Population genetic structure in a deepwater fish Coryphaenoides rupestris: patterns and processes

We observed significant genetic structure in a widely distributed North Atlantic demersal deepwater fish, the roundnose grenadier Coryphaenoides rupestris (Pisces: Macrouridae). The overall estimate of genetic differentiation, based on 6 microsatellite loci (F-ST = 0.0152; p < 0.0001), was elevated by samples from the periphery of the species' range, off Norway and Canada. Samples from the central area of distribution showed less pronounced genetic structure, indicating more extensive dispersal and gene flow. Simulations were run to assess expected patterns of genetic differentiation under 2 major hypotheses of gene flow: passive larval drift and demographic diffusion. In spite of the relatively long duration of the pelagic egg and juvenile phases, no correlation was found between observed pairwise F-ST values and those predicted under the hypothesis of drift of progeny by ocean currents. The observed pattern may instead arise from a combination of bathymetric barriers limiting deep pelagic mixing and advection, early life ontogenetic changes in vertical distribution, and limited migration once a benthopelagic life style has been established.