Adult Sex-Ratio Bias Does Not Lead to Detectable Adaptive Offspring Sex Allocation Via Nest-Site Choice in a Turtle With Temperature-Dependent Sex Determination.

Sex-ratio theory predicts that parents can optimise their fitness by producing offspring of the rare sex, yet there is a dearth of empirical evidence for adaptive sex allocation in response to the adult sex ratio (ASR). This is concerning, as anthropogenic disruption of the sex ratios of reproductive individuals threatens to cause demographic collapse in animal populations. Species with environmental sex determination (ESD) are especially at risk but may possess the capacity to adaptively influence offspring sex via control over the developmental environment.

Developmental Thermal Reaction Norms of Leatherback Marine Turtles at Nesting Beaches.

Accurate scientific information is critical for undertaking appropriate conservation and management practices for imperiled species. One source of concern is that research findings might vary for non-biological reasons, including experimental design and analytical methods. To illustrate, we provide detailed modern analysis of reproductive data for leatherback turtles ().

Increased nest temperature during winter does not affect residual yolk metabolism of hatchling painted turtles (Chrysemys picta).

Rising global temperatures have a wide range of effects at organismal, population, and ecosystem levels. Increased winter temperatures are expected to alter the energetics of species that are dormant during this time. Hatchling painted turtles (Chrysemys picta) spend their first ∼8 months in shallow nests on land, where they putatively rely on residual yolk reserves to fuel energetic demands during this period of inactivity before they emerge in the spring.

Geographic variation in incubation temperatures promoting viable offspring production in broadly co-distributed turtles.

Organisms whose early life stages are environmentally sensitive produce offspring within a relatively narrow range of suitable abiotic conditions. In reptiles, development rate and survival are often maximized if incubation temperatures remain under 31°C, though this upper bound may vary within and among species. We addressed this expectation by comparing responses to egg incubation at 30°C versus 33°C in congeneric turtle species pairs with broad syntopic geographic distributions.

Demographic history and genomic signatures of selection in a widespread vertebrate ectotherm.

Environmental conditions vary greatly across large geographic ranges, and yet certain species inhabit entire continents. In such species, genomic sequencing can inform our understanding of colonization history and the impact of selection on the genome as populations experience diverse local environments. As ectothermic vertebrates are among the most vulnerable to environmental change, it is critical to understand the contributions of local adaptation to population survival.

Mother knows best: nest-site choice homogenizes embryo thermal environments among populations in a widespread ectotherm.

Species with large geographical ranges provide an excellent model for studying how different populations respond to dissimilar local conditions, particularly with respect to variation in climate. Maternal effects, such as nest-site choice greatly affect offspring phenotypes and survival. Thus, maternal behaviour has the potential to mitigate the effects of divergent climatic conditions across a species' range.

On the origin of patterns of temperature-dependent sex determination.

Species with temperature-dependent sex determination (TSD) exhibit significant variation in the relationship between incubation temperatures and the sex ratios they produce, making this an ideal system for comparing processes producing variation above and below the species level. Furthermore, a deeper mechanistic understanding of TSD macro- and microevolution may help reveal the currently unknown adaptive significance of this variation or of TSD as a whole. Here, we probe these topics by examining the evolutionary dynamics of this sex-determining mechanism in turtles.

Effects of the egg incubation environment on turtle carapace development.

Developing organisms are often exposed to fluctuating environments that destabilize tissue-scale processes and induce abnormal phenotypes. This might be common in species that lay eggs in the external environment and with little parental care, such as many reptiles. In turtles, morphological development has provided striking examples of abnormal phenotypic patterns, though the influence of the environment remains unclear.

ROSIE, a database of reptilian offspring sex ratios and sex-determining mechanisms, beginning with Testudines.

In contrast to genotypic sex determination (GSD), temperature-dependent sex determination (TSD) in amniotic vertebrates eludes intuitive connections to Fisherian sex-ratio theory. Attempts to draw such connections have driven over 50 years of research on the evolution of sex-determining mechanisms (SDM), perhaps most prominently among species in the order Testudines. Despite regular advancements in our understanding of this topic, no efforts have been published compiling the entirety of data on the relationships between incubation temperature and offspring sex in any taxonomic group.

Age Predicts Risky Investment Better Than Residual Reproductive Value.

AbstractLife-history theory predicts that investment in reproduction should increase as future reproductive potential (i.e., residual reproductive value [RRV]) decreases.

Predicting the effects of climate change on incubation in reptiles: methodological advances and new directions.

