An approach using ddRADseq and machine learning for understanding geographic and bathymetric patterns of speciation in Antarctic gastropods (Mollusca)

Sampling impediments and paucity of suitable material for molecular analyses have precluded the study of speciation and radiation of deep-sea species in Antarctic ecosystems. Elucidating the factors driving diversification is of profound importance if we want to understand how deep-sea taxa have originated and evolved and may serve to establish the framework for evaluating future anthropogenic alterations, particularly in a highly susceptible region like Antarctica. Here, we analyze genome-wide single nucleotide polymorphisms (SNPs) obtained from double digestion restriction site-associated DNA sequencing (ddRADseq) for most species of antarctophilinid gastropods known to date throughout their geographic distribution and bathymetric ranges. In light of the new data provided for all described and undescribed species identified here, we discuss relevant diversification processes and biogeographic and bathymetric affinities. Novel approaches in species delimitation tests, including unsupervised machine learning methods, are further used to establish species hypotheses frameworks aided by available morphological data. In this sense, several new species are here identified, suggesting allopatric speciation connected to geographic or bathymetric isolation. Higher endemism and higher diversity were found in shallow waters around the Scotia Arc and on the continental shelf in the Weddell Sea. In contrast, the deep sea presents fewer species expanding over great areas in the South-Atlantic Antarctic Ridge, and with a lower incidence of endemism. Our study exemplifies how diachronic paleoclimatic and current environmental factors shaped Antarctic communities both at the shallow and deep-sea levels, promoting Antarctica as a center of origin for numerous deep-sea taxa such as gastropod mollusks.