A grant has been awarded to Dr. Walter R. Hoeh at Kent State University to study the molecular systematics and mitochondrial DNA (mtDNA) inheritance in the freshwater mussel (bivalve) tribe Lampsilini. Doubly-uniparental inheritance of mtDNA has been found in marine and freshwater mussels. This system has been studied extensively in marine mussels but relatively little work has been done on the species-rich freshwater fauna. Studies of the doubly-uniparental inheritance system indicate that mtDNA gender-switching events are common in marine mussels; however, recent work suggests that these gender-switching events are absent in freshwater mussels. This situation may be related to a 600 nucleotide extension of the COII gene in freshwater mussel male-transmitted mtDNA. Using DNA sequencing techniques, this project will examine the evolution of the COII extension in the Lampsilini, a group of freshwater mussels that are of particular interest because it contains some of the most interesting morphological adaptations within bivalves as well as a secondary reduction of the COII extension in a species within this tribe. This project's specific objectives include: (1) construct robust estimates of lampsiline phylogeny, (2) investigate the evolutionary pattern of reduction of the COII extension, and (3) examine the molecular evolution of the male- and female-transmitted mtDNAs. These objectives will facilitate tests of lampsiline evolutionary relationships, determine the lability of the COII extension, determine the extent to which the COII extension prevents gender-switching, and increase our understanding of the forces underlying molecular evolutionary change.
The completion of these specific objectives has broad implications, including: conservation of freshwater mussels, one of the most imperiled faunas in the world; the evolution of doubly-uniparental and standard maternal mtDNA inheritance; evolution of morphological sexual dimorphism in the Lampsilini; and mechanisms underlying molecular evolution. In addition, the proposed research will provide training for a young evolutionist/systematist.