The unprecedented advancement of global climate change is affecting thermal conditions across spatial and temporal scales. Reptiles with temperature-dependent sex determination (TSD) are uniquely vulnerable to even fine-scale variation in incubation conditions and are a model system for investigating the impacts of shifting temperatures on key physiological and life-history traits. The ways in which current and predicted future climatic conditions translate from macro- to ultra-fine scale temperature traces in subterranean nests is insufficiently understood.

Becoming creatures of habit: Among- and within-individual variation in nesting behaviour shift with age.

The quantification of repeatability has enabled behavioural and evolutionary ecologists to assess the heritable potential of traits. For behavioural traits that vary across life, age-related variation should be accounted for to prevent biasing the microevolutionary estimate of interest. Moreover, to gain a mechanistic understanding of ontogenetic variation in behaviour, among- and within-individual variance should be quantified across life.

Insights from Population Genomics to Enhance and Sustain Biological Control of Insect Pests.

Biological control-the use of organisms (e.g., nematodes, arthropods, bacteria, fungi, viruses) for the suppression of insect pest species-is a well-established, ecologically sound and economically profitable tactic for crop protection.

Development-specific transcriptomic profiling suggests new mechanisms for anoxic survival in the ventricle of overwintering turtles.

Oxygen deprivation swiftly damages tissues in most animals, yet some species show remarkable abilities to tolerate little or even no oxygen. Painted turtles exhibit a development-dependent tolerance that allows adults to survive anoxia approximately four times longer than hatchlings: adults survive ∼170 days and hatchlings survive ∼40 days at 3°C. We hypothesized that this difference is related to development-dependent differences in ventricular gene expression.

Joint estimation of growth and survival from mark-recapture data to improve estimates of senescence in wild populations.

Understanding age-dependent patterns of survival is fundamental to predicting population dynamics, understanding selective pressures, and estimating rates of senescence. However, quantifying age-specific survival in wild populations poses significant logistical and statistical challenges. Recent work has helped to alleviate these constraints by demonstrating that age-specific survival can be estimated using mark-recapture data even when age is unknown for all or some individuals.

Do Covariances Between Maternal Behavior and Embryonic Physiology Drive Sex-Ratio Evolution Under Environmental Sex Determination?

Fisherian sex-ratio theory predicts sexual species should have a balanced primary sex ratio. However, organisms with environmental sex determination (ESD) are particularly vulnerable to experiencing skewed sex ratios when environmental conditions vary. Theoretical work has modeled sex-ratio dynamics for animals with ESD with regard to 2 traits predicted to be responsive to sex-ratio selection: 1) maternal oviposition behavior and 2) sensitivity of embryonic sex determination to environmental conditions, and much research has since focused on how these traits influence offspring sex ratios.

Geographic variation in thermal sensitivity of early life traits in a widespread reptile.

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 ().

Delayed trait development and the convergent evolution of shell kinesis in turtles.

Understanding developmental processes is foundational to clarifying the mechanisms by which convergent evolution occurs. Here, we show how a key convergently evolving trait is slowly 'acquired' in growing turtles. Many functionally relevant traits emerge late in turtle ontogeny, owing to design constraints imposed by the shell.

Environmentally induced phenotypic plasticity explains hatching synchrony in the freshwater turtle Chrysemys picta.

Environmentally cued hatching allows embryos to alter the time of hatching in relation to environment through phenotypic plasticity. Spatially variable temperatures within shallow nests of many freshwater turtles cause asynchronous development of embryos within clutches, yet neonates still hatch synchronously either by hatching early or via metabolic compensation. Metabolic compensation and changes in circadian rhythms presumably enable embryos to adjust their developmental rates to catch up to more advanced embryos within the nest.

Gene network variation and alternative paths to convergent evolution in turtles.

Diversification of the turtle's shell comprises remarkable phenotypic transformations. For instance, two divergent species convergently evolved shell-closing systems with shoulder blade (scapula) segments that enable coordinated movements with the shell. We expected these unusual structures to originate via similar changes in underlying gene networks, as skeletal segment formation is an evolutionarily conserved developmental process.

Altered spring phenology of North American freshwater turtles and the importance of representative populations.

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 (, , , , , and ).

Quantifying the effects of embryonic phenotypic plasticity on adult phenotypes in reptiles: A review of current knowledge and major gaps.

Studies of reptiles have contributed greatly to understanding the impacts of developmental environments on offspring phenotypes. A major challenge for these studies, however, is quantifying the effects of embryonic environments on adult phenotypes and reproductive success. Such measurements may be necessary to gain full insight into the evolution of plasticity, as well as the long-term consequences of plasticity under environmental change.