Life History Variation Research Articles

Pedigree Analysis of an Integrated Hatchery Steelhead Program from the Mad River, California, Provides Insight into Life History Patterns and Informs Management

AbstractThe Mad River Hatchery supports one of the most important fisheries for steelhead Oncorhynchus mykiss in California. Although the Mad River Hatchery has stated goals of operating an integrated hatchery program that addresses demographic and genetic risks, very little monitoring of these goals has taken place. We applied parentage‐based tagging methods to assess the origin (wild versus hatchery), age structure, and spawn‐date heritability of steelhead returning to the Mad River Hatchery. We generated single nucleotide polymorphism genotypes at 96 loci for all adult steelhead broodstock spawned at Mad River Hatchery over a 9‐year period (2009–2017; N = 1,572) and identified 965 trios (mother, father, and offspring) using parentage analysis. Although the hatchery attempts to release 100% adipose‐fin‐clipped hatchery steelhead, our analysis uncovered a large difference in the proportion of hatchery‐origin broodstock individuals as estimated by pedigrees (0.87) and traditional adipose fin clipping (0.58). This difference presumably resulted from failure to clip or identify a clip in 100% of hatchery‐produced fish. Our analysis revealed the complete age structure of six cohorts of hatchery broodstock and showed substantial differences in different years for Mad River Hatchery steelhead. Pedigree‐based estimates of narrow‐sense heritability for spawn date were 0.242 to 0.470, indicating moderate to high heritability, and highlighting the opportunity for a strong response to selection on this trait imposed by hatchery spawning. The application of parentage‐based tagging provided critical information for understanding life history variation and the efficacy of management actions for Mad River Hatchery steelhead and provides a framework for minimizing domestication selection and associated reductions in fitness for naturally spawning fish in this integrated population.

Life history variation between two Eurasian tree sparrow Passer montanus populations at different altitudes

Abstract Altitudinal gradients create environmental variation that can strongly affect avian life history strategies. To fully understand this issue, a comparison of the demography of populations of the same species over large altitudinal differences is required. Here, we investigated the breeding ecology of two populations of Eurasian tree sparrow (Passer montanus), one in the temperate zone of central China at an altitude of 30 m and another in the alpine zone of the northeastern Tibetan plateau at an altitude of 3430 m. The breeding ecology of this species was rarely studied at such a high altitude before. Our result revealed that high-altitude tree sparrows started breeding later, had a shorter breeding period (80 versus 140 days), produced smaller broods (1.2 versus 2.5 chicks) and had significantly smaller clutches (4.0 versus 4.9 eggs) but larger eggs (4272 versus 3443 mm3) when compared with their low-altitude counterparts. Besides, tree sparrows at our high-altitude site had longer nestling periods (14.5 versus 13.4 days) than those at the low-altitude site. High-altitude tree sparrows tend to have reduced fecundity but allocate more energy into each offspring to confront the stressful conditions at high altitudes. The observed patterns are consistent with adaptive life history strategies.

Determinants of genetic diversity and species richness of North American amphibians

AbstractAimEcological limits on population sizes and the number of species a region can sustain are thought to simultaneously produce spatial patterns in population genetic diversity and species richness due to the effects of random drift operating in parallel across population and community levels. Here, we test the extent to which resource‐based environmental limits jointly determine these patterns of biodiversity in amphibians.LocationNorth America.TaxonAmphibians.MethodsWe repurposed open, raw microsatellite data from 19 species sampled at 554 sites in North America and mapped nuclear genetic diversity at the continental scale. We then tested whether ecological limits defined by resource availability and environmental heterogeneity could simultaneously shape biogeographic patterns in genetic diversity and species richness with structural equation modelling.ResultsSpatial patterns of population genetic diversity run opposite patterns of species richness and genetic differentiation. However, while measures of resource availability and niche heterogeneity predict 89% of the variation in species richness, these landscape metrics were poor predictors of genetic diversity.Main conclusionsAlthough heterogeneity appears to be an important driver of genetic and species biodiversity patterns in amphibians, variation in genetic diversity both within and across species makes it difficult to infer general processes producing spatial patterns of amphibian genetic diversity. This result differs from those found in endotherms and may be due to the considerable life history variation found across amphibians.

