Abstract
Dispersal via pelagic larval stages plays a key role in population connectivity of many marine species. The degree of connectivity is often correlated with the time that larvae spend in the water column. The Antarctic notothenioid fishes develop through an unusually long pelagic larval phase often exceeding 1 year. Notothenioids thus represent a prime model system for studying the influence of prolonged larval phases on population structure in otherwise demersal species. Here, we compare the population genetic structure and demographic history of two sub‐ A ntarctic crocodile icefish species ( C haenocephalus aceratus and C hampsocephalus gunnari ) from the S cotia A rc and B ouvet I sland in the A tlantic sector of the S outhern O cean to delineate the relative importance of species‐specific, oceanographic and paleoclimatic factors to gene flow. Based on 7 ( C . aceratus ) and 8 ( C . gunnari ) microsatellites, as well as two mitochondrial DNA markers (cytochrome b , D ‐loop), we detect pronounced population genetic structure in both species ( amova FST s range from 0.04 to 0.53). High genetic similarities were found concordantly in the populations sampled at the S outhern S cotia A rc between E lephant I sland and S outh O rkney I slands, whereas the populations from B ouvet I sland, which is located far to the east of the S cotia A rc, are substantially differentiated from those of the S cotia A rc region. Nonetheless, haplotype genealogies and B ayesian cluster analyses suggest occasional gene flow over thousands of kilometres. Higher divergences between populations of C . gunnari as compared to C . aceratus are probably caused by lower dispersal capabilities and demographic effects. Bayesian skyline plots reveal population size reductions during past glacial events in both species with an estimated onset of population expansions about 25 000 years ago.