Chromosomal Evidence for Parallel Evolution of Shell Sculpture Pattern in Goniobasis

Abstract

Karyotypic variation is described in 2 recognized species of Florida [USA] Goniobasis. G. floridensis has a different karyotype in each of the 3 river basins where it was studied. In 2 adjacent streams, each of which drain a portion of a different river basin, the range of G. floridensis overlaps with that of a smooth-shelled form, G. dickinsoni. The karyotypes of G. dickinsoni within each of these streams is indistinguishable from that of the G. floridensis found there. These 2 stream populations of G. dickinsoni have independently evolved from karyotypically different stocks of Goniobasis and represent parallel evolution of the absence of pronounced shell sculpture.