More evidence of speciation and dispersal across the Antarctic Polar Front through molecular systematics of Southern Ocean Limatula (Bivalvia: Limidae)

The previously unclear taxonomic status of the high-Antarctic bivalve Limatula ovalis Thiele, 1912 and the sub-Antarctic L. pygmaea (Philippi, 1845) was investigated using molecular techniques (18S rDNA, 16S rDNA, ITS-1). L. ovalis and L. pygmaea were recovered as sister taxa, and L. hodgsoni (Smith, 1907) as their sister, supporting the subgenus Antarctolima Habe, 1977. Various different molecular clock calculations placed the timing of the L. ovalis/pygmaea divergence (1.36-8.03 MYA with 16S rDNA, 6.81-19.12 MYA with 18S rDNA, 0.24-2.87 MYA with ITS-1) well after the formation of the Antarctic Polar Front (23.5 MYA, APF), indicating a more recent speciation process. The vicariance hypothesis that the APF is a barrier for geneflow favouring speciation processes in the Southern Ocean has to be questioned.