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Abstract
Developmental plasticity, the irreversible modification of phenotypes in response to the developmental environment, carries critical implications for ecology, evolution, and conservation. In some cases, responses to the developmental environment can be beneficial, increasing organismal fitness. However, when developmental environments are altered by human activities, normal developmental trajectories can become disrupted, resulting in negative fitness outcomes. Despite their significance, however, the ecological and evolutionary dynamics of adaptive and disruptive plasticity in natural systems are not well understood. In this dissertation, I utilize unique attributes of the American alligator (Alligator mississippiensis) to integrate developmental plasticity into eco-evolutionary contexts, seeking to connect proximate mechanisms to ultimate outcomes in nature. In Chapter 2, I focus on the disruptive effects of environmental contaminants, testing how maternally deposited hormones and contaminants contribute to gonadal gene expression. I provide novel insight into how reproductive development is altered in contaminated populations and support a non-trivial role of maternally deposited hormones in driving offspring sexual development. Chapters 3-6 center on plasticity in response to incubation temperature and temperature-dependent sex determination (TSD). In Chapter 3, I assess the evolutionary potential for developmental plasticity to drive morphological differences across populations, revealing variable responses to incubation temperature across northern and southern population pairs that are associated with phenotypic divergence. Building off these findings, I then investigate divergence in the molecular pathways associated with TSD across those populations in Chapter 4. My results support unique evolutionary processes acting on TSD genes and highlight several candidate genes for its adaptive evolution. In Chapter 5, I identify time-dependent relationships between incubation temperature, hatchling phenotypes, and post-release traits that contribute to temperature-dependent survival outcomes supported to drive the adaptive evolution of TSD. Finally, in Chapter 6, I evaluate the use of blood gene expression patterns to non-lethally sex hatchling alligators. I demonstrate promising potential for using gene expression to predict natural sex ratios in TSD species, which will aide in incorporating TSD into ecological frameworks and assessing population responses to environmental change. When viewed altogether, my dissertation contributes novel mechanistic, ecological, and evolutionary insights into developmental plasticity as it occurs in nature.