Incubation Temperature and Maternal Resource Provisioning, but Not Contaminant Exposure, Shape Hatchling Phenotypes in a Species with Temperature-Dependent Sex Determination

Abstract

chlorodiphenyldichloroethylene exposure did not generally affect hatchling traits, constant and fluctuating temperatures produced diverse phenotypic effects. Thermal fluctuations led to subtle changes in incubation duration and produced shorter hatchlings with smaller heads when compared to the constant temperature control. Warmer, male-promoting incubation temperatures resulted in larger hatchlings with more residual yolk reserves when compared to cooler, female-promoting temperatures. Together, these findings advance our understanding of how complex environmental factors interact with developing organisms to generate phenotypic variation and raise questions regarding the mechanisms connecting variable thermal conditions to responses in hatchling traits and their evolutionary implications for temperature-dependent sex determination.

Maternal provisioning interacts with incubation temperature to affect hatchling mercury exposure in an oviparous reptile

“…The influence of incubation temperature on contaminant body burdens in reptiles has hereto been unexplored, and our findings present the possibility that other aspects of the developmental environment may have additional effects, with downstream impacts on sex and/or size specific mortality. Incubation at FPT produces smaller hatchlings compared to incubation at MPT [19]. This reduction in hatchling mass is thought to result from increases in the energetic cost of development at FPT, with more maternal resources expended on metabolic processes (versus somatic growth) required to complete development [19,58].…”

“…Incubation at FPT produces smaller hatchlings compared to incubation at MPT [19]. This reduction in hatchling mass is thought to result from increases in the energetic cost of development at FPT, with more maternal resources expended on metabolic processes (versus somatic growth) required to complete development [19,58]. Thus, elevated THg concentrations in FPT hatchlings could be due to maternally deposited mercury representing a higher proportion of hatchling mass in smaller individuals.…”

“…THg concentration was log-transformed prior to model building; model residuals were checked for normality (Shapiro–Wilk test) and plotted to visually assess homoscedasticity. To determine factors influencing the distribution of mercury within hatchling tissues, we built predictive linear models for each tissue type incorporating clutch-averaged THg concentrations in egg yolk (reflective of initial maternally transferred mercury burdens), incubation treatment (reflective of differing metabolic rates [19]), and clutch-averaged hatchling mass (which could affect THg concentrations via a biodilution effect [44]). Full models and all possible iterations were ranked using AICc model selection using the ‘dredge’ function in the package ‘MuMIn’ [56], and results for all supported models (ΔAICc < 2) are reported.…”

“…In many non-mammalian vertebrates, the thermal environment experienced by developing embryos influences hatchling phenotypes and, in some cases, sex [17,18]. In the American alligator (Alligator mississippiensis), a species with temperature-dependent sex determination (TSD), warmer incubation temperatures (32.5-33.5°C) result in male development and more efficient conversion of maternal resources into hatchling mass compared to cooler, female-promoting temperatures (29-31°C) [19][20][21]. Temperature is known to affect toxicity of external contaminants in developing fish [22] and amphibian [23] eggs, but this phenomenon has not been examined in developing reptiles or in the context of maternally transferred contaminants.…”

Phenotypic plasticity as a facilitator of microbial evolution

“…A classic example is the epigenetic differentiation of pluripotent stem cells [ 53 ]; this differentiation is reversible via epigenetic reprogramming, although interestingly, some epigenetic marks can escape this process [ 54 ]. Exotic examples of this process include epigenetically driven temperature-dependent sex determination in a variety of reptiles [ 55 , 56 ]. More controversially, cellular and organismal aging could be viewed as an extreme example of an epigenetically encoded state, as there are distinct chromatin availability features in aged cells [ 57 ].…”