Taxa with large geographic distributions generally encompass diverse macroclimatic conditions, potentially requiring local adaptation and/or phenotypic plasticity to match their phenotypes to differing environments. These eco-evolutionary processes are of particular interest in organisms with traits that are directly affected by temperature, such as embryonic development in oviparous ectotherms. Here we examine the spatial distribution of fitness-related early-life phenotypes across the range of a widespread vertebrate, the painted turtle (Chrysemys picta). We quantified embryonic and hatchling traits from 7 locations (in Idaho, Minnesota, Oregon, Illinois, Nebraska, Kansas, and New Mexico) after incubating eggs under constant conditions across a series of environmentally relevant temperatures. Thermal reaction norms for incubation duration and hatchling mass varied among locations under this common-garden experiment, indicating genetic differentiation or pre-ovulatory maternal effects. However, latitude, a commonly-used proxy for geographic variation, was not a strong predictor of these geographic differences. Our findings suggest that this macroclimatic proxy may be an unreliable surrogate for microclimatic conditions experienced locally in nests. Instead, complex interactions between abiotic and biotic factors likely drive among-population phenotypic variation in this system. Understanding spatial variation in key life-history traits provides an important perspective on adaptation to contemporary and future climatic conditions.

Optimal maternal investment is often a tradeoff between conflicting pressures and varies depending upon environmental context and intrinsic female traits. Yet, offspring phenotype might also interact with such factors to influence investment. In aquatic turtles, terrestrial nests constructed farther from shore often have higher survival because nest predators tend to forage along environmental edges. However, offspring from eggs deposited farther inland must migrate farther to water upon emergence. We released hatchling common snapping turtles (Chelydra serpentina) at varying distances from a drift fence and monitored survival during overland dispersal. Survival decreased with dispersal distance and no selection on body size was evident for hatchlings dispersing from short- or intermediate-distances. However, survival increased with body size for hatchlings dispersing from the longest distance. Moreover, females producing larger and better dispersing offspring oviposited farther from water than females that produced smaller and poorer dispersing offspring. This conditional (on offspring body size) tradeoff suggests female investment can be sensitive to offspring phenotype and that such covariation between nest-site choice and offspring dispersal ability can maximize offspring survival and, thus, maternal fitness. Future work that considers the role of offspring performance on maternal behavior will elucidate an underappreciated influence of investment strategies.

1. The fitness consequence of maternal nest-site choice has attracted increasing scientific attention, but field studies identifying the long-term effects of nest-site choice on offspring survival and reproductive success are still rare in vertebrates. 2. To investigate the consequences of nest-site choice in lizards, we quantified the thermal and hydric conditions of nest sites that were chosen by female toad-headed agama (Phrynocephalus przewalskii) in the desert steppe of northern China. We also determined the effect of nest-site choice on embryonic development and survival and on offspring growth, survival, and maturity by comparing the embryos and offspring from maternally and randomly chosen nest sites. 3. We found that female toad-headed agama chose warm and moist nest sites that improved the developmental rate and survivorship of embryos and promoted the post-hatching growth, sexual maturity, reproduction, and fitness of offspring, thereby improving their reproductive success. 4. Such studies on short-lived lizards across multiple stages of embryonic and postembryonic ontogeny are critical for fully understanding the fitness consequences of nest-site choice.

The mechanisms that mediate the interaction between the thermal environment and species’ ranges are generally uncertain. Thermal environments may directly restrict species when environments exceed tolerance limits (i.e. the fundamental niche). However, thermal environments might also differentially affect relative performance among species prior to fundamental tolerances being met (i.e. the realized niche). We examined stress physiology (plasma glucose and corticosterone), mitochondrial performance, and the muscle metabolome of congeneric lizards that naturally partition the thermal niche, Elgaria multicarinata (southern alligator lizards; SAL) and E. coerulea (northern alligator lizards; NAL), in response to a thermal challenge to quantify variation in physiological performance and tolerance. Both NAL and SAL displayed physiological stress in response to high temperature, but neither showed signs of irreversible damage. NAL displayed a higher baseline mitochondrial respiration rate than SAL. Moreover, NAL substantially adjusted their physiology in response to thermal challenge whereas SAL did not. For example, the metabolite profile of NAL shifted with changes in key energetic molecules, whereas these were unaffected in SAL. Our results indicate that near-critical high temperatures should incur greater energetic cost in NAL than SAL via an elevated metabolic rate and changes to the metabolome. Thus, SAL displace NAL in warm environments that are within NAL's fundamental thermal niche, but relatively costly. Our results suggest that sub-critical thermal events can contribute to biogeographic patterns via physiological differences that alter the relative costs of living in warm or cool environments.

Globally, populations of diverse taxa have altered phenology in response to climate change. However, most research has focused on a single population of a given taxon, which may be unrepresentative for comparative analyses, and few long‐term studies of phenology in ectothermic amniotes have been published. We test for climate‐altered phenology using long‐term studies (10–36 years) of nesting behavior in 14 populations representing six genera of freshwater turtles (Chelydra, Chrysemys, Kinosternon, Malaclemys, Sternotherus, and Trachemys). Nesting season initiation occurs earlier in more recent years, with 11 of the populations advancing phenology. The onset of nesting for nearly all populations correlated well with temperatures during the month preceding nesting. Still, certain populations of some species have not advanced phenology as might be expected from global patterns of climate change. This collection of findings suggests a proximate link between local climate and reproduction that is potentially caused by variation in spring emergence from hibernation, ability to process food, and thermoregulatory opportunities prior to nesting. However, even though all species had populations with at least some evidence of phenological advancement, geographic variation in phenology within and among turtle species underscores the critical importance of representative data for accurate comprehensive assessments of the biotic impacts of climate change.

