Anthropogenic climate change is challenging wild population to adapt and acclimate at increasingly rapid rates. Keystone marine species, like reef-building corals, are struggling to keep pace and populations are declining at unprecedented rates, threatening important ecosystem functions that coral reefs provide. However, resilient individuals from extreme environments may contribute to the survival of subsequent generations through the transfer of heritable heat tolerance, but human intervention is likely required to harness this adaptive potential to content with current warming trends. There is therefore an essential need to understand how to leverage these resilient individuals to enhance the adaptive capacity of these keystone species.
In 2019, the French Polynesian island of Mo’orea experienced a severe mass bleaching event accompanied by widespread coral mortality. At the most heavily impacted sites, we observed Acropora hyacinthus individuals that were resistant to bleaching, alongside colonies that bleached but showed signs of symbiont recovery shortly after the bleaching event. Using these colonies as a natural experiment, we are assessing energetic and reproductive consequences of these different responses to heat stress. Further, we are examining the potential for symbiont communities, host genotype and epigenetics to have contributed to survival and recovery of extreme stress event. This work will be important for understanding mechanisms of resiliency in Moorea’s coral reefs.
While many ecologically important marine species are facing considerable declines in the face of anthropogenic change, some species are highly robust to human disturbed environments and are increasing in abundance worldwide. One example is the upside-down jellyfish in the genus Cassiopia, which is becoming increasingly common in tropical coastal habitats. These jellyfish show immense resilience to high temperatures, light intensity, and salinity but there is little known about the role of phenotypic plasticity plays in their ecological success. We are developing Cassiopeia as a model to study outstanding questions about phenotypic plasticity in the face of global change.
Using the purple sea urchin (Strongylocentrotus purpuratus), we have found that the timing of exposure to different environmental conditions influences epigenetic responses: parental conditioning during gametogenesis induces significant changes in DNA methylation of the offspring. However, we observed little connection between changes in DNA methylation to changes in gene expression (Strader et al. 2019, 2020). Following up on this, differential gene expression was modeled as a function of DNA methylation across genomic features and chromatin states (Bogan, Strader and Hofmann, in review). Through this, we found a positive correlation between differential intron methylation and gene expression, an effect that was strongest amongst lowly expressed genes with accessible transcription start sites. Therefore, we have found that changes in epigenetic patterns induced by environmental change likely have multiple, context dependent, functional roles during organismal response to the environment.
To investigate this further, we are examining the role of epigenetic modification on the development of the immune response in S. purpuratus. We are modulating different microbial and temperature environments throughout the life-cycle to link epigenetic changes that occur in response to shifting environments to organismal phenotypes with an emphasis on immune function. The proposed work is designed to answer the following three questions: 1) To what extent is the epigenomic landscape inherited via the germline? 2) How does the environment experienced during embryogenesis shape the epigenome? 3) How does the environment experienced during embryogenesis shape the larval immune response? Utilizing the larval stage of the purple sea urchin, which is an experimentally tractable and ecologically relevant model system gives us an ideal system to address gaps of knowledge connecting the environment, the epigenome and immune phenotypes.
Purple sea urchins are widely distributed across the Pacific coast of the United States and experience highly dynamic environmental fluctuations associated with upwelling. With large population sizes and little population structure across the range, this species is ideal for examining the relative roles of adaptation and phenotypic plasticity in response to differences in abiotic environmental conditions. By generating individual level crosses between purple sea urchins conditioned to variable environments we have teased apart the extent of parental and developmental effects on phenotypic plasticity as well quantified additive genetic variance and evolvability (Strader et al. in review).
