ABSTRACT
Previous studies on two common widespread intertidal acorn barnacles, Tetraclita squamosa and Chthamalus malayensis, in the Indo-West Pacific region have identified genetically distinct lineages, representing several cryptic species. In this paper, we summarize the data on COI divergence of the two species complexes to elucidate the geographic distribution and population genetic structure of each lineage, and compare the phylogeographic patterns and timing of speciation events of the species complexes. We found that the genetic differentiation of both complexes is affected by sea level fluctuations associated with glaciations. T. squamosa, however, exhibits a deeper divergence and stronger genetic population structuring which may be attributed to its more stringent habitat requirements (mostly on exposed rocky shores) than C. malayensis (found on shores of varying wave exposures). Within each complex, lineages with a continental distribution appear to suffer more in terms of effective population size from sea level changes than those inhabiting islands. Comparative phylogeographic studies on these barnacles suggest that habitat specificity, rather than larval dispersal capability, appears more important in determining population structure and phylogeographic patterns and highlights the importance of islands in serving as refugia for species during glaciation periods.