Using relative brain size as predictor variable: Serious pitfalls and solutions.

There is a long‐standing interest in the effect of relative brain size on other life history variables in a comparative context. Historically, residuals have been used to calculate these effects, but more recently it has been recognized that regression on residuals is not good practice. Instead, absolute brain size and body size are included in a multiple regression, with the idea that this controls for allometry. I use a simple simulation to illustrate how a case in which brain size is a response variable differs from a case in which relative brain size is a predictor variable. I use the simulated data to test which modeling approach can estimate the underlying causal effects for each case. The results show that a multiple regression model with both body size and another variable as predictor variable and brain size as response variable work well. However, if relative brain size is a predictor variable, a multiple regression fails to correctly estimate the effect of body size. I propose the use of structural equation models to simultaneously estimate relative brain size and its effect on the third variable and discuss other potential methods.

Large mammal telomere length variation across ecoregions

BackgroundTelomere length provides a physiological proxy for accumulated stress in animals. While there is a growing consensus over how telomere dynamics and their patterns are linked to life history variation and individual experience, knowledge on the impact of exposure to different stressors at a large spatial scale on telomere length is still lacking. How exposure to different stressors at a regional scale interacts with individual differences in life history is also poorly understood. To better understand large-scale regional influences, we investigated telomere length variation in moose (Alces alces) distributed across three ecoregions. We analyzed 153 samples of 106 moose representing moose of both sexes and range of ages to measure relative telomere lengths (RTL) in white blood cells.ResultsWe found that average RTL was significantly shorter in a northern (montane) and southern (sarmatic) ecoregion where moose experience chronic stress related to severe summer and winter temperatures as well as high anthropogenic land-use compared to the boreal region. Our study suggests that animals in the northern boreal forests, with relatively homogenous land use, are less disturbed by environmental and anthropogenic stressors. In contrast, animals in areas experiencing a higher rate of anthropogenic and environmental change experience increased stress.ConclusionAlthough animals can often adapt to predictable stressors, our data suggest that some environmental conditions, even though predictable and ubiquitous, can generate population level differences of long-term stress. By measuring RTL in moose for the first time, we provide valuable insights towards our current understanding of telomere biology in free-ranging wildlife in human-modified ecosystems.

Resolving the deep phylogeny: Implications for early adaptive radiation, cryptic, and present-day ecological diversity of Papuan microhylid frogs

The microhylid frogs of the New Guinea region are the largest and most ecologically diverse subfamily (Asterophryinae) of one of the largest anuran families in the world and can live in communities of up to 20 species. While there has been recent progress in resolving the phylogenetic relationships of Asterophryinae, significant uncertainties remain, impeding further progress in understanding the evolution of microhabitat use, parental care, and life history variation in this group. In particular, the early divergences at the base of the tree remain unclear; as does the monophyly of some genera; and recent studies have discovered that species with wide geographic distribution are instead cryptic species complexes. In this study, we fortified geographic sampling of the largest previous phylogenetic effort by sequencing an additional 62 taxa and increased data quality and quantity by adding new layers of data vetting and by filling in previously incomplete loci to the five gene dataset (2 mitochondrial, 3 nuclear protein-coding genes) to obtain a dataset that is now 99% complete in over 2400 characters for 233 samples (205 taxa) of Asterophryinae and 3 outgroup taxa, and analyzed microhabitat use data for these taxa from field data and data collected from the literature. Importantly, our sampling includes complete community complements at 19 sites as well as representatives at over 80 sites across New Guinea and its offshore islands. We present a highly resolved molecular phylogeny which, for the first time, has over 95% of nodes supported (84% highly supported) whether using Maximum Likelihood or Bayesian Inference, allowing clarification of all genera (whether monophyletic or clearly not), their sister genera relationships, as well as an age estimate for the Asterophryinae at approximately 20MYA. Early generic diversification occurring between 17 and 12 MYA gave rise to a surprising diversity of about 18 genera as well as the 5 putative microhabitat types. Our tree reveals extensive cryptic diversity calling any widespread taxa into doubt, and clearly demonstrates that complex multispecies communities of Asterophryinae are ecologically diverse, are numerous, and of ancient origin across New Guinea. We discuss the implications of our phylogeny for explaining the explosive diversification of Asterophryinae as the result of adaptive radiation, niche conservatism, and non-adaptive radiation.

