Discordant patterns of morphological and genetic divergence in the 'Austrocochlea constricta' (Gastropoda: Trochidae) species complex

Abstract

Patterns of genetic and morphological divergence were examined among Western Australian (Abrolhos Islands and Albany) and Tasmanian members of the highly variable 'Austrocochlea constricta' species complex. Analyses of allele frequencies at 13 enzyme loci confirmed the presence of three species within this complex in Tasmania, revealing additional diagnostic differences not previously detected. Where combinations of species sympatry were examined in Tasmania, seven diagnostic loci separated A. constricta and A. brevis, four separated A. porcata and A. brevis, and one separated A. porcata and A. constricta. Western Australian animals were genetically most similar to Tasmanian A. constricta populations, separated from them by genetic distances of just 0.018 (Albany) to 0.107 (Abrolhos), despite spatial isolation over ~3000 km. These genetic distances, in addition to that separating Abrolhos and Albany populations (0.138), are considered within the range possible for allopatric conspecifics. In comparison, genetic distances separating A. constricta from sympatric A. porcata (0.191) and A. brevis (0.803) in Tasmania were much larger. However, on the basis of a range of morphological traits, which were species-diagnostic in Tasmania, Abrolhos animals most closely resembled A. porcata, and Albany animals appeared intermediate to A. porcata and A. constricta. This suggests Australia-wide discordance among genetic and morphological characters of the 'A. constricta' complex.