Lifespan and aging rates vary considerably across taxa; thus, understanding the factors that lead to this variation is a primary goal in biology and has ramifications for understanding constraints and flexibility in human aging. Theory predicts that senescence—declining reproduction and increasing mortality with advancing age—evolves when selection against harmful mutations is weaker at old ages relative to young ages or when selection favors pleiotropic alleles with beneficial effects early in life despite late-life costs. However, in many long-lived ectotherms, selection is expected to remain strong at old ages because reproductive output typically increases with age, which may lead to the evolution of slow or even negligible senescence. We show that, contrary to current thinking, both reproduction and survival decline with adult age in the painted turtle, Chrysemys picta, based on data spanning >20 y from a wild population. Older females, despite relatively high reproductive output, produced eggs with reduced hatching success. Additionally, age-specific mark–recapture analyses revealed increasing mortality with advancing adult age. These findings of reproductive and mortality senescence challenge the contention that chelonians do not age and more generally provide evidence of reduced fitness at old ages in nonmammalian species that exhibit long chronological lifespans.

Group formation is a common behaviour among prey species. In egg-laying animals, despite the various factors that promote intra-clutch variation leading to asynchronous hatching and emergence from nests, synchronous hatching and emergence occurs in many taxa. This synchrony may be adaptive by reducing predation risk, but few data are available in any natural system, even for iconic examples of the anti-predator function of group formation. Here, we show for the first time that increased group size (number of hatchlings emerging together from a nest) reduces green turtle (Chelonia mydas) hatchling predation. This effect was only observed earlier in the night when predation pressure was greatest, indicated by the greatest predator abundance and a small proportion of predators preoccupied with consuming captured prey. Further analysis revealed that the effect of time of day was due to the number of hatchlings already killed in an evening; this, along with the apparent lack of other anti-predatory mechanisms for grouping, suggests that synchronous emergence from a nest appears to swamp predators, resulting in an attack abatement effect. Using a system with relatively pristine conditions for turtle hatchlings and their predators provides a more realistic environmental context within which intra-nest synchronous emergence has evolved.

Comparative analyses of central molecular networks uncover variation that can be targeted by biomedical research to develop insights and interventions into disease. The insulin/insulin-like signaling and target of rapamycin (IIS/TOR) molecular network regulates metabolism, growth, and aging. With the development of new molecular resources for reptiles, we show that genes in IIS/TOR are rapidly evolving within amniotes (mammals and reptiles, including birds). Additionally, we find evidence of natural selection that diversified the hormone-receptor binding relationships that initiate IIS/TOR signaling. Our results uncover substantial variation in the IIS/TOR network within and among amniotes and provide a critical step to unlocking information on vertebrate patterns of genetic regulation of metabolism, modes of reproduction, and rates of aging.

Phenotypic variation is strongly impacted by environmental conditions experienced during development. Substantial laboratory research has shown that reptiles with flexible-shelled eggs are particularly sensitive to hydric conditions, yet research on nests in the wild is sparse. In this two-year field experiment, we explore the influence of hydric conditions during incubation on phenotypic traits of hatchling painted turtles (Chrysemys picta). Using a split-clutch design, we created two artificial nests adjacent to each maternally-selected nest site. Half the eggs incubated in a nest that received regular supplemental watering, while the control nest was exposed to natural precipitation only. Our results suggest that the influence of the hydric environment on developing reptilian embryos is context dependent. Supplemental water applied to nests in a drier than normal season elicited the expected biotic responses, based on laboratory experiments. However, when the soil surrounding C. picta eggs was already highly moist, the additional water from supplemental application effectively stunted embryonic development. Our experiment confirms that hydric conditions of the soil during incubation in the wild can substantially influence phenotypic variation of reptiles with flexible-shelled eggs. Additionally, our experiment highlights the importance of complex interactions in the field that are often unexplored in laboratory experiments, reiterating the importance of validating laboratory work with field experiments.

Offspring phenotypic variation can be substantially influenced by non-genetic factors such as maternal effects, which ultimately can influence organismal fitness. For oviparous organisms that lack parental care, oviposition-site choice and egg size are maternal effects that can greatly affect offspring traits. Yet, few studies examine the consequences of these traits in the wild. We manipulated the contents of natural painted turtle nests such that offspring spent two life stages (incubation and hibernation) in either maternally-selected nest sites or randomly-selected nest sites, and quantified treatment differences in environmental parameters and offspring phenotypes. Additionally, we tracked the fates of individual eggs and hatchlings, which allowed us to quantify the strength and form of selection acting on egg size during incubation and, for the first time, body size during hibernation. Maternally-selected nest sites were warmer and produced offspring that were longer and hatched earlier than their siblings emerging from cooler, randomly-selected nests. Treatments did not affect any measured traits during hibernation. We detected no selection on egg size during the incubation stage, but significant linear selection favoring larger hatchlings during hibernation. Our results suggest that nest-site choice allows mothers to partially control the environment of their incubating eggs, but is less effective at controlling hatchling environments during hibernation. Additionally, we provide novel support for the “bigger-is-better” hypothesis in turtles by showing a positive relationship between size and survival during the hibernation stage.