Genetic differentiation in the ice-dependent fish Pleuragramma antarctica along the Antarctic Peninsula

Aim: Pleuragramma antarctica is an Antarctic notothenioid fish with a pelagic life-cycle. It plays a major trophic role in coastal Antarctic waters as a predator of krill and as prey for penguins and seals. A previous study, using mtDNA to investigate Pleuragramma population structure at multiple Antarctic sites was unable to discriminate between hypotheses of panmixia, with occasional fluctuations of allelic frequencies, and population structure. The aim of the present study was to investigate the population structure of P. antarctica along the Antarctic Peninsula (AP) shelf by microsatellite genotyping. Location: Four areas along the AP shelf: Charcot Island, Marguerite Bay, Joinville Island and the Larsen Ice Shelf. Methods: A total of 562 individuals from nine population samples were genotyped at 16 expressed sequence tag (EST)-linked microsatellites. Genetic variability, Hardy-Weinberg probabilities and F-statistics were calculated, and a hierarchical analysis of molecular variance was carried out. A Bayesian method was applied to estimate the migration rates between geographical localities. Results: We found one genetically homogeneous population with no interannual variability in the south-western AP and one off the northern tip of the AP. Significant differences were recorded between the two geographical regions, which also differed from the eastern AP. The extent of differentiation changed between years and significant genetic differentiation was found between clusters of individuals of different length modes collected at Joinville Island in 2010. Bayesian analysis suggested weak gene flow along the western AP, with a prevailing direction from north to south, following the anticlockwise-flowing Coastal Current. Main conclusions: Population genetic structure can be detected in AP shelf samples of P. antarctica. Thus, even in this area characterized by strong oceanographic currents, genetic mixing is not complete. Temporal fluctuations of allelic frequencies and genetic differentiation between individuals of different length collected at the same location suggest the importance of genetic drift in this highly abundant species.