Population structure and long-term decline in three species of heart urchins Abatus spp. near-shore in the Vestfold Hills region, East Antarctica

Abstract

Patterns of fine-scale spatial population structure in Antarctic benthic species are poorly understood. There is a high proportion of brooding species in the Antarctic benthos, and a brooding life history strategy is expected to restrict their dispersal abilities and therefore foster population structure. Additionally, genetic structuring of populations can preserve signals of historic processes (such as Pleistocene glaciations) on species distributions and abundances. We developed a set of 7 microsatellite markers to examine population genetic variation and infer the demographic history of 3 sympatric Antarctic sea urchin species from the order Spatangoida (Abatus ingens, A. shackletoni and A. philippii), all with brooding life history strategies. Samples were collected at 5 sites separated by up to 5 km, in the near-shore area surrounding Davis Station in the Vestfold Hills area of the Australian Antarctic Territory. We found evidence of a long-term population decline in all 3 species, and the estimated timing of the decline precedes anthropogenic activities and is compatible with long-term climate variability. Two genetic clusters in A. ingens and A. shackletoni suggest secondary contact after population differentiation in glacial refugia. Life history is not a good predictor of fine-scale population structure in these species, with gene flow possible at distances of 5 km. Finally, no evidence was found for a potential impact of pollution from Davis Station on genetic variation. The reduced effective population size observed for these Antarctic benthic species highlights their fragility and the need for conservation concern.