Reproductive Biology and Host Requirement Differences Among Isolated Populations of Cyprogenia Aberti

Cyprogenia aberti, the Western fanshell, is a rare and threatened pearly mussel endemic to the Interior Highlands of Eastern North America. Previous genetic analysis suggested that multiple species are present within this taxon. The present study sought phenotypic differences among genetically distinct populations in the upper Arkansas River system (Verdigris and Spring rivers), the St. Francis River, and the Ouachita River. Like other native mussels, the glochidia larvae of Cyprogenia are obligate parasites on particular species of host fish. Transformation success of glochidia was compared among 8 species of Percina and Etheostoma. The percentage of attached glochidia that transformed on individual fish ranged between 0 and 86%. Effective hosts (those that transformed a large proportion of attached glochidia) were always sympatric with the mussel population, and species with narrow geographic range were effective hosts only for sympatric mussel populations. However, two populations of a geographically widespread host species, the logperch, were effective host for each mussel population tested. The timing of glochidia and juvenile drop-off appeared to be relatede to the age or maturity of the glochidia. Glochidia size and shape differed among mussel populations. Conglutinate color, which is determined by the color of undeveloped eggs, varied within and among populations. Upper Arkansas mussels produced only white conglutinates. Ouachita and St. Francis mussls produced either red or brown conglutinates. The conglutinate color of individuals in the Ouachita and St. Francis populations correlated with two widely diffrent mitochondrial genotypes present in both of these populations. Overall, the results demonstrate that all three mussel populations are distinct and they should be recognized and protected as such