Genetic connectivity of Trematomus fishes in the Southern Ocean

Polar ecosystems harbour a unique cold-adapted biodiversity that is threatened by rapid environmental change and increasing anthropogenic impact. In this context, collecting data on connectivity between populations is essential for supporting conservation management of living resources and ecosystems. Genetic connectivity is the extent to which populations in different parts of a species' geographical range are linked by the exchange of larvae, juveniles or adults (which are the vectors of genetic material). In the Southern Ocean, several Marine Protected Areas (MPAs) – large areas where human activities are restricted or prohibited to promote conservation – are established or under negotiations. Such MPAs are most effective if implemented as a network that considers genetic diversity and connectivity within and between species. In the present study, 607 individuals of ten Trematomus species were sequenced using reduced representation sequencing techniques. Thousands of genomic variants were used to investigate inter- and intraspecific patterns of divergence and connectivity across the Southern Ocean shelf. Population structure analyses of four different species (T. loennbergii, T. eulepidotus, T. scotti and T. newnesi) suggest long- range dispersal across the Weddell Sea and even along the entire West Antarctic coast that might be facilitated by the Weddell Sea Gyre and Antarctic Coastal current. A genetic break at the level of the Filchner Trough was observed in several species. The strong outflow from the Filchner-Ronne ice shelf may separate the trough area from the remaining Weddell Sea habitat. Finally, results suggest that previously undetected cryptic species may be present within both T. eulepidotus and T. loennbergii. Altogether, the present results contribute to the assessment of diversity and connectivity on the Southern Ocean shelf, which is imperative in view of unprecedented global change.

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