Speciation in brooding and poorly dispersing lacustrine organisms

Studies of interpopulation variability in brooding and nonbrooding taxa from Lake Tanganyikan ostracodes support the hypothesis that gene flow between populations of lacustrine brooders may be greatly inhibited by extreme localization of gene pools. Significant interpopulation variability occurs among populations of the brooding Mesocythere irsacae in the absence of habitat barriers, whereas sympatric nonbrooding populations of a cytherideid ostracode, n. gen., n. sp. A. show minimal variation over the same range. Extreme genetic isolation may cause rapid speciation and extinction in such populations, owing to the vagaries of small population sizes. When a lake persists for geologically long periods of time selective pressures for excellent dispersal mechanisms may relax. Under such circumstances, clades of lacustrine brooding organisms, which are often poor dispersers, would radiate and suffer extinctions at accelerated rates. -from Authors