GENETIC SUBDIVISION OF THE INTERTIDAL SNAIL BEMBICIUM-VITTATUM (GASTROPODA, LITTORINIDAE) VARIES WITH HABITAT IN THE HOUTMAN ABROLHOS ISLANDS, WESTERN-AUSTRALIA

The littorine gastropod Bembicium vittatum has benthic egg masses and is thought to have little or no period of planktonic development. A study of allozyme polymorphisms in populations from the Houtman Abrolhos Islands, Western Australia, permitted examination of genetic subdivision within and among island groups, and among populations from contrasting habitats which occur throughout the Abrolhos archipelago. Across all populations, the average F(ST) for five polymorphic loci was 0.163, which is very large for a marine species but similar to values found for other gastropods that lack planktonic development. The level of genetic subdivision varied dramatically with habitat. Over similar distances, the average F(ST) among lake populations was 0.277, compared with 0.138 among populations from protected lagoonal shores, and only 0.022 among populations from relatively exposed shores. This variation emphasizes the need to consider local conditions when attempting to determine the genetic structure of a species.