Evolutionary and genetic mechanisms of phenotypic plasticity in the Mexican spadefoot toad, Spea multiplicata

Phenotypic plasticity is a fundamental property of life. Plasticity has long been theorized to play a vital role in major ecological and evolutionary processes. However, while the evolutionary consequences of plasticity have been well documented, much less is known about the origins of plasticity itself. In this dissertation, I present key findings about the genetic and transcriptional mechanisms underlying plasticity. Adaptive plasticity consists of two main components: the ability to accurately assess the environment, and the capability to produce a matching phenotype. I performed genome-wide association studies of both environmental assessment and morph production to examine their underlying genetic bases in my second chapter. My results demonstrate that these two components of plasticity have different genetic architecture, as well as providing a set of putative variants underlying phenotypic plasticity. In chapter three, I considered whether novel, complex forms of plasticity arise by co-opting mechanisms from ancestral forms of plasticity. I performed differential gene expression analyses on two forms of plasticity in two species of spadefoot toads, and found that the derived, novel polyphenism primarily arises via lineage-specific changes in gene expression, but a small set of shared differentially expressed genes may provide the substrate for complex polyphenisms to begin to evolve. Finally, in my fourth chapter I present a proposed research program to further investigate the transcriptional mechanisms and morphological processes that shape novel forms of plasticity. In total, this work provides a first attempt at comprehensively characterizing the genetic and transcriptomic origins of phenotypic plasticity, a set of new or improved genomic resources for spadefoot toads, and a roadmap for future investigations into crucial questions about the mechanisms underlying the evolution of plasticity.