with geographic origin of populations sampled along the latitudinal gradient in the eastern United States. Although such patterns are indicative of selection, they cannot distinguish between the direct action of selection on the traits in question or indirect selection by means of underlying genetic correlations. When independent suites of traits covary with geography, it is therefore critical to separate the widespread effects of population source from variation specifically for the traits under investigation. One trait that is associated with variation in life histories and also varies with latitude is the propensity to express reproductive diapause; diapause expression has been hypothesized as a mechanism by which D. melanogaster adults overwinter, and as such may be subject to strong selection in temperate habitats. In this study, recently derived isofemale lines were used to assess the relative contributions of population source and diapause genotype in generating the observed variance for life histories. It is shown that although life span, fecundity and mortality rates varied predictably with geography, diapause genotype explained the majority of the variance for these traits in the sampled populations. Both heat and cold shock resistance were also observed to vary predictably with latitude for the sampled populations. Cold shock tolerance varied between diapause genotypes and the magnitude of this difference varied with geography, whereas heat shock tolerance was affected solely by geographic origin of the populations. These data suggest that a subset of life-history parameters is significantly influenced by the genetic variance for diapause expression in natural populations, and that the observed variance for longevity and fecundity profiles may reflect indirect action of selection on diapause and other correlated traits.     

CONTRASTING PATTERNS OF HERITABLE GEOGRAPHIC VARIATION IN SHELL MORPHOLOGY AND GROWTH POTENTIAL IN THE MARINE GASTROPOD BEMBICIUM VITTATUM: EVIDENCE FROM FIELD EXPERIMENTS

Similar phenotypes do not always imply similar genotypes. In species distributed over a broad latitudinal range, geographical variation in morphological and life-history traits may reflect very different relations between genotypic and environmental effects on these traits. Patterns of selection among latitudinally separated sites may minimize phenotypic differences in life-history traits but promote phenotypic differences in form. Thus, for example, latitudinal variation in temperature often leads to genetically based metabolic differences that minimize differences in growth rate among populations at different latitudes (countergradient variation). However, variation in habitat experienced by the same populations may promote genetically based differences in shell form (cogradient variation). Few attempts have been made to assess simultaneously such mosaic effects of natural selection on the genetic basis of variation in both morphological and life-history traits among geographically separated populations. I quantified the extent to which widely separated populations of the rocky shore marine gastropod Bembicium vittatum exhibited genetic differences in shell shape, shell pattern, and growth rate. Bembicium vittatum occurs naturally at only three widely separated locations on the Western Australian coast. Individuals were transplanted from all three locations to a latitudinally intermediate site, where they were released in different pairwise combinations and allowed to reproduce. F₁ offspring from crosses between same- or different-source parents were identified using allozyme markers. When grown in a common environment, offspring from same-source parents exhibited similar differences in shell shape and pattern, but dramatic differences in growth rates, compared to native populations. Genetic variation therefore exists for all three traits. Growth rates in the common environment were positively correlated with latitude of the source population, confirming the existence of countergradient variation for growth associated with metabolic compensation. In addition, for both shell shape and growth rate, hybrids exhibited phenotypes roughly midway between the same-source parents, suggesting that genetic differences have a large additive component. In contrast, when one parent had pigmented spots, the offspring also had spots, suggesting a strong dominance component to the genetic basis of shell pattern. Genetic differences therefore yield different morphological phenotypes but similar life-history phenotypes, among latitudinally distant populations, and confirm a pattern of mosaic evolution in B. vittatum.     

Seasonal plasticity in growth and development of the speckled wood butterfly, Pararge aegeria (Satyrinae)

Regulation of growth and development by photoperiod was studied in a population of the speckled wood butterfly, Purarge aegeria L. (Lepidoptera: Satyrinae), from southern Sweden. Individuals were reared in a range of photoperiodic regimes (9L. to 22L) and temperatures (13°C to 21° C). Plasticity was found for important life-history traits- generation time, growth rate and final weight and seasonal regulation of development in response to photoperiod was found to occur at two levels. Purarge aegeria hibernates as a third instar larva or in the pupal stage, cantering one of four major developmental pathways in response to photoperiod: (1) direct development in both the larval and pupal stages, (2) pupal winter diapause with or (3) without a preceding larval summer diapause, or (4) larval winter diapause. In addition to this high-level regulation of individual development, larval growth rate and pupal development rate also appear to be finally regulated by photoperiod within each major pathway. As photoperiods decreased from 22 h to 17 h at 17° C, growth rate among directly developing larvae increased progressively, as was the case for larva? developing according to a univoltine life cycle from 17 h to 14 h. At two photoperiods, 13 h and 16 h (corresponding to shifts between major pathways), both larval and pupal development were extremely variable with the fastest individuals developing directly and the slowest developing with a diapause. This indicates a gradual nature of diapause itself, suggesting that the two level may not he fundamentally different.     

