Reproductive Life History and Host Fish Selectivity of Imperiled Freshwater Mussels in the Guadalupe River, Texas

Information on mussel reproductive life history, age and growth is important for understanding evolutionary and ecological relationships and predicting how species will respond to threats and various conservation and management strategies. In Texas, located within the southwestern United States, 11 species are pending review for listing under the Endangered Species Act, and information on their reproductive life history and age/ growth is not available. To address this knowledge gap, I examined these aspects for three species (Cyclonaias pustulosa (Pimpleback), Cyclonaias necki (Guadalupe Orb), and Fusconaia mitchelli (False Spike) from a site in the lower Guadalupe River, located in central Texas. The resulting information was then compared with existing life-history information for closely related congeners. I observed peak gamete production in late January and early February for all three species, indicating that spawning occurred during this time. Brooding was observed in all species between March and June, and brooding behavior and glochidia morphology were similar to those of congeners. Accumulated degree days were important in regulating the timing of gametogenesis and potentially the duration of brooding. Fecundity estimates for C. necki and F. mitchelli were much lower than the values reported for congeners and increased with age and length, although length was a better predictor than age. Trematode infestation rates were high (~30%) in C. pustulosa and C. necki, and sex ratios were skewed toward males, indicating that females may be disproportionately affected. The age and growth estimates for C. necki and F. mitchelli closely mirror those of related congeners, although the maximum observed age for C. petrina did not meet theoretical expectations based on the estimated growth (K) rate for this species, indicating reduced longevity. Taken together, my findings suggest that C. petrina and F. mitchelli are experiencing impacts to reproduction that may have negative consequences on long-term population maintenance and persistence for these species in the Guadalupe River. I also conducted laboratory trials that tested host suitability of 12 fish species (4 families, and 11 genera) for C. necki and 8 species (4 families and 7 genera) for F. mitchelli. For C. necki, four host species, Ictalurus punctatus (Channel Catfish), Pylodictus olivarus (Flathead Catfish), Noturus gyrinus (Tadpole Madtom), and Ameirus natalis (Yellow Bullhead) were identified. The transformation period was 11 to 22 days for I. punctatus (peak metamorphosis at 15 days), 16 days for P. olivaris, and A. natalis, and 10 days for N. gyrinus. Two host species, Cyprinella lutrensis (Red Shiner) and Cyprinella venusta (Blacktail Shiner), were identified for F. mitchelli. The transformation period was 18 days for both C. lutrensis and C. venusta. The hosts identified in this study combined with current information on their status within the Guadalupe River indicate that imperilment of C. necki and F. mitchelli may be partially related to the status of their host fish. These results also provided critical information for informing recovery activities such as translocation and captive propagation, if deemed necessary for both species