Genetic panmixia and demographic dependence across the North Atlantic in the deep-sea fish, blue hake (Antimora rostrata)

Abstract

The efficient investment of resources and effort into conservation strategies depends on the accurate identification of management units. At the same time, understanding the processes by which population structure evolves requires an understanding of the conditions under which panmixia may exist. Here, we study a species with an unusual, apparently sex-biased pattern of distribution, and test the hypothesis that distribution processes associated with this pattern (for example, congregating at a single dominant spawning site or periodic mixing during reproduction) could lead to panmixia over a large geographic range. Using 13 microsatellite markers, we compared 393 blue hake (Antimora rostrata) from 11 sample sites across a geographic range of over 3000 km, and found no evidence of population structure. We estimated current effective population size and found it to be large (~15,000) across the sampled area. In addition, we used simulation models to test expectations about demographic correlation among populations and our ability to detect relevant levels of gene flow. All data were consistent with the interpretation of long-range panmixia.

Figure 1

Sample sites in the North Atlantic. Gray scale shading denotes height above sea level in meters. Dashed line shows approximate location of the sub-polar front. The top left of the map is 70°N, 70°W, and the bottom right is 40°N, 10°E.

Figure 2

The consequences of migration for the fates of two populations, one of which is harvested. (a–c) Final population sizes following a 20-year simulation in which one population (broken line) is harvested and the other (solid line) is not (lines show average over 5000 Monte Carlo simulations). (d–f) Mean correlation (Pearson's r) between the two populations over 100 years of simulation (averaged over 1000 Monte Carlo simulations). See Materials and methods for further details. K̄=250 000, σ=0.1 in all simulations. Intrinsic rate of population growth, r, and rate at which population (b) was harvested, h_B, increase from left to right: (a, d) r=0.1, h_B=0.16; (b, e) r=0.5, h_B=0.38; (c, f) r=0.9, h_B=0.56. Shaded areas show 95% confidence intervals for simulation outcomes.