Variation in fecundity and other reproductive traits in freshwater mussels

1. Life histories of the highly diverse and endangered North American freshwater mussel fauna are poorly known. We investigated reproductive traits of eight riverine mussel species in Alabama and Mississippi, U.S.A.: Amblema plicata, Elliptio arca, Fusconaia cerina, iizmpsilis ornafa, Obliquaria refzexa, Pleurobema decisum, Quadrula asperata and Q. pustulosa, and compare our results with existing life history information for other species. 2. These eight species had reproductive traits characteristic of large, outcrossing populations: hermaphrodites were rare, we found no evidence of protandry, and sex ratios were even or slightly male-biased. 3. Age at sexual maturity varied among species, ranging from cl to 2 years for L. ornata to 3-9 years for Q, asperafa. In all species, most mature females participated in reproduction and fertilisation success was high. 5. Fecundity was related positively to both length and age, but length was the best predictor. In six species, fecundity increased exponentially with increasing size; in two species the rate of increase in fecundity declined in larger animals. In four species, fecundity declined in older animals. These latter results indicate weak reproductive senescence; however, in all species, older individuals continued to produce large numbers of offspring. Mean annual fecundity differed widely among species ranging from 9647 to 325 709. Within-species differences in fecundity were found among rivers and among populations within a river. 6. The wide variation in reproductive traits among species indicates the existence of widely divergent life history strategies in freshwater mussels.