Development of DNA methylation-based epigenetic age predictors in loblolly pine (Pinus taeda).

Biological ageing is connected to life history variation across ecological scales and informs a basic understanding of age-related declines in organismal function. Altered DNA methylation dynamics are a conserved aspect of biological ageing and have recently been modelled to predict chronological age among vertebrate species. In addition to their utility in estimating individual age, differences between chronological and predicted ages arise due to acceleration or deceleration of epigenetic ageing, and these discrepancies are linked to disease risk and multiple life history traits. Although evidence suggests that patterns of DNA methylation can describe ageing in plants, predictions with epigenetic clocks have yet to be performed. Here, we resolve the DNA methylome across CpG, CHG, and CHH-methylation contexts in the loblolly pine tree (Pinus taeda) and construct epigenetic clocks capable of predicting ages in this species within 6% of its maximum lifespan. Although patterns of CHH-methylation showed little association with age, both CpG and CHG-methylation contexts were strongly associated with ageing, largely becoming hypomethylated with age. Among age-associated loci were those in close proximity to malate dehydrogenase, NADH dehydrogenase, and 18S and 26S ribosomal RNA genes. This study reports one of the first epigenetic clocks in plants and demonstrates the universality of age-associated DNA methylation dynamics which can inform conservation and management practices, as well as our ecological and evolutionary understanding of biological ageing in plants.

Herbarium specimens provide reliable estimates of phenological responses to climate at unparalleled taxonomic and spatiotemporal scales

Understanding the effects of climate change on the phenological structure of plant communities will require measuring variation in sensitivity among thousands of co‐occurring species across regions. Herbarium collections provide vast resources with which to do this, but may also exhibit biases as sources of phenological data. Despite general recognition of these caveats, validation of herbarium‐based estimates of phenological sensitivity against estimates obtained using field observations remains rare and limited in scope. Here, we leveraged extensive datasets of herbarium specimens and of field observations from the USA National Phenology Network for 21 species in the United States and, for each species, compared herbarium‐ and field‐based estimates of peak flowering dates expected under standardized temperature conditions, and of sensitivity of peak flowering time to geographic and interannual variation in mean minimum temperatures (TMIN). We found strong agreement between herbarium‐ and field‐based estimates for standardized peak flowering time (r = 0.91, p < 0.001) and for the direction and magnitude of sensitivity to both geographic TMIN variation (r = 0.88, p < 0.001) and interannual TMIN variation (r = 0.82, p < 0.001). This agreement was robust to substantial differences between datasets in 1) the long‐term TMIN conditions observed among collection and phenological monitoring sites and 2) the interannual TMIN conditions observed in the time periods encompassed by both datasets for most species. Our results show that herbarium‐based sensitivity estimates are reliable among species spanning a wide diversity of life histories and biomes, demonstrating their utility in a broad range of ecological contexts, and underscoring the potential of herbarium collections to enable phenoclimatic analysis at taxonomic and spatiotemporal scales not yet captured by observational data.

Intraspecific variation in Potamogeton illinoensis life history and seed germination has implications for restoration in eutrophic lakes

Intraspecific variation in Potamogeton illinoensis life history and seed germination has implications for restoration in eutrophic lakes

Nesting and post‐fledging predation risk influence diel patterns of songbird fledging

