A Review for Life-history Traits Variation in Frogs Especially for Anurans in China

Environmental variation can promote differentiation in life-history traits in species of anurans. Increased environmental stress usually results in larger age at sexual maturity, older mean age, longer longevity, slower growth, larger body size, and a shift in reproductive allocation from offspring quantity to quality, and a stronger trade-off between offspring size and number. However, previous studies have suggested that there are inconsistent geographical variations in life-history traits among anuran species in China. Hence, we here review the intraspecific patterns and differences in life-history traits(i.e., egg size, clutch size, testes size, sperm length, age at sexual maturity, longevity, body size and sexual size dimorphism) among different populations within species along geographical gradients for anurans in China in recent years. We also provide future directions for studying difference in sperm performance between longer and shorter sperm within a species through transplant experiments and the relationships between metabolic rate and brain size and life-history.     

Comparing latitudinal and upstream–downstream gradients: life history traits of invasive mosquitofish

Aim Variation of life history traits along spatial gradients is poorly understood in invasive species and particularly in freshwater fish. We aimed to examine life history variation in a highly invasive fish (Gambusia holbrooki) along latitudinal and upstream–downstream river gradients and to assess the effects of age on this variation. We hypothesized similar responses in populations inhabiting environments more favourable to this species (lower latitudes and lower reaches of rivers). Location European rivers from southern Spain to southern France. Methods We sampled mosquitofish from the lowest reaches of ten river basins along 6° of latitude in the Mediterranean region and seven sites along the upstream–downstream gradient in three of the rivers. We examined abundance, population structure, size‐at‐age and other life history traits along these gradients. Results As hypothesized, lower reaches and lower latitudes both resulted in higher reproductive effort and lower body condition of mosquitofish. However, these patterns explained low per cent variation, were nonlinear and strongly depended on fish age. Independently of fish size, age groups differed in reproductive effort, in the gonadal weight–size relationship and its variation along spatial gradients. Mean size‐at‐age (or overall body size) did not vary with latitude (so the intra‐specific version of Bergmann’s rule or its converse does not apply) and in contrast increased upstream in rivers. Main conclusions Our findings suggest that for life history traits of freshwater organisms, river longitudinal variation plays a role as important as climate, with often differential effects. Our results also illustrate the poor knowledge of spatial variation of many life history traits, which precludes the understanding and prediction of biological invasions in a rapidly changing world.     

Climate and mammalian life histories

Mammals display considerable geographical variation in life history traits. To understand how climatic factors might influence this variation, we analysed the relationship between life history traits – adult body size, litter size, number of litters per year, gestation length, neonate body mass, weaning age and age at sexual maturity – and several environmental variables quantifying the seasonality and predictability of temperature and precipitation across the distribution range of five terrestrial mammal groups. Environmental factors correlated strongly with each other; therefore, we used principal components analysis to obtain orthogonal climatic predictors that could be used in multivariate models. We found that in bats, primates and even‐toed ungulates adult body size tends to be larger in species inhabiting cold, dry, seasonal environments, whereas in carnivores and rodents a smaller body size is characteristic of warm, dry environments, suggesting that low food availability might limit adult size. Species inhabiting cold, dry, seasonal habitats have fewer, larger litters and shorter gestation periods; however, annual fecundity in these species is not higher, implying that the large litter size of mammals living at high latitudes is probably a consequence of time constraints imposed by strong seasonality. On the other hand, the number of litters per year and annual fecundity were greater in species inhabiting environments with higher seasonality in precipitation. Lastly, we found little evidence for specific effects of environmental variability. Our results highlight the complex effects of environmental factors in the evolution of life history traits in mammals. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 719–736.     

An invasive species imposes selection on life‐history traits of a native frog

As well as their direct ecological impacts on native taxa, invasive species can impose selection on phenotypic attributes (morphology, physiology, behaviour, etc.) of the native fauna. In anurans, body size at metamorphosis is a critical life‐history trait: for most challenges faced by post‐metamorphic anurans, larger size at metamorphosis probably enhances survival. However, our studies on Australian frogs (Limnodynastes convexiusculus) show that this pattern can be reversed by the arrival of an invasive species. When metamorph frogs first encounter invasive cane toads (Bufo marinus), they try to eat the toxic invader and, if they are able to do so, are likely to die from poisoning. Because frogs are gape‐limited predators, small metamorphs cannot ingest a toad and thus survive long enough to disperse away from the natal pond (and thus from potentially deadly toads). These data show that larger size at metamorphosis can reduce rather than increase anuran survival rates, because larger metamorphs are more easily able to ingest (and thus be poisoned by) metamorph cane toads. Our results suggest that patterns of selection on life‐history traits of native taxa (such as size and age at metamorphosis, seasonal timing of breeding and duration of pondside aggregation prior to dispersal) can be modified by the arrival of an invasive species. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 329–336.     