High temperatures reveal cryptic genetic variation in a polymorphic female sperm storage organ

Variation in female reproductive morphology may play a decisive role in reproductive isolation by affecting the relative fertilization success of alternative male phenotypes. Yet, knowledge of how environmental variation may influence the development of the female reproductive tract and thus alter the arena of postcopulatory sexual selection is limited. Yellow dung fly females possess either three or four sperm storage compartments, a polymorphism with documented influence on sperm precedence. We performed a quantitative genetics study including 12 populations reared at three developmental temperatures complemented by extensive field data to show that warm developmental temperatures increase the frequency of females with four compartments, revealing striking hidden genetic variation for the polymorphism. Systematic genetic differentiation in growth rate and spermathecal number along latitude, and phenotypic covariance between the traits across temperature treatments suggest that the genetic architecture underlying the polymorphism is shaped by selection on metabolic rate. Our findings illustrate how temperature can modulate the preconditions for sexual selection by differentially exposing novel variation in reproductive morphology. This implies that environmental change may substantially alter the dynamics of sexual selection. We further discuss how temperature-dependent developmental plasticity may have contributed to observed rapid evolutionary transitions in spermathecal morphology.     

Adaptive inter-population differences in blue tit life-history traits on Corsica

Few studies of natural populations have investigated how phenotypic variation across populations relates to key factors in the environment and landscape structure. In the blue tits of southern France, inter-population differences in reproductive life-history traits (e.g. laying date and clutch size) are small, whatever the timing of maximum caterpillar availability, a key factor for offspring survival in tits. These small differences are attributed to gene flow between local populations occupying different habitat types. In contrast, in blue tits on the island of Corsica, we noted large differences in reproductive life-history traits between two populations, where each population is synchronized with the peak-date of caterpillar abundance. These occur over a short geographical distance (25km). Considering our study within a framework of long-term population studies in tits, our results support the hypothesis that different blue tit populations on Corsica show adaptive differences in life-history traits, and suggest that landscape structure at a small spatial scale can have profound effects on adaptive between-population differentiation in life-history traits that are closely linked with fitness.     

Keeping up with a warming world; assessing the rate of adaptation to climate change

The pivotal question in the debate on the ecological effects of climate change is whether species will be able to adapt fast enough to keep up with their changing environment. If we establish the maximal rate of adaptation, this will set an upper limit to the rate at which temperatures can increase without loss of biodiversity.The rate of adaptation will primarily be set by the rate of microevolution since (i) phenotypic plasticity alone is not sufficient as reaction norms will no longer be adaptive and hence microevolution on the reaction norm is needed, (ii) learning will be favourable to the individual but cannot be passed on to the next generations, (iii) maternal effects may play a role but, as with other forms of phenotypic plasticity, the response of offspring to the maternal cues will no longer be adaptive in a changing environment, and (iv) adaptation via immigration of individuals with genotypes adapted to warmer environments also involves microevolution as these genotypes are better adapted in terms of temperature, but not in terms of, for instance, photoperiod.Long-term studies on wild populations with individually known animals play an essential role in detecting and understanding the temporal trends in life-history traits, and to estimate the heritability of, and selection pressures on, life-history traits. However, additional measurements on other trophic levels and on the mechanisms underlying phenotypic plasticity are needed to predict the rate of microevolution, especially under changing conditions.Using this knowledge on heritability of, and selection on, life-history traits, in combination with climate scenarios, we will be able to predict the rate of adaptation for different climate scenarios. The final step is to use ecoevolutionary dynamical models to make the link to population viability and from there to biodiversity loss for those scenarios where the rate of adaptation is insufficient.     

Correlated evolution of life-history with size at maturity in Daphnia pulicaria: patterns within and between populations

Explaining the repeated evolution of similar sets of traits under similar environmental conditions is an important issue in evolutionary biology. The extreme alternative classes of explanations for correlated suites of traits are optimal adaptation and genetic constraint resulting from pleiotropy. Adaptive explanations presume that individual traits are free to evolve to their local optima and that convergent evolution represents particularly adaptive combinations of traits. Alternatively, if pleiotropy is strong and difficult to break, strong selection on one or a few particularly important characters would be expected to result in consistent correlated evolution of associated traits. If pleiotropy is common, we predict that the pattern of divergence among populations will consistently reflect the within-population genetic architecture. To test the idea that the multivariate life-history phenotype is largely a byproduct of strong selection on body size, we imposed divergent artificial selection on size at maturity upon two populations of the cladoceran Daphnia pulicaria, chosen on the basis of their extreme divergence in body size. Overall, the trajectory of divergence between the two natural populations did not differ from that predicted by the genetic architecture within each population. However, the pattern of correlated responses suggested the presence of strong pleiotropic constraints only for adult body size and not for other life-history traits. One trait, offspring size, appears to have evolved in a way different from that expected from the within-population genetic architecture and may be under stabilizing selection.     

