MECHANISMS OF ACCLIMATION AND ADAPTATION IN THE SEA URCHIN ECHINOMETRA SP. EZ

Climate change has resulted in warming of coastal aquatic habitats around the world at almost every latitude, threatening ecosystems with a significant loss in biodiversity and occurring at a rate that may exceed species’ ability to adapt. Understanding how reef species survive in habitats that currently experience extreme temperatures will help identify the biological processes that will govern future responses to climate change. The Persian/Arabian Gulf experiences the warmest coral reef temperatures on the planet (summer maxima ~35-36°C but can exceed 37°C) and connects to the neighboring Gulf of Oman, which experiences more benign environmental conditions (summer maxima of ~30-32°C). Here, we leverage this unique environmental gradient as a natural laboratory to better understand how the keystone sea urchin Echinometra sp. EZ copes with thermal extremes. Species survival in extreme habitats is dependent on their ability to acclimate over the course of an organisms’ lifetime and adapt over the course of many generations. Two complementary mechanisms for coping with environmental change are shifts in the host-associated microbial community, which can happen on a timescale of hours to days, and classic Darwinian evolution in which selection results in different patterns of alleles between populations over many generations. Here, we identify temperature as a robust predictor of community-level microbial variation and highlight specific bacterial taxa that may be crucial for maintenance of host homeostasis during thermal extremes. Next, we show that while there is a high degree of genetic admixture between all sites and bidirectional gene flow between the two seas, there is also significant population differentiation. We describe nine candidate loci that are under putative selection, including one collagen gene. Finally, we sequence, assemble, and annotate a chromosome-level genome that will add substantial value to future functional genomic datasets. Together, the research composing my dissertation has identified the importance of novel microbiome and genomic variation in the adaptation of a dominant ecosystem engineer to the warmest marine environment on Earth. These integrative results provide a foothold for understanding shared and unique mechanisms for the adaptation of marine species to historic and ongoing climate change.