Comparative demography of commercially important parrotfish species from Micronesia

Fishery‐independent sampling was used to determine growth patterns, life span, mortality rates and timing of maturation and sex change in 12 common parrotfishes (Labridae: tribe Scarinae) from five genera (Calotomus, Cetoscarus, Chlorurus, Hipposcarus and Scarus) in Micronesia. Interspecific variation in life‐history traits was explored using multivariate analysis. All species displayed strong sex‐specific patterns of length‐at‐age among which males reached larger asymptotic lengths. There was a high level of correlation among life‐history traits across species. Relationships between length‐based and age‐based variables were weakest, with a tenuous link between maximum body size and life span. Cluster analysis based on similarities among life‐history traits demonstrated that species were significantly grouped at two major levels. The first grouping was driven by length‐based variables (lengths at maturity and sex change and maximum length) and separated the small‐ and large‐bodied species. Within these, species were grouped by age‐based variables (age at maturity, mortality and life span). Groupings based on demographic and life‐history features were independent of phylogenetic relationships at the given taxonomic level. The results reiterate that body size is an important characteristic differentiating species, but interspecific variation in age‐based traits complicates its use as a life‐history proxy. Detailed life‐history metrics should facilitate future quantitative assessments of vulnerability to overexploitation in multispecies fisheries.     

Length–mass allometry in snakes

Body size and body shape are tightly related to an animal's physiology, ecology and life history, and, as such, play a major role in understanding ecological and evolutionary phenomena. Because organisms have different shapes, only a uniform proxy of size, such as mass, may be suitable for comparisons between taxa. Unfortunately, snake masses are rarely reported in the literature. On the basis of 423 species of snakes in 10 families, we developed clade‐specific equations for the estimation of snake masses from snout–vent lengths and total lengths. We found that snout–vent lengths predict masses better than total lengths. By examining the effects of phylogeny, as well as ecological and life history traits on the relationship between mass and length, we found that viviparous species are heavier than oviparous species, and diurnal species are heavier than nocturnal species. Furthermore, microhabitat preferences profoundly influence body shape: arboreal snakes are lighter than terrestrial snakes, whereas aquatic snakes are heavier than terrestrial snakes of a similar length. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ●● , ●●–●●.     

Bioclimatic evaluation of geographical range in Fragaria (Rosaceae): consequences of variation in breeding system,ploidy and species age

The evaluation of the intrinsic and extrinsic forces that determine geographical range sizes and niche breadth is key to the understanding of species distributions and for informing the conservation of biodiversity. Fragaria (Rosaceae) contains the economically important cultivated strawberry (Fragaria × ananassa subsp. ananassa) and numerous wild species. Using georeferenced species records and global bioclimatic data, we describe the bioclimatic niches for 21 Fragaria spp. and investigate the relationship between their niches and geographical range size, breeding system, ploidy and time since divergence. We found no evidence of phylogenetic signal for bioclimatic niches. There was also no relationship between ploidy and geographical or bioclimatic range area, but geographical range area was significantly greater for species that were capable of self‐fertilization. In addition, we found a significant decelerating relationship between species age and geographical range area. Overall, our results suggest that Fragaria spp., although similar in morphology and life history, show high levels of divergence in bioclimatic niches and significant over‐dispersion along some bioclimatic gradients, suggesting evolutionary lability in physiology and climate tolerance. As a consequence, wild species will remain a valuable resource for cultivated strawberry sustainability, especially under changing future climate. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176 , 99–114.     

Global gradients of avian longevity support the classic evolutionary theory of ageing

Senescence, the process of physiological deterioration associated with growing old, is a shared characteristic of a wide range of animals. Yet, lifespan varies dramatically among species. To explain this variation, the evolutionary theory of ageing has been proposed more than 50 yr ago. Although the theory has been tested experimentally and through comparative analyses, there remains debate whether its fundamental prediction is empirically supported. Here, we use a comprehensive database on avian life history traits to test the evolutionary theory of ageing at a global scale. We show that pronounced geographical gradients of maximum longevity exist, that they are predicted by measures of predator diversity and only partly depend on correlated life‐history traits. The results are consistent with species‐level analyses and can be replicated across bio‐geographical regions. Our analyses suggest that stochastic predation is an important driver of the evolution of lifespan, at least in birds.     

