MORPHOLOGICAL PLASTICITY AND DIVERGENCE IN LIFE-HISTORY TRAITS BETWEEN TWO CLOSELY RELATED FRESHWATER SNAILS, LYMNAEA OVATA AND LYMNAEA PEREGRA

Abstract

To reveal whether there are genetic differences between two closely related freshwater snails, Lymnaea peregra and L. ovata, which differ in habitat preferences, we studied life-history and morphological variation under laboratory conditions. The status of these taxa as biological species remains under debate, since it is not known to what extent their characteristic shell forms are genetically determined. For each species, we used individuals from two separate origins in experiments to test whether lifehistory variation is more pronounced between populations of different species than between populations of the same species, as would be expected if genetic divergence rather than phenotypic plasticity explains the variation. In addition, we compared shell morphology of wild-caught individuals to individuals maintained in the laboratory for two generations. Our results indicate that when these species are grown under the same conditions, the life-history traits (juvenile growth rate and reproductive schedule) do not converge, supporting the genetic divergence hypothesis. However, the shell of both L. ovata and L. peregra showed considerable morphological plasticity in response to laboratory conditions and converged to a similar form in just two laboratory generations.