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Title: Incubation Temperature and Maternal Resource Provisioning, but Not Contaminant Exposure, Shape Hatchling Phenotypes in a Species with Temperature-Dependent Sex Determination
The environment experienced during embryonic development is a rich source of phenotypic variation, as environmental signals have the potential to both inform adaptive plastic responses and disrupt normal developmental programs. Environment-by-embryo interactions are particularly consequential for species with temperature-dependent sex determination, a mode of sex determination common in non-avian reptiles and fish, in which thermal cues during a discrete period of development drive the formation of either an ovary or a testis. Here we examine the impact of thermal variation during incubation in combination with developmental exposure to a common endocrine-disrupting contaminant on fitness-related hatchling traits in the American alligator (Alligator mississippiensis), a species with temperature-dependent sex determination. Using a factorial design, we exposed field-collected eggs to five thermal profiles (three constant temperatures, two fluctuating temperatures) and two environmentally relevant doses of the pesticide metabolite dichlorodiphenyldichloroethylene; and we quantified incubation duration, sex ratios, hatchling morphometric traits, and growth (9–10 days post-hatch). Whereas dichlorodiphenyldichloroethylene 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 » 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. « less
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Award ID(s):
Publication Date:
Journal Name:
The Biological Bulletin
Page Range or eLocation-ID:
000 to 000
Sponsoring Org:
National Science Foundation
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  2. Abstract

    Most organisms experience thermal variability in their environment; however, our understanding of how organisms cope with this variation is under-developed. For example, in organisms with temperature-dependent sex determination (TSD), an inability to predict sex ratios under fluctuating incubation temperatures in the field hinders predictions of how species with TSD will fare in a changing climate. To better understand how sex determination is affected by thermal variation, we incubated Trachemys scripta eggs using a “heat wave” design, where embryos experienced a male-producing temperature of 25 ± 3°C for the majority of development and varying durations at a female-producing temperature of 29.5 ± 3°C during the window of development when sex is determined. We compared the sex ratios from these incubation conditions with a previous data set that utilized a similar heat wave design, but instead incubated eggs at a male-producing temperature of 27 ± 3°C but utilized the same female-producing temperature of 29.5 ± 3°C. We compared the sex ratio reaction norms produced from these two incubation conditions and found that, despite differences in average temperatures, both conditions produced 50:50 sex ratios after ∼8 days of exposure to female-producing conditions. This emphasizes that sex can be determined in just a few days at female-producing conditions and that sex determinationmore »is relatively unaffected by temperatures outside of this short window. Further, these data demonstrate the reduced accuracy of the constant temperature equivalent model (the leading method of predicting sex ratios) under thermally variable temperatures. Conceptualizing sex determination as the number of days spent incubating at female-producing conditions rather than an aggregate statistic is supported by the mechanistic underpinnings of TSD, helps to improve sex ratio estimation methods, and has important consequences for predicting how species with TSD will fare in a changing climate.

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