MICROGEOGRAPHIC, GENETIC AND MORPHOLOGICAL-DIFFERENTIATION OF FRESH-WATER SNAILS - THE HYDROBIIDAE OF WILSON PROMONTORY, VICTORIA, SOUTH-EASTERN AUSTRALIA

Population differentiation and speciation in freshwater snails in a sm all geographic area were investigated in a study of the morphology and genetics of 75 populations of hydrobiid snails from streams on Wilson s Promontory, Victoria, Australia. At least four genetically definable species occur in sympatry. One (Fluvidona recta sp. nov.) is genetica lly isolated from the others and the other three (of which only F: tur bata sp. nov. is named) appear to be closely related and distinguished by a nearly fixed allozyme (MPI) difference. Heterozygote frequencies for the diagnostic Mpi locus fall well below Hardy-Weinberg expectati ons in zones of sympatry. There is significant population subdivision within at least two of the genetic species, but as the partitions are allopatric they are not categorised taxonomically. The situation may b e explained by the divergence of upland and lowland populations when s ea levels fell during the Pleistocene with subsequent secondary contac t and low levels of hybridisation in the contact zones. Generally, the re is very low gene flow between even closely adjacent populations and extremely low flow between different catchments, F-ST between populat ions within the same tributary ranging from 0.02 to 0.14 and within ad jacent tributaries of the same catchment ranging from 0.03 to 0.59. So me correlations between allozyme data and measured environmental varia bles were observed but none of these were consistent over all taxa. Si ze (shell length) appears to be influenced by environment, but shell s hape and the length of the opercular smear are more correlated with ge netic patterns. A notable lack of correlation between anatomy and gene tic groupings was found, although there was some with shell and opercu lar morphology. Two additional species (F: gippslandica, sp. nov. and F: foris, sp. nov.) from areas adjacent to the Promontory are used as outgroups.