The interplay of dispersal limitation,rivers, and historical events shapes the genetic structure of an Amazonian frog

Disentangling the impact of landscape features such as rivers and historical events on dispersal is a challenging but necessary task to gain a comprehensive picture of the evolution of diverse biota such as that found in Amazonia. Adenomera andreae, a small, territorial, terrestrial frog species of the Amazonian forest represents a good model for such studies. We combined cytochrome b sequences with 12 microsatellites to investigate the genetic structure at two contrasted spatial scales in French Guiana: along a ～6‐km transect, to evaluate dispersal ability, and between paired bank populations along a ～65‐km stretch of the Approuague river, to test the effect of rivers as barriers to dispersal. We observed significant spatial genetic structure between individuals at a remarkably small geographical scale, and conclude that the species has a restricted dispersal ability that is probably tied to its life‐history traits. Mitochondrial and microsatellite data also indicate a high level of differentiation among populations on opposite banks of the river, and, in some cases, among populations on the same riverbank. These results suggest that the observed population structure in A. andreae is the result of restricted dispersal abilities combined with the action of rivers and Quaternary population isolation. Given that Amazonia hosts a great portion of anurans, as well as other small vertebrates, that display life‐history traits comparable with A. andreae, we argue that our analyses provide new insights into the complex interactions among evolutionary processes shaping Amazonian biodiversity. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 356–373.     

The roles of pre‐ and post‐hatching growth rates in generating a latitudinal cline of body size in the eastern fence lizard (Sceloporus undulatus)

Countergradient variation in norms of reaction can dampen the direct effects of environmental influences on phenotypic traits, allowing phenotypic similarity among populations despite exposure to different environmental conditions. Such norms of reaction may occur at any phase of the life‐history (e.g. growth rates during both embryonic and postembryonic stages may influence geographical variation in adult body size). We collected gravid female lizards (Sceloporus undulatus) from northern (Indiana), central (Mississippi), and southern (Florida) populations, spanning almost the full latitudinal range of the species. Adult females from the southern population were smaller. Intrinsic growth rates of hatchlings were higher for the central population than for the other two populations. This pattern does not parallel the countergradient variation previously found in embryonic developmental rates among these populations. Earlier hatching enhanced survival rates of juveniles to a similar degree among populations, although juvenile survival rates in the field generally increase with latitude in this species. Our data reveal geographical variation in the ways in which intrinsic developmental/growth rates and survival shift during ontogeny, and suggest that latitudinal patterns in adult body size (such as Bergmann's rule) can result from both faster growth, and longer periods of growth. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 202–209.     

The response of life‐history traits to a new species in the community: a story of Drosophila parasitoids from the Rhône and Saône valleys

In the present study, we investigated the evolution of life‐history traits in the main species of a community, after the arrival of a new competitor. Two parasitoid species, Leptopilina heterotoma and Asobara tabida, are present throughout the Rhône and Saône valleys, whereas a third species, Leptopilina boulardi, is slowly extending its distribution northwards. In the presence of L. boulardi, competing parasitoids experience a higher mortality and lower host availability. Resources should thus be re‐allocated between traits according to these new factors. We compared life‐history traits of populations of L. heterotoma and A. tabida in areas with and without L. boulardi. As predicted by both Price's balanced mortality hypothesis and the theory of life‐history traits, we found that investment in reproduction is higher in southern populations for both native species, coupled with higher travelling abilities. However, only A. tabida paid their higher fecundity by a lower longevity. The absence of a clear trade‐off between these traits in L. heterotoma may be explained by a lower metabolic rate in southern populations. These results highlight the importance of the community change over climate in the evolution of life‐history traits in this parasitoid community. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Adaptive radiation in miniature: the minute salamanders of the Mexican highlands (Amphibia: Plethodontidae: Thorius)

The small size and apparent external morphological similarity of the minute salamanders of the genus Thorius have long hindered evolutionary studies of the group. We estimate gene and species trees within the genus using mitochondrial and nuclear DNA from nearly all named and many candidate species and find three main clades. We use this phylogenetic hypothesis to examine patterns of morphological evolution and species coexistence across central and southern Mexico and to test alternative hypotheses of lineage divergence with and without ecomorphological divergence. Sympatric species differ in body size more than expected after accounting for phylogenetic relationship, and morphological traits show no significant phylogenetic signal. Sympatric species tend to differ in a combination of body size, presence or absence of maxillary teeth, and relative limb or tail length, even when they are close relatives. Sister species of Thorius tend to occupy climatically similar environments, which suggests that divergence across climatic gradients does not drive species formation in the genus. Rather than being an example of cryptic species formation, Thorius more closely resembles an adaptive radiation, with ecomorphological divergence that is bounded by organism‐level constraints. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 622–643.     