Among stages of avian ontogeny, the act of nest departure or fledging is an abrupt transition into a new environment and a major leap toward independence for offspring. In altricial birds, the timing (i.e. time of day) of fledging is notable in that many species tend to fledge early in the morning. Past studies have proposed nest predation as a key factor driving birds to fledge earlier in the morning (the ‘survival hypothesis’), whereby offspring avoid peak times of nest predation that occur later in the day. A natural extension of this hypothesis is the predation of offspring post‐fledging, whereby offspring are also timing their fledging with future survival prospects outside of the nest. However, few studies have investigated fledging behaviour in the context of both nesting and post‐fledging predation. To help fill this knowledge gap, we investigated factors driving the timing and duration of fledging across six songbird species in the context of offspring predation: daily nest mortality, post‐fledging mortality and diel patterns of nest predation risk. We found that > 60% of songbirds fledged early in the morning, whereas the peaks in nest predation risk occurred several hours post‐fledging. Furthermore, species under greater risk of nest predation fledged earlier in the day and in closer succession to their siblings. Parameters of post‐fledging mortality were poor predictors of fledging timing, but individuals from broods of species under higher risk of post‐fledging mortality fledged in closer succession to their siblings. These results provide evidence in support of the survival hypothesis, and suggest that songbirds fledge in the morning to avoid peak times of nest predation risk that occur later in the day (~ 8 h after civil dawn). Such results corroborate past research highlighting predation on dependent offspring as a key factor driving variation in life histories across animal taxa; however, estimates of post‐fledging mortality suggest that nest predation alone does not fully explain variation in fledging behaviour among species. Future research is therefore needed to investigate the contribution of other factors, such as energetics, parent–offspring conflict and diel patterns of post‐fledging survival, which may help to mediate diel patterns of fledging within and among songbird species.

Evolutionary Changes in the Chromatin Landscape Contribute to Reorganization of a Developmental Gene Network During Rapid Life History Evolution in Sea Urchins.

Chromatin configuration is highly dynamic during embryonic development in animals, exerting an important point of control in transcriptional regulation. Yet there exists remarkably little information about the role of evolutionary changes in chromatin configuration to the evolution of gene expression and organismal traits. Genome-wide assays of chromatin configuration, coupled with whole-genome alignments, can help address this gap in knowledge in several ways. In this study we present a comparative analysis of regulatory element sequences and accessibility throughout embryogenesis in three sea urchin species with divergent life histories: a lecithotroph Heliocidaris erythrogramma, a closely related planktotroph H. tuberculata, and a distantly related planktotroph Lytechinus variegatus. We identified distinct epigenetic and mutational signatures of evolutionary modifications to the function of putative cis-regulatory elements in H. erythrogramma that have accumulated nonuniformly throughout the genome, suggesting selection, rather than drift, underlies many modifications associated with the derived life history. Specifically, regulatory elements composing the sea urchin developmental gene regulatory network are enriched for signatures of positive selection and accessibility changes which may function to alter binding affinity and access of developmental transcription factors to these sites. Furthermore, regulatory element changes often correlate with divergent expression patterns of genes involved in cell type specification, morphogenesis, and development of other derived traits, suggesting these evolutionary modifications have been consequential for phenotypic evolution in H. erythrogramma. Collectively, our results demonstrate that selective pressures imposed by changes in developmental life history rapidly reshape the cis-regulatory landscape of core developmental genes to generate novel traits and embryonic programs.

A Female-Centered Evaluation of Growth, Survival, Reproduction, and Demography in the Salamander Desmognathus quadramaculatus

In the present report, I evaluate life history and demography for two populations of the Black-bellied Salamander, Desmognathus quadramaculatus, in the Cowee and Nantahala Mountains, North Carolina, using published data on growth of females, fecundity, and larval growth and development to generate life tables and metabolic life histories for each population. I assumed that females in these populations reproduce biennially, beginning at ages 7–8 years and 8–10 years in Cowee and Nantahala populations, respectively. In deriving life tables, I posited stationary populations wherein net reproductive rate (R0) equaled 1.0 and population growth rate (r) equaled 0. Fecundity (mx column of the life table) was based on counts of ovarian follicles in gravid females. Survival values (lx column of the life table) were generated by an iterative process that yielded a value of R0 = 1.0. I projected the life spans in each population to 25 years. The demographic models developed by the procedure allowed comparison with those reported earlier for D. monticola and D. ocoee. Age at first reproduction and generation time are key contributors to variation in body size and life history in Desmognathus.

