Meeting Abstract
The eastern oyster, Crassostrea virginica, is known for its tolerance of a wide range of salinities, but evidence suggests that some populations may be adapted to their local salinity regime. Distance from the Mississippi River is correlated with increased salinities and oysters are expected to have a decreased tolerance to low salinity as distance from the Mississippi River increases. Larval survival is strongly influenced by the salinity conditions of the parental stock, suggesting that larvae from their ‘home’ or ‘parental’ salinity regime have higher survival than in a ‘foreign’ environment with a different salinity. Oysters have high levels of gene flow which could impede local adaptation, but strong selective gradients may cause differential survival of native and foreign oyster recruits, leading to population structure and adaptation to local salinity regimes. To test for evidence of local adaptation by differential larval survival we imposed a low salinity (7 ppt) selection event on oyster larvae from Louisiana (low salinity environment) and Texas (high salinity environment) populations. A subsample of larvae was collected before and after a 12-hour low-salinity exposure for genetic analyses. “Live” oysters were collected from the top 900mL of the jar and “dead” oysters were collected from the bottom 100mL of the jar. We observed 99% mortality in larvae from the high salinity Texas population and only 70% mortality in larvae from the low salinity Louisiana population, suggesting population-specific survival rates. Using exome capture, we sequenced 150 salinity-associated genes and observed allele frequency shifts in survivors before and after low salinity exposure. These genes are potential candidates under low salinity selection that maintain population structure in C. virginica in the Gulf of Mexico.
