FRESHWATER INVERTEBRATES ON OCEANIC ISLANDS: COLONIZATION, POPULATION STRUCTURE AND SPECIATION.

D.T. Bilton, L.C. Kelly, and S.D. Rundle. Department of Biological Sciences, University of Plymouth, Plymouth, UK PL4 8AA

There is a general paucity of freshwater taxa on most oceanic island archipelagos, this resulting from the dispersal barrier of the sea, and, often, the scarcity of freshwater habitats. Archipelago species pools are typically impoverished and disharmonious, being assembled through chance colonisation of taxa from mainland source pools. The isolation and age of the Canary Islands, situated off NW Africa have resulted in a high degree of endemism in their biota, including freshwater invertebrates. In contrast to many terrestrial groups, however, most endemic aquatic species occur across the archipelago, with single-island endemics almost entirely lacking. This talk presents a summary of recent genetic work on Canarian Trichoptera and Coleoptera, and discusses patterns of dispersal and colonization within and between islands, and the evolution of endemic taxa.