Winter severity affects occupancy of spring‐ and summer‐breeding anurans across the eastern United States

AbstractAimClimate change is an increasingly important driver of biodiversity loss. The ectothermic nature of amphibians may make them particularly sensitive to changes in temperature and precipitation regimes, adding to declines from other threats. While active season environmental conditions can influence growth and survival, effects of variation in winter conditions on population dynamics are less well‐studied. Given that extreme winter temperatures can influence amphibian survival and fitness, we expected that increased winter severity—as measured by variability in winter temperatures and snow cover—would be associated with decreased occupancy, and that populations that experience more severe winters would have the largest sensitivities and show the greatest declines.LocationEastern United States.Time period2001–2015.Major taxa studiedAnurans.MethodsWe used large‐scale citizen science data from the eastern half of the United States, a diverse biogeographic and climatic region, to assess how variation in winter severity influenced occupancy dynamics (i.e. presence or absence of species across sites and years) of 11 spring and summer breeding anuran species.ResultsMost species had increased occupancy in years with greater than average snow cover and warmer than average mean winter temperatures. Surprisingly, climatic conditions in winter affected occupancy dynamics of species with varying life history characteristics, including both spring and summer breeding species, those that overwinter under the soil, and those that overwinter in ponds and stream beds. For two wide‐ranging species (Lithobates catesbeianus and Lithobates clamitans), colder winter temperatures reduced occupancy more at northern latitudes, while the association between days of snow cover and latitude was equivocal.Main conclusionsAs the climate continues to change, expected reductions in snowpack may reduce occupancy of already declining anuran populations, while milder winters may improve overwinter survival for some species. The contradictory impacts of temperature and snow cover illustrate the importance of considering multi‐dimensional impacts of climate change on anuran populations.

In-river behaviour and freshwater return rates of sea trout, Salmo trutta L., from two coastal river populations.

The effective management of anadromous Salmo trutta resources is challenging because long-term data on life history, phenology and survival are sparse and most stocks across the range are highly diverse and data-limited. The current study employed acoustic telemetry to tag 448 sea trout across three life stages, to describe the phenology, spawning behaviour and return rates of smolts, finnock (0+ sea age) and adult (≥1+ sea age) sea trout in two Irish river systems during 2018-2021. Tagged smolts (n=206) exhibited river to sea transition rates of 78%-92% and a number of surviving smolts returned to their natal river as 0+ sea age finnock, exhibiting overall smolt to finnock return rates of between 6% and 17%. Short-term vagrancy occurred among smolts, and 14 individuals were detected in adjacent non-natal rivers. Finnock tagged during the late summer (n=205) exhibited a range of behaviours with a minority (<30%) ascending upstream to spawning areas. Tagged adult sea trout (n=37) ascended upstream to the spawning grounds and between 50% and 80% successfully returned to sea as kelts after spawning. Subsequent return rates of kelts back to the river in the following year ranged from 9% to 40%. The current study indicated that body size was an influential predictor of behaviour and survival across all three life stages. Increased body size was positively associated with marine transition success in smolts, long-term marine survival in kelts and spawning behaviour in finnock. This work further demonstrates the complexity of sea trout life-history dynamics and provides a comparative perspective across different age classes. An understanding of life-history variation, behaviour and survival is fundamental for the successful management and conservation of sea trout stocks.

Benefits of measurable population connectivity metrics for area-based marine management

The dispersal of larvae by ocean currents is likely to represent an increasingly important driver of marine population dynamics across fragmented habitats. A boost in availability of larval dispersal data from biophysical simulations has therefore led to routine calculations of population connectivity metrics that are used for area-based management decision support, including the placement of Marine Protected Areas (MPAs). However, connectivity-based decision support for area-based management is often complex, highly uncertain, and the associated conservation impact rarely if ever evaluated. In combination, these challenges risk stakeholder engagement, compliance, and overall management effectiveness. Here we use a case study representing multiple key fishery species on coral reefs in Indonesia to demonstrate that consideration of larval dispersal for MPA placement decision support could be critical to recover both fish populations and fisheries from depletion, thereby mitigating potentially severe impacts on coastal communities. Importantly, we further show that MPA placement decisions can be effective even if based on comparatively simple and empirically measurable dispersal characteristics. Maximizing larval export, expressed as the contribution of larvae from MPA candidate sites to total larval settlement in surrounding areas, for example, was found to be a broadly beneficial MPA placement prioritization approach. Across investigated fish families with diverse life histories, this strategy resulted in MPA network designs that increased catches by a factor of 1.3 ± 0.3 (mean ± SD) and total fish biomass by a factor of 3.2 ± 0.3 (9.7 ± 1.2 in no-fishing areas and 1.4 ± 0.3 in fished areas) compared to conditions without effectively managed or protected areas. Our findings are relevant for both the implementation and impact evaluation of global marine conservation policies, specifically in tropical biodiversity hotspots, such as Indonesia, where coral reefs are often overfished and increasingly threatened but local communities highly dependent on sustainable fisheries.