Evolutionary genetics of Drosophila ananassae: evidence for trade-offs among several fitness traits

Correlated responses to bi‐directional selection on thorax length, examined on several life‐history traits and chromosome inversion polymorphisms, have revealed apparent novel trade‐offs in Drosophila ananassae. We provide evidence of trade‐offs between hatching time and pupal period, pupal period and egg‐pupa development time, and pupal period and larval development time (LDT). Body size shows positive correlations with ovariole number, LDT and DT (egg–fly). We provide evidence of sexual dimorphism for trade‐offs between longevity and body size and starvation and longevity in females only. Trade‐offs between wing/thorax (W/T) ratio and longevity, W/T ratio and starvation, and DT (egg‐ fly) and longevity are evident in males only. Sexual dimorphism is also evident for inversion polymorphism with body size and longevity. A longevity assay suggests that low line females outlived high line females whereas high line males outlived low line males. The mean longevity in males is negatively correlated with the 2L‐ST and 3R‐ST arrangement frequencies whereas the 3L‐ST arrangement frequency is positively correlated with the mean longevity in males but opposite arrangements are found in females. Absolute starvation resistance is negatively correlated with 2L‐ST and 3R‐ST chromosome arrangements and results in a trade‐off between longevity and absolute starvation resistance in females. Analyses of fecundity, hatchability, and viabilities based on age intervals in both G₁₀ and G₁₃ suggest that the early reproduction is favoured in D. ananassae. The productivity percentage is highest in the high line and there is no effect of late reproduction on it. Overall, we provide some unravelled trade‐offs and striking sex differences, which may help in understanding the life‐history evolution of the species. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 90 , 669–685.     

Macroecology and macroevolution of body size in Anolis lizards

Body size is one of the most influential traits affecting many ecological and physiological processes across animal and plant taxa. Studies of the environmental factors shaping body size patterns may evaluate either temporal or spatial dimensions. Here, we analyzed body size evolution in the radiation of Anolis lizards across both geographical and temporal dimensions. We used a set of macroecological and macroevolutionary methods to test current and past environmental effects on geographical gradients of body size and its evolutionary rates. First, we test whether a set of current ecological/physiological hypotheses (heat balance, productivity and seasonality) explains spatial body size gradients. Second, we evaluate how tempo (i.e. evolutionary rates) and mode (i.e. evolutionary process) of body size evolution changed through time and the role of paleo-temperatures on rates of body size evolution during the Cenozoic. We did not find a signature of current environmental variables driving spatial body size gradients. By contrast, we found strong support for a correlation between temperature changes (i.e. climate cooling) during the Cenozoic and rates of body size evolution (i.e. body size diversification). We suggest that patterns of body size evolution in Anolis lizards might be influenced by thermoregulatory behavior across clades and regions.     

A unified framework for diversity gradients: the adaptive trait continuum

Aim Adaptive trait continua are axes of covariation observed in multivariate trait data for a given taxonomic group. These continua quantify and summarize life‐history variation at the inter‐specific level in multi‐specific assemblages. Here we examine whether trait continua can provide a useful framework to link life‐history variation with demographic and evolutionary processes in species richness gradients. Taking an altitudinal species richness gradient for Mediterranean butterflies as a study case, we examined a suite of traits (larval diet breadth, adult phenology, dispersal capacity and wing length) and species‐specific habitat measures (temperature and aridity breadth). We tested whether traits and species‐specific habitat measures tend to co‐vary, whether they are phylogenetically conserved, and whether they are able to explain species distributions and spatial genetic variation in a large number of butterfly assemblages. Location Catalonia, Spain. Methods We formulated predictions associated with species richness gradients and adaptive trait continua. We applied principal components analyses (PCAs), structural equation modelling and phylogenetic generalized least squares models. Results We found that traits and species‐specific habitat measures covaried along a main PCA axis, ranging from multivoltine trophic generalists with high dispersal capacity to univoltine (i.e. one generation per year), trophic specialist species with low dispersal capacity. This trait continuum was closely associated with the observed distributions along the altitudinal gradient and predicted inter‐specific differences in patterns of spatial genetic variability (F_ST and genetic distances), population responses to the impacts of global change and local turnover dynamics. Main conclusions The adaptive trait continuum of Mediterranean butterflies provides an integrative and mechanistic framework to: (1) analyse geographical gradients in species richness, (2) explain inter‐specific differences in population abundances, spatial distributions and demographic trends, (3) explain inter‐specific differences in patterns of genetic variation (F_ST and genetic distances), and (4) study specialist–generalist life‐history transitions frequently involved in butterfly diversification processes.     

