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Abstract
Seascape genomics is an exciting emergent field that attempts to relate geographic and ecological features to evolutionary patterns that act on natural populations. In the past decade, next-generation sequencing analyses have yielded fascinating insights into non-model marine organisms, from broad-scale demographic history, population connectivity, and local adaptation to an organism’s unique transcriptional response to environmental stressors. Yet these efforts have been disproportionately concentrated on commercially important species, and species of ecological value remain understudied within the framework of seascape genomics. The keystone predator Pisaster ochraceus (ochre sea star) once dominated rocky intertidal ecosystems, but populations are increasingly threatened by a suite of compounding modern stressors. In my first study, I explored the underlying genomic architecture and adaptive differentiation of this species through whole genome (re)sequencing (WGS) on ochre star genomes collected from 10 populations throughout the species’ expansive range (Alaska to Baja California). I uncovered novel signatures of substantial population divergence between ochre stars residing in the sheltered bay of the Salish Sea versus those collected from open coastal sites. This work has considerable implications that extend beyond the fields of genetics/genomics, compelling a reassessment of the fundamental aspects of P. ochraceus and underscoring the intricacies of this species' biology, calling for a more nuanced and regional approach to their study and conservation. In my second study, I leveraged an experiment that induced wasting in ochre sea stars through organic matter amendment in a controlled laboratory setting through a TagSeq-based differential gene expression (DGE) analysis. Among the most compelling results was the identification of an overall wasting ‘arc’ or trajectory composed of individual stars tracing a shared transcriptional response to wasting characterized by 152 significantly DEGs. Another set of 73 DGEs provides compelling evidence for innate physiological differences among orange and purple morphs of P. ochraceus that influence their susceptibility to SSW. Finally, I explored expression trends among individual genes of interest that ultimately support previous reports that SSW symptoms reflect a systemic response to context-dependent stressors, one that is influenced by hypoxic conditions facilitated by microorganisms inhabiting the animal-water interface.