CONSERVATION GENETICS OF NORTH-AMERICAN FRESH-WATER MUSSELS AMBLEMA AND MEGALONAIAS

Freshwater bivalves are among the most endangered groups of organisms in North America. Efforts to protect the declining mussel fauna are co nfounded by ambiguities associated with recognition of distinct evolut ionary entities or species. This, in part, is due to the paucity of re liable morphological characters for differentiating taxa. We have empl oyed allozymes and DNA sequence data to search for diagnosably distinc t evolutionary entities within two problematic genera of unionid musse ls, Amblema and Megalonaias. Within the genus Amblema three species ar e recognized based on our DNA sequence data for themitochondrial 16S r RNA and allozyme data (Amblema neislerii, A. plicata, and A. elliotti) . Only one taxonomically distinct entity is recognized within the genu s Megalonaias-M. nervosa. Megalonaias boykiniana of the Apalachicolan Region is not diagnosable and does not warrant specific taxonomic stat us. Interestingly, Megalonaias from wet of the Mississippi River, incl uding the Mississippi, exhibited an allozyme and mtDNA haplotype frequ ency shift suggestive of an east-west dichotomy. The results of this s tudy eliminate one subspecies of Amblema and increase the range of A. plicata. This should not affect the conservation status of ''currently stable'' assigned to A. plicata by Williams et at. (1993). The conser vation status of A. elliotti needs to be reexamined because its distri bution appears to be limited to the Coosa River System in Alabama and Georgia.