Fundamental aspects of sperm biology for ecologically and economically important bivalve species in Alabama: Cellular signaling, morphology, and density quantification

Abstract

The Eastern oyster, Crassostrea virginica, and freshwater mussels, Ligumia subrostrata and Lampsilis straminea, are significant keystone species in the Eastern United States. These bivalves both provide invaluable environmental enrichment services such as biofiltration and habitat stabilization. Oysters are economically valuable as they are one of the largest contributors to shellfish aquaculture production, while freshwater mussels are of interest due to their ecological contributions and intricate reproductive tactics and life histories. This thesis conducted studies on fundamental aspects of sperm biology for C. virginica, L. subrostrata and L. straminea. Productive water along the coastline of Alabama supports many C. virginica farms, which usually rely on oyster seed provided by hatcheries. High fertilization success can increase oyster aquaculture production, and many aspects of sperm biology are linked to fertilization success, such as sperm motility. Thus, this thesis investigated the physiological aspects regulating sperm motility initiation. Different salinity, pH, and ion activation medias all impacted sperm activity parameters. These findings can be used to enhance fertilization success and assist with development of short-term storage and cryopreservation media. Alabama is a global hotspot for freshwater mussel diversity. Unfortunately, they are in steep decline. Conservation efforts are focusing on propagation techniques to save these imperiled organisms. However, there is limited information regarding seasonal sperm production and morphology, as well as efficient techniques to quantify sperm production regarding freshwater mussels. Thus, this thesis examined sperm densities and morphology across the spawning season of L. subrostrata and L. straminea. Both species displayed an increase and subsequent decrease in sperm concentration over the sampling period as well as an increase in sperm head morphology over time. Tools were also developed using microspectrometery and regressions to accurately estimate sperm concentrations. The seasonal spawning data and microspectrometery techniques can contribute towards propagation efforts and cryopreservation techniques of freshwater mussels.