Population genetic structure and gene flow patterns between populations of the Antarctic icefish Chionodraco rastrospinosus

Aim  A lack of genetic structure is predicted for Antarctic fish due to the duration of pelagic larval stages and the strength of the currents in the Southern Ocean, particularly the Antarctic Circumpolar Current. In this study we explored the population structure of the ocellated icefish, Chionodraco rastrospinosus, by means of analysing a total of 394 individuals collected at four geographical areas off the Antarctic Peninsula in the period 1996–2006. Location  Elephant Island, southern South Shetlands, Joinville Island and South Orkneys in the Southern Ocean. Methods  The spatio-temporal genetic structure of Chionodraco rastrospinosus was explored using seven microsatellite loci. Existence and direction of gene flow across sampling locations were investigated using the isolation-by-migration procedure. Results  Microsatellite data showed a lack of genetic structuring in the area studied, with no differences found at both the geographical or temporal level, and an eastward unidirectional gene flow among sites. This suggested a lack of genetic barriers for this species, attributable to larval dispersal following the Antarctic Circumpolar Current, which fits well with the predicted pattern for Antarctic fish. Re-examination of genetic data of the closely related icefish Chaenocephalus aceratus, with similar larval duration but displaying genetically structured populations, indicated a weak but significant bidirectional gene flow. Main conclusions  Our results point to a relationship that is more complex than expected between potential for dispersal and realized gene flow in the marine environment. In addition to ocean circulation and larval dispersal, other major life-history traits might be driving connectivity, particularly larval retention.