Phylogeography of lagenorhynchus acutus and lagenorhynchus albirostris and phylogeny of the genus lagenorhynchus

Abstract

This study had two main objectives: to clarify the phylogenetic position of the species cuiTently classified in the genus L igenorhynchus, using a ทานItilocus phylogenetic approach; and to understand the evolutionary history, population structure and phylogeography of L acutus and L. albirostris and the processes that have influenced their distribution in the North Atlantic, using microsatellites and mitochondrial markers.The combined phylogeny analyses performed in this study, using seven nuclear genes and two mitochondrial genes, strongly supports the artificiality of the genus and suggests deep divergences between L. acutus and L albirostris and between these two species and the other members of the genus. Their relationships with members of the subfamily Delphininae were not corroborated, suggesting that these two species possibly deserve to be classified in a new subfamily. The total evidence phylogeny supports previous findings by other authors about the paraphyly of the other four species of the genus Lagenorhynchus, L, obscurus and L, obliquidens are clearly sister taxa, but they do not appear to be closely related to L. australis and L. cruciger, which are more related to Cephalorhynchus lineage; thus this study suggests that these species should probably be assigned to different genera.The time of the most recent common ancestor between L, acutus and L. albirostris was placed during the late Miocene-early Pliocene (〜6.53 MY ago), predating the time of splitting between these two species (〜6Ό^ MY ago). This finding plus the placement of both species at the base of the phylogenetic tree suggest a North Atlantic origin for the ancestor of L. acutus and L. albirostris. In this study, I suggest that the ancestral populations probably migrated toward the North Pacific via the Bering Strait or via the Panamie portal during the Miocene-early Pliocene and that L. obUcjuidens probably diverged and speciated from these ancestral populations.The evolutionary history and population structure of L. acutus and L. albirostris were assessed using a fragment of the control region of the mitochondrial DNA (d loop) of 166 samples for L. acutus and 122 samples for L. albirostris in four geographic areas in the North Atlantic. Both species had moderate haplotypic diversity (0.9170 and 0.7320, respectively) but very low nucleotide diversity (0.0095 and 0.0056, respectively). These findings suggest that populations of both species were affected by historical bottleneck events that reduced their population sizes probably during the Plio-Pleistocene epoch and that their populations are in expansion.When addressing the population division, the Fst values showed a clear differentiation between L. albirostris populations on both sides of the North Atlantic and in the eastern North Atlantic. This study also suggests the existence of one continuous population of L. acutus throughout its geographic range and the presence of one isolated population in the southern North Sea. These results revealed differences in the evolutionary histories of both species, which may be related to preferences in the use of habitat, and dispersion abilities. For example L. acutus is a pelagic species, with preferences for warm temperatures (>12 C) and deep waters, whilst L. alhirosiris is restricted to shallow and coastal areas (<120ทา) and prefers colder waters (<12 C).