Spatial pattern of genetic and morphological diversity in the direct developer Acanthina monodon (Gastropoda: Mollusca)

Three biogeographic areas have been recognized along the Chilean coast, with biogeographic breaks located at 30 and 42 degrees S allowing us to test the concordance between biogeographic patterns and spatial patterns of genetic and morphological diversity in marine species. We examined the marine gastropod Acanthina monodon, whose range spans the 2 major biogeographic breaks detected in the South-Eastern Pacific (SEP) coast. This species exhibits high variability in the morphology of its shell and has a direct development cycle. Based on the analysis of mitochondrial sequences of 258 individuals from 9 locations in the 3 biogeographic areas, we found 3 clades with contrasting levels of genetic diversity and with spatial population genetic structure. A perfect match between biogeography and pylogeography was observed only at the 30 degrees S break. In contrast, we did not find a clear genetic break in concordance with the 42 degrees S phylogeographic break, although haplotype distribution suggested a second phylogeographic boundary located between 45 and 53 degrees S. Only one haplotype was observed in the most southerly location, which may be explained by the historical influence of glaciations. A break in shell morphology was evidenced only at around 40 to 46 degrees S, with a group characterized by thinner shells and longer spires compared to the northern group. Our results supported the concordance hypothesis and indicated that the influence of life cycle strategy, habitat discontinuity and historical processes may determine the phylogeographical and shell morphology spatial pattern of A. monodon. In contrast to previous studies, our genetic analysis showed the presence of a single Acanthina species along the SEP coast.