Testing the abundant‐centre hypothesis using intertidal porcelain crabs along the Chilean coast: linking abundance and life‐history variation

Aim The abundant‐centre hypothesis (ACH) is based on the assumption that physiological constraints limit populations at the edges of their distributional range, yet the geographical variation of physiological performance or life‐history traits has rarely been examined. Here we examine the applicability of the ACH in a marine system by testing whether physiological predictions are reflected in large‐scale variations of life‐history traits. Location The Chilean coast (18°–42° S), encompassing more than 2500 km along the Pacific coast of South America. Methods Five porcelain crab species (Petrolisthes granulosus, Petrolisthes laevigatus, Petrolisthes tuberculatus, Petrolisthes violaceus and Allopetrolisthes angulosus) were sampled on intertidal boulder beaches at 13 sampling sites. For each species and site we evaluated: (1) relative abundance (density), (2) maximum size, (3) size at maturity, (4) sex ratio, (5) proportion of ovigerous females, and (6) presence of recruits. The shape of the spatial distribution of each trait was evaluated statistically against the prediction of four hypothetical models (normal, ramped‐south, ramped‐north and abundant‐edge). Results The relative abundance and life‐history traits showed different spatial patterns among species. Relative abundance (across sites) was fitted by a normal model in only two species. No model fitted the spatial variation in body size and size at first maturity, which showed a slight but monotonic poleward increase in all species. Sex ratio showed a prominent hump‐shaped pattern, with females prevailing in the centre of the ranges and males dominating towards the range boundaries; this pattern was statistically significant in three of the five studied species. The proportion of ovigerous females showed no clear latitudinal trends, and mature individuals were observed across most of the geographical range of the species. However, recruits tended to be absent towards the southern (poleward) boundaries of the distribution. Main conclusions The ACH does not apply to all species equally. The link between abundance and life‐history traits is complex and variable among the porcelain crab species studied. Overall, the observed patterns were consistent with the idea that equatorward boundaries might be controlled by physiological restrictions mainly affecting adult survival, whereas poleward boundaries might be shaped by limitations in reproductive output and larval survival. Our results underline the importance of incorporating ecological, physiological and life‐history studies in future tests of the ACH.     

Testing historical explanations for gradients in species richness in heliconiine butterflies of tropical America

We compiled a large database of 58 059 point locality records for 70 species and 434 subspecies of heliconiine butterflies and used these data to test evolutionary hypotheses for their diversification. To study geographical patterns of diversity and contact zones, we mapped: (1) species richness; (2) mean molecular phylogenetic terminal branch length; (3) subspecies richness and the proportion of specimens that were subspecific hybrids, and (4) museum sampling effort. Heliconiine species richness is high throughout the Amazon region and peaks near the equator in the foothills and middle elevations of the eastern Andes. Mean phylogenetic terminal branch length is lowest in the eastern Andes and tends to be low in species‐rich areas. By contrast, areas of high subspecies richness, where subspecies overlap in range and/or hybridize, are concentrated along the course of the Amazon River, with the eastern Andes slopes and foothills relatively depauperate in terms of local intraspecific phenotypic diversity. Spatial gradients in heliconiine species richness in the Neotropics are consistent with the hypothesis that species richness gradients are driven at least in part by variation in speciation and/or extinction rates, resulting in observed gradients in mean phylogenetic branch length, rather than via evolutionary age or niche conservatism alone. The data obtained in the present study, coupled with individual case studies of recently evolved Heliconius species, suggest that the radiation of heliconiine butterflies occurred predominantly on the eastern slopes of the Andes in Colombia, Ecuador, and Peru, as well as in the upper/middle Amazon basin. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 479–497.     

