Abstract
The climate history of the Antarctic continental shelf has formed a diverse benthic ecosystem over evolutionary time scales. The extent of faunal diversity has only recently been unveiled especially by using genetic data. In addition to newly reported species, known species of benthic invertebrates in the Southern Ocean turned out to be in fact species complexes representing genetically very distinct clades. Previous studies have shown that the sea spider Pallenopsis patagonica is such a species complex consisting of several mitochondrial clades. However, genetic analyses of another sea spider complex, Colossendeis megalonyx, showed that looking at one gene only can lead to overestimation of species number within a species complex. In this study we expand the current data set of P. patagonica by adding not only samples from Patagonia, the Subantarctic and the Eastern Weddell Sea, but also sequence data of the nuclear internal transcribed spacer region to obtain more information about the species complex. In fact, the number of clades is reduced when looking at nuclear data, but there are no cases of mito-nuclear discordance and hence no evidence for hybridization and speciation reversal events between divergent mitochondrial clades as has been reported for C. megalonyx. As patterns of genetic differences within P. patagonica and C. megalonyx are very similar when looking at the mitochondrial COI gene and also molecular dating of both species complexes suggest a recent separation of clades during the Pleistocene, different biological processes seem to have led to fast and stable species boundaries in P. patagonica as opposed to C. megalonyx where hybridization even across major mitochondrial lineages was still possible.
Highlights
Increased sampling of Southern Ocean habitats and the application of molecular taxonomy uncovered that Antarctic biodiversity has been drastically underestimated (Gutt et al, 2004; De Broyer and Danis, 2011; De Broyer et al, 2014)
P. yepayekae represented a monophyletic group within P. patagonica s.l
Analysis of the Bayesian tree with Bayesian Poisson Tree Processes (bPTP), suggested the presence of 20 distinct groups, subdivided five ABGD groupings further resulting in seven additional clades
Summary
Increased sampling of Southern Ocean habitats and the application of molecular taxonomy uncovered that Antarctic biodiversity has been drastically underestimated (Gutt et al, 2004; De Broyer and Danis, 2011; De Broyer et al, 2014). Paradoxically the Southern Ocean has emerged from being regarded as a biodiversity sink to a center of marine biodiversity in the past two decades. This phenomenon of high in situ species diversity has been termed the Antarctic diversity pump (sensu Clarke and Crame, 1989). Several processes have been discussed as drivers fueling this diversity pump (Clarke and Crame, 1989) In this context, molecular data have led to a paradigm shift: Most of the cryptic species have rendered the distribution ranges of formerly described species from broad (i.e., circum-Antarctic) to small and allopatric (Lörz et al, 2009; Held, 2014). Prominent signatures of population bottlenecks, in particular for shallow-water organisms, have supported that view (e.g., Janko et al, 2007; Raupach et al, 2010)
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