The Pace of Life: Metabolic Energy, Biological Time, and Life History.

New biophysical theory and electronic databases raise the prospect of deriving fundamental rules of life, a conceptual framework for how the structures and functions of molecules, cells and individual organisms give rise to emergent patterns and processes of ecology, evolution and biodiversity. This framework is very general, applying across taxa of animals from 10-10 g protists to 108 g whales, and across environments from deserts and abyssal depths to rain forests and coral reefs. It has several hallmarks: 1) Energy is the ultimate limiting resource for organisms and the currency of biological fitness. 2) Most organisms are nearly equally fit, because in each generation at steady state they transfer an equal quantity of energy (22.4 kJ/g) and biomass (1 g/g) to surviving offspring. This is the equal fitness paradigm (EFP) of Brown et al. (2018). 3) The enormous diversity of life histories is due largely to variation in metabolic rates (e.g., energy uptake and expenditure via assimilation, respiration and production) and biological times (e.g., generation time). As in standard allometric and metabolic theory, most physiological and life history traits scale approximately as quarter-power functions of body mass, m (rates as ∼m-1/4 and times as ∼m1/4), and as exponential functions of temperature. 4) Time is the fourth dimension of life. Generation time is the pace of life. 5) There is, however, considerable variation not accounted for by the above scalings and existing theories. Much of this "unexplained" variation is due to natural selection on life history traits to adapt the biological times of generations to the clock times of geochronological environmental cycles. 7) Most work on biological scaling and metabolic ecology has focused on respiration rate. The emerging synthesis applies conceptual foundations of energetics and the EFP to shift the focus to production rate and generation time.

Life-history trait variation in native versus invasive asexual New Zealand mud snails.

Potamopyrgus antipodarum is a New Zealand freshwater snail that is invasive worldwide. While native P. antipodarum populations are characterized by frequent coexistence between obligately sexual and obligately asexual individuals, only the asexual snails are known to invade other ecosystems. Despitelow genetic diversity and the absence of sex, invasive asexual P. antipodarum are highly successful. Here, we quantified variation in three key life-history traits across invasive P. antipodarum lineages and compared this variation to already documented variation in these same traits in asexual native lineages to provide a deeper understanding of why some lineages become invasive. In particular, we evaluated if invasive lineages of P. antipodarum could be successful because they represent life-history variation from native ancestors that could facilitate invasion. We found that invasive snails displayed a non-representative sample of native diversity, with invasive snails growing more slowly and maturing more rapidly than their native counterparts. These results are consistent with expectations of a scenario where invasive lineages represent a subset of native variation that is beneficial in the setting of invasion. Together, these results help illuminate the mechanisms driving the worldwide expansion of invasive populations of these snails.

Thermoregulatory opportunity and competition act independently on life‐history traits in aquatic ectotherms

