LIFE HISTORY PATTERNS OF MERCENARIA MERCENARIA, M. CAMPECHIENSIS, AND THEIR NATURAL HYBRID FORM: DOES GENOTYPE MATTER?

Mercenaria spp. are economically and ecologically important bivalves and commonly found in fossil and archaeological deposits. They have been studied throughout their biogeographic range, and their shells have been used to reconstruct temporal and spatial changes in environmental conditions. Two species of modern Mercenaria occur along the US Mid Atlantic and Gulf Coastal Plains: M. mercenaria (northern quahog) and M. campechiensis (southern quahog). They co-occur in low-latitude, nearshore habitats up to Cape Hatteras, NC. North of Cape Hatteras, M. campechiensis typically occurs farther offshore than M. mercenaria. Physical characteristics such as purple nacre, ridges, and lunule morphology have been used to distinguish between the two species. Because the two species can hybridize, physical characteristics alone are not always diagnostic of genotype, requiring genetic analysis. Identifying genotype in fossil and archaeological populations can be even more uncertain as genetic analysis is not possible. Such uncertainty can potentially have important implications on life history studies of fossil and archaeological Mercenaria shells. This study tests the hypothesis that modern M. mercenaria and M. campechiensis from the same location will have similar life history patterns. The genotype of live-collected specimens from Wilmington, NC (n = 40) and Pineland, FL (n = 9) will be identified using electrophoresis. We will supplement the Florida population with live-collected specimens of both species from nearby Sanibel-Captiva Island provided by the Florida Museum of Natural History (n = 10 for each species). Growth rate and lifespan will be analyzed using the von Bertalannfy growth equation. We will use the mixed model ANOVA (analysis of variance) to test our null hypothesis. Results will allow us to validate the assumption that species-level identification between M. mercenaria and M. campechiensis from fossil and archaeological deposits for life history studies is not required.