Within-Population Developmental and Morphological Plasticity is Mirrored in Between-Population Differences: Linking Plasticity and Diversity

It has been suggested that phenotypic plasticity can facilitate evolutionary diversification of organisms. If life-history and morphological diversification across a lineage is mirrored in diversification in the same traits due to phenotypic plasticity within a lineage it fulfils one of the expectations that are needed to support this diversification hypothesis. We carried out a laboratory study to examine development rate and morphology between and within populations of the parsley frog, Pelodytes punctatus. We found that frogs reared in the laboratory had a longer development time, relatively longer hind legs and relatively narrower heads under constant water level compared to those under decreasing water level simulating pool drying. This adaptive phenotypic plasticity response to pool drying was mirrored across populations because frogs from permanent waters had longer development times, relatively longer hind legs and relatively narrower heads compared to frogs from temporary waters. Hence the developmental and morphological plasticity observed within populations was also observed between populations as constitutive expressed traits. We suggest that the morphology pattern observed was driven by a common developmental process (time to metamorphosis), indicating that plasticity may contribute to evolutionary change, ultimately resulting in genetic accommodation of the morphological traits.     

EVALUATING A HYPOTHESIS ABOUT HETEROCHRONY: LARVAL LIFE-HISTORY TRAITS AND JUVENILE HIND-LIMB MORPHOLOGY IN HYLA CRUCIFER

This paper reports the results of an investigation into whether selection on genetically based differences in the timing or rate of development (heterochrony) can give rise to nonadaptive morphological differences among individual frogs. We used a quantitative-genetics approach to examine the relationships among the life-history characters time to metamorphosis and larval-growth rate and a functionally significant morphological features, relative hind-limb length, in the spring peeper, Hyla crucifer. Time to metamorphosis and growth rate had low heritabilities in our population. Morphological traits had moderate heritabilities. There were positive genetic correlations between the life-history traits and the components of relative hind-limb length but no significant correlations with the shape variable itself. We used field observations of pond-drying time and experimental results of selection on growth rate to simulate the correlated responses of hind-limb shape to four reasonable selection regimes on the life-history traits. We found little evidence to suggest that relative hind-limb length would display much of a correlated response to such selection. The differences in relative hind-limb length seen among closely related species or among populations of a single species that appear to be unrelated to performance differences are not obviously explicable as neutral correlated responses to selection on larval traits.     

Interpopulation variation in life-history traits of Poeciliopsis prolifica: implications for the study of placental evolution

Placental reproduction is widespread across vertebrate taxa, but little is known about its life-history correlates and putative adaptive value. We studied variation in life-history traits in two populations of the placental poeciliid fish Poeciliopsis prolifica to determine whether differences in post-fertilization maternal provisioning to embryos have a genetic basis and how food availability affects reproduction. Life histories were characterized for wild-caught females and for second-generation lab-born females raised under two levels of food availability. We found that the two populations did not differ significantly in the wild for any life-history traits except for the lipid dry weight in females and in embryos at an advanced stage of development. When environmental effects were experimentally controlled, however, populations exhibited significant differences in several traits, including the degree of maternal provisioning to embryos. Food availability significantly affected female size at first parturition, brood size and offspring dry weight at birth. Altogether, these results demonstrate that population differences in maternal provisioning and other life-history traits have a genetic basis and show a plastic response to food availability. We infer that phenotypic plasticity may mask population differences in the field. In addition, when comparing life-history patterns in these two populations with known patterns in placental and non-placental poeciliids, our results support the hypotheses that placentation is an adaptive reproductive strategy under high-resource conditions but that it may represent a cost under low-food conditions. Finally, our results highlight that age at maturity and reproductive allotment may be key life-history traits accompanying placental evolution.     

Within- and between-generation effects of temperature on life-history traits in a butterfly

Non-genetic parental effects may largely affect offspring phenotype, and such plasticity is potentially adaptive. Despite its potential importance, little is known about cross-generational effects of temperature, at least partly because parental effects were frequently considered a troublesome nuisance, rather than a target of experimental studies. We here investigate effects of parental, developmental and acclimation temperature on life-history traits in the butterfly Bicyclus anynana. Higher developmental temperatures reduced development times and egg size, increased egg number, but did not affect pupal mass. Between-generation temperature effects on larval time, pupal time, larval growth rate and egg size were qualitatively very similar to effects of developmental temperature, and additionally affected pupal mass but not egg number. Parental effects are important mediators of phenotypic plasticity in B. anynana, and partly yielded antagonistic effects on different components of fitness, which may constrain the evolution of cross-generational adaptive plasticity.