Doctor of Philosophy (PhD)
Climate change and other anthropogenic impacts are causing rapid alterations to many of the world’s most productive coastal ecosystems and there is an urgent need to understand how species will respond to these environmental changes. Organisms may respond through plasticity, evolution, or the evolution of plasticity. In this dissertation, I evaluate the role of plastic and evolved responses in the eastern oyster, Crassostrea virginica, to environmental variation in the northern Gulf of Mexico. I use comparative transcriptomics, physiology, and morphology to examine the relative contribution of plastic and evolved responses for oysters exposed to low salinity and outplant sites naturally differing in salinity regimes and levels of the parasite, Perkinsus marinus. Additionally, to further explore evolved responses, I use comparative genomics to obtain a holistic view of the population divergence and evolutionary processes affecting C. virginica in this region. I showed that the relative contribution of plastic and evolved responses depended on the stressor and phenotypic trait measured. Morphological and physiological traits consistently showed a largely plastic response to low salinity and changes in outplant site, but gene expression was shaped either by genotype or environment, depending on the type of stress exposure. Furthermore, I find no evidence either for genetic variation in plasticity or locally adapted traits in response to environmental variation. Overall, this suggests that C. virginica is likely to have a generalized plastic response to environmental change rather than a population-specific response, and that aquaculture or restoration management may not benefit from prioritizing oysters from any specific estuary when focused on a low salinity site. However, population structure analyses support the hypothesis that C. virginica is locally adapted to high salinity in southern Texas, which suggests that aquaculture and restoration management may benefit from using one of the southern populations for growing or restoring oysters at hypersaline estuaries. In my dissertation, I have contributed to the field by providing a useful framework for partitioning the effects of genotype, environment, and genotype-by-environment interactions using morphological, physiological, transcriptomic, and genomic data to quantify the relative contributions of plasticity and genetic variation within a species.
Sirovy, Kyle, "Plastic and Evolved Responses in the Eastern Oyster, Crassostrea virginica, to Environmental Variation in the Northern Gulf of Mexico" (2022). LSU Doctoral Dissertations. 5890.
Kelly, Morgan W.
Available for download on Saturday, June 28, 2025