Speciation in the dark: diversification and biogeography of the deep-sea gastropod genus Scaphander in the Atlantic Ocean.

The prevailing mode of speciation in Scaphander was allopatric, but one possible case of sympatric speciation was detected between two western Atlantic species. Sister relationships between IWP and Atlantic lineages suggest the occurrence both of vicariance events caused by the closure of the Tethyan Seaway and of dispersal between the two ocean basins, probably around South Africa during episodic disruptions of the deep-sea regional current system caused by glacial-interglacial cycles. Cladogenetic estimates do not support comparatively older diversification of deep-sea faunas, but corroborate the hypothesis of a pulse of diversification centred in the Oligocene and Miocene epochs. Amphi-Atlantic species were found to occur at deeper depths (bathyal-abyssal) and we hypothesize that trans-Atlantic connectivity is maintained by dispersal between neighbouring reproductive populations inhabiting the abyssal sea floor and by dispersal across the shelf and slope of Arctic and sub-Arctic regions.