The American horseshoe crab Limulus polyphemus has a species range extending from Maine to Florida, along the gulf of Mexico and the Yucatan Peninsula of Mexico. Along its range exists genetically distinct and geographically isolated populations. Adult horseshoe crabs nest on sandy beaches during biweekly spring tides depositing nests of fertilized eggs within the sand. The developing embryos are exposed to multiple environmental stressors (heat, hypo-salinity, hypoxia, hydrogen sulfide) during their 2-week incubation, and developing in time for the following high tide is essential for larval survival. My research has shown that adult horseshoe crabs nest along beach locations that maximize embryo development and that exposure to multiple environmental stressors can result in synergistic and antagonistic interactions that can influence development success. Lastly, by comparing multi-stressor responses between 2 distinct populations (Florida Gulf Coast and Delaware Bay), I have shown that microclimate stressor exposure can influence stressor tolerance more so than latitudinal location.
Horseshoe crabs nesting at Seahorse Key, FL.
Marine intertidal mussels are exposed to daily tidal fluctuations influencing environmental stressor exposure. Aerial emersion at low tide can result in physiological hypoxia, heat exposure, dessication and predation. Mussels of the genus Mytilus are dominant along the Pacific Coast of the US. Mytilus galloprovincialis, which is heat tolerant but vulnerable to hypo-salinity, invaded southern California and has become dominant out-competing the native M. trossulus. M. trossulus is hypo-salinity tolerant but vulnerable to heat and can now only be found north of San Francisco Bay. The differences in stressor tolerance between the two species make them ideal organisms for studying stressor tolerances. My work has used comparative proteomics to analyze differences in protein abundance changes in these two organisms in response to: 1) aerial emersion hypoxia, 2) aerial heat and hypo-salinity, and 3) sirtuin inhibition. Sirtuins, which are NAD-dependent deacetylases, are known to regulate key cellular stress components in model organisms, but have never been tested in marine invertebrates. By using sirtuin inhibitors, I have been able to investigate the regulation of the cellular stress response by sirtuins in Mytilus. My research has shown that proteins involved in antioxidant responses to oxidative stress (Cu/Zn-SOD, peroxiredoxin, thioredoxin), energy metabolism (NADP isocitrate dehydrogenase), molecular chaperones (HSP70, sHSPs), and cell signaling (MEK/ERK) are significantly decreased under sirtuin inhibition and various stressors tested, thereby highlighting sirtuins' role in stress tolerance in Mytilid mussels.
M. galloprovincialis and M. trossulus mussels being exposed to multiple stressor conditions in tidal simulators (Cal Poly San Luis Obispo, CA).