Population genetics and evolutionary history of some deep-sea demersal fishes from the Azores - North Atlantic

Abstract

MtDNA sequences and microsatellite loci were used as independent molecular markers to reveal the genetic population structure in three deep-sea demersal fish species from the North Atlantic. In the Azores archipelago, the demersal fishery is the second most important after tuna and Helicolenus dactylopterus, Beryx splendens and Beryx decadactylus are among the most captured species. Partial sequences for the mitochondrial control region and cytochrome b gene were obtained for the three species using universal primers. The diversity encountered for these markers is consistent with diversity found on other marine fishes, except for B.decadactylus in which the d-loop and cyt b diversity was lower than expected.
Haplotype data indicated a strong genetic differentiation between Helicolenus dactylopterus NW, Cape Verde and NE Atlantic populations suggesting long distance colonisation processes by jump dispersal events along major oceanic currents. Eight microsatellite loci were developed for H.dactylopterus in order to resolve population structure at a finer intraregional scale (within Portuguese waters). Significant deviations from allelic frequencies expected under Hardy-Weinberg equilibrium were detected at several loci. Analysis of FIS revealed significant differences from zero as a result of heterozygote deficiency. Estimates of FST, RST and AMOVA were also significant, suggesting that the population structure of this species within Portuguese waters was not homogeneous. Pairwise comparisons of FST, RST and genetic distances (DSW and (s)2) between populations revealed a significant separation of the Azores and Peniche (continental Portugal) populations as well as a moderate differentiation among subpopulations of the Azores archipelago.
Beryx splendens and Beryx decadactylus are two congeneric species with many similarities in known biology. Analysis of haplotype data revealed striking differences in structure and history of the populations of these two species. MtDNA sequences confirmed that Beryx splendens is constituted by one panmitic population within the Northeast Atlantic as has been previously hypothesised by other authors. Surprisingly, indices of genetic diversity were lower in the closely-related B.decadactylus and there was a strong genetic differentiation between Cape Verde and the rest of the NE Atlantic populations when analysed for the same molecular markers. Differences found are discussed based on the limited knowledge of these species especially with respect to life history.
Population structure results are discussed in relation to historical and on-going hydrogeographic events. Evidence for the strong influence of several events previous to the last glacial maximum (LGM) on the population demographic history and evolution of deep-sea demersal fish species in the North Atlantic was found.

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