Abstract
Population genetic studies of species inhabiting the deepest parts of the oceans are still scarce and only until recently we started to understand how oceanographic processes and topography affect dispersal and gene flow patterns. The aim of this study was to investigate the spatial population genetic structure of the bathyal bony fish Coryphaenoides mediterraneus, with a focus on the AtlanticâMediterranean transition. We used nine nuclear microsatellites and the mitochondrial cytochrome c oxidase I gene from 6 different sampling areas. No population genetic structure was found within Mediterranean with both marker types (mean ΊST = 0.0960, FST = -0.0003, for both P > 0.05). However, within the Atlantic a contrasting pattern of genetic structure was found for the mtDNA and nuclear markers (mean ΊST = 0.2479, P < 0.001; FST = -0.0001, P > 0.05). When comparing samples from Atlantic and Mediterranean they exhibited high and significant levels of genetic divergence (mean ΊST = 0.7171, FST = 0.0245, for both P < 0.001) regardless the genetic marker used. Furthermore, no shared haplotypes were found between Atlantic and Mediterranean populations. These results suggest very limited genetic exchange between Atlantic and Mediterranean populations of C. mediterraneus, likely due to the shallow bathymetry of the Strait of Gibraltar acting as a barrier to gene flow. This physical barrier not only prevents the direct interactions between the deep-living adults, but also must prevent interchange of pelagic early life stages between the two basins. According to Bayesian simulations it is likely that Atlantic and Mediterranean populations of C. mediterraneus were separated during the late Pleistocene, which is congruent with results for other deep-sea fish from the same region.
Highlights
Population genetic studies of species inhabiting the deepest parts of the oceans are still scarce compared to shallow or coastal water relatives
Considering only MidAtlantic Ridge (MAR) sites, despite the approximately same number of individuals analysed in the north (MAR1, n = 30) and in the south (MAR3, n = 38) the haplotype diversity was much lower in the north (Hn = 0.000, as only the H2 haplotype was observed at MAR1, see Fig 1) than in the south (Hn = 0.542; Table 2)
The results obtained for the Mediterranean grenadier suggest the existence of a genetic barrier between Atlantic and Mediterranean populations
Summary
Population genetic studies of species inhabiting the deepest parts of the oceans are still scarce compared to shallow or coastal water relatives. The deep-sea is historically described as a stable and homogeneous environment where the existence of barriers to dispersal and gene flow among populations are less evident [1] Some studies support this pattern since genetic homogeneity over large spatial scales of several deep-sea species seems to prevail, for example the wreckfish (Polyprion americanus [2]), the hydrothermal vent shrimp (Rimicaris exoculata, [3]), the black scabbardfish (Aphanopus carbo, [4]), the blue hake (Antimora rostrata, [5]) and the orange roughy (Hoplostethus atlanticus, [6]). The Modified Atlantic Water enters the Mediterranean while at deeper layers, the Intermediate Mediterranean Water (denser and saltier) flows toward the Atlantic [13]
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