Size‐induced phenotypic reaction norms in a parasitoid wasp: an examination of life‐history and behavioural traits

The amount of resources available during development often affects body size, causing phenotypic variation in life‐history traits and reproductive behaviours. However, past studies have seldom examined the reaction norms of both life‐history and behavioural traits versus body size. We measured the phenotypic plasticity of several life‐history (age‐specific egg load, egg size, longevity) and behavioural (oviposition rate, host marking rate, walking speed) traits of the egg parasitoid Telenomus podisi Ashmead (Hymenoptera: Scelionidae) in response to body size variation. We predicted that life‐history traits would show more evidence of size compensation than behavioural traits, resulting in fewer positively‐sloped size versus trait reaction norms among the former. As predicted by life‐history models, smaller wasps appear to shift resource allocation towards early‐life reproduction, having a similar egg load to large individuals 9 days after emergence. Surprisingly, longevity was unaffected by body size. However, egg size, the number of offspring produced during oviposition bouts, and the rate of subsequent egg synthesis were greater for larger individuals. In addition, as predicted, the reaction norms of behavioural traits versus body size were all positively sloped. Thus, despite possible adaptive compensatory plasticity of life‐history traits by small individuals, behavioural constraints directly related to body size would contribute to maintaining a positive size–fitness relationship.     

The role of disjunction and postglacial population expansion on phylogeographical history and genetic diversity of the circumboreal plant Chamaedaphne calyculata

In the last decade a number of studies has illustrated quite different phylogeographical patterns amongst plants with a northern present‐day geographical distribution, spanning the entire circumboreal region and/or circumarctic region and southern mountains. These works, employing several marker systems, have brought to light the complex evolutionary histories of this group. Here I focus on one circumboreal plant species, Chamaedaphne calyculata (leatherleaf), to unravel its phylogeographical history and patterns of genetic diversity across its geographical range. A survey of 29 populations with combined analyses of chloroplast DNA (cpDNA), internal transcribed spacer (ITS) and AFLP markers revealed structuring into two groups: Eurasian/north‐western North American, and north‐eastern North American. The present geographical distribution of C. calyculata has resulted from colonization from two putative refugial areas: east Beringia and south‐eastern North America. The variation of chloroplast DNA (cpDNA) and ITS sequences strongly indicated that the evolutionary histories of the Eurasian/north‐western North American and the north‐eastern North American populations were independent of each other because of a geographical disjunction in the distribution area and ice‐sheet history between north‐eastern and north‐western North America. Mismatch analysis using ITS confirmed that the present‐day population structure is the result of rapid expansion, probably since the last glacial maximum. The AFLP data revealed low genetic diversity of C. calyculata (P = 19.5%, H = 0.085) over the whole geographical range, and there was no evidence of loss of genetic diversity within populations in the continuous range, either at the margins or in formerly glaciated and nonglaciated regions. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 761–775.     

Plethodontid salamanders do not conform to "general rules" for ectotherm life histories: insights from allocation models about why simple models do not make accurate predictions

Recent theoretical models hold that temperature imposes unalterable physiological effects on ectotherm growth and development such that their life histories are dictated by local biophysical environments. Models relying on this premise have been offered to explain many life history phenotypes including threshold traits such as age/size at metamorphosis/maturity. Because threshold traits are thought to influence adult fitness components by affecting performance of an individual in its new habitat, they are evolutionarily important components of complex life cycles. Consequently, the ecological and genetical basis of variation in such traits has been the focus of a large research program by evolutionary biologists, and amphibians have been model systems for these studies in the last three decades. Smith‐Gill and Berven proposed a physiological model to explain commonly observed clinal patterns of variation in metamorphosis, and it appears to account successfully for patterns observed in a few species of pond‐breeding frogs and salamanders (Rana and Ambystoma). However, six species of stream‐breeding salamanders (family Plethodontidae: Desmognathus, Pseudotriton, Eurycea) contradict both the phenotypic patterns found in nature for pond‐breeding species as well as the predictions of this model. Four of the six species of plethodontids have significantly larger metamorphs at lower, warmer elevations (or more southerly latitudes) rather than at higher, cooler sites; two species show no clinal pattern. In light of these results, we critically examine the assumptions of and support for SGB. We propose alternative hypotheses to explain patterns of variation in metamorphic traits along thermal gradients, focusing on a) differences between pond‐breeding Amphibia and plethodontids in basic biology and larval habitats, b) gradients in other biotic and abiotic factors, and c) other effects of temperature on organismal function. Finally, we discuss our results in the context of current models of how ectotherm life histories are affected by temperature.