Abstract Many ectothermic species use behavioural thermoregulation to reduce their exposure to climate change. The buffering effect of behavioural thermoregulation will depend on the time available for an ectotherm to attain a body temperature within the target range, that is, the ‘opportunity for thermoregulation’. Behavioural thermoregulation can be further altered by the presence of competitors. Spatiotemporal dynamics in opportunity for thermoregulation and competition intensity should affect variation in ectotherm life history and fitness; however, experimental support for their joint influence is missing. I tested this prediction in a mesocosm experiment using larvae of two sympatric amphibians, the alpine newt Ichthyosaura alpestris and the common newt Lissotriton vulgaris. Thermoregulatory opportunities and competition intensities were manipulated by exposing larvae to warmer temperatures and altering densities of con‐ and heterospecifics. Life‐history traits were monitored until metamorphic emergence from the water. Thermoregulatory opportunity accelerated differentiation rate and time to metamorphic emergence, while both intra‐ and interspecific competition affected growth rate and mass at emergence. The impact of competition on survival and injury rates varied between taxa. Thermoregulatory opportunity and competition impacted larval life‐history traits in an additive fashion. Suitable conditions for thermoregulation allowed larvae to shorten their developmental period, and thus escape from the aquatic environment earlier than in thermoregulatory challenging environment. Competition was a primary determinant of mass at emergence, which is an important fitness correlate in amphibians. Species‐specific survival under competition may contribute to variation in habitat requirements between sympatric taxa. To sum up, predictions on the impact of climate change on ectotherm life histories require information not only about environmental temperatures, but also about species thermoregulatory opportunities and competitive abilities. Thermoregulatory opportunity is an ecologically relevant habitat property not only for basking ectotherms but also for taxa using less conspicuous thermoregulatory adjustments. The influence of thermoregulatory opportunity and competitive interactions on life histories varies among traits, indicating the need for a multi‐trait approach for understanding the complex influences of environmental change on ectotherm population dynamics and species interactions. Read the free Plain Language Summary for this article on the Journal blog.

Life history of spinyhead croaker Collichthys lucidus (Sciaenidae) differentiated among populations from Chinese coastal waters

Otolith microchemistry provides valuable information about the environmental history of individual fish, but few studies have considered the influence of population or stock on life history traits. This study used the Sr/Ca ratio as an index of habitat use of spinyhead croakerCollichthys lucidusfrom 2 different populations (northern and southern China populations), including lifetime otolith microchemistry profiles (n = 63 fish) and determinations of natal habitat selection (n = 352 fish). The otolith data revealed 3 life history patterns inC. lucidus: Pattern 1 individuals spent most of their lifetime (&gt;95%) in mesohaline waters (Sr/Ca range: 3-7 mmol mol-1), particularly during early growth; Pattern 2 individuals migrated from hyperhaline waters (Sr/Ca ≥ 7 mmol mol-1) to mesohaline waters; and Pattern 3 individuals migrated from oligohaline waters (Sr/Ca &lt; 3 mmol mol-1) to mesohaline waters. Pattern 2 and Pattern 3 were specific to the northern and southern China populations, respectively, and Pattern 1 was shared by the 2 populations. The otolith core Sr/Ca ratios showed that mostC. lucidusselected mesohaline waters as their natal habitat (i.e. 90.6% of 352 total individuals); 12.5% (19 of 152) selected hyperhaline waters and fell within the northern China population, and 7% (14 of 200) selected oligohaline waters and fell within the southern China population. These results indicate that life history diversity exists in this species, as the pattern of habitat use largely differed between the northern and southern China populations. The overall findings highlight that the behavior of different populations should be considered when determining fish migration histories.

Life-history genotype explains variation in migration activity in Atlantic salmon (Salmo salar).

One of the most well-known life-history continuums is the fast-slow axis, where 'fast' individuals mature earlier than 'slow' individuals. 'Fast' individuals are predicted to be more active than 'slow' individuals because high activity is required to maintain a fast life-history strategy. Recent meta-analyses revealed mixed evidence for such integration. Here, we test whether known life-history genotypes differ in activity expression by using Atlantic salmon (Salmo salar) as a model. In salmon, variation in Vgll3, a transcription cofactor, explains approximately 40% of variation in maturation timing. We predicted that the allele related to early maturation (vgll3*E) would be associated with higher activity. We used an automated surveillance system to follow approximately 1900 juveniles including both migrants and non-migrants (i.e. smolt and parr fish, respectively) in semi-natural conditions over 31 days (approx. 580 000 activity measurements). In migrants, but not in non-migrants, vgll3 explained variation in activity according to our prediction in a sex-dependent manner. Specifically, in females the vgll3*E allele was related to increasing activity, whereas in males the vgll3*L allele (later maturation allele) was related to increasing activity. These sex-dependent effects might be a mechanism maintaining within-population genetic life-history variation.