Antarctic fish Gobionotothen gibberifrons

The diversification of the teleost suborder Notothenioidei (Perciformes) in Antarctic
waters provides one of the most striking examples of a marine adaptive radiation. Along
with a number of adaptations to the cold environment, such as the evolution of antifreeze
glycoproteins, notothenioids diversified into eight families and at least 130 species. Here,
we investigate the genetic population structure of the humped rockcod (Gobionotothen
gibberifrons), a benthic notothenioid fish. Six populations were sampled at different
locations around the Scotia Sea, comprising a large part of the species’ distribution range
(N = 165). Our analyses based on mitochondrial DNA sequence data (352 bp) and eight
microsatellite markers reveal a lack of genetic structuring over large geographic distances
(¦ST £ 0.058, FST £ 0.005, P values nonsignificant). In order to test whether this was due to
passive larval dispersal, we used GPS-tracked drifter trajectories, which approximate
movement of passive surface particles with ocean currents. The drifter data indicate that the
Antarctic Circumpolar Current (ACC) connects the sampling locations in one direction only
(west–east), and that passive transport is possible within the 4-month larval period of
G. gibberifrons. Indeed, when applying the isolation-with-migration model in IMA, strong
unidirectional west-east migration rates are detected in the humped rockcod. This leads us
to conclude that, in G. gibberifrons, genetic differentiation is prevented by gene flow via
larval dispersal with the ACC.
Keywords: adaptive radiation, population genetics, isolation-with-migration model, drifters