Abstract
The Kerguelen archipelago, isolated in the Southern Ocean, shelters a blue mussel Mytilus metapopulation far from any influence of continental populations or any known hybrid zone. The finely carved coast leads to a highly heterogeneous habitat. We investigated the impact of the environment on the genetic structure in those Kerguelen blue mussels by relating allele frequencies to habitat descriptors. A total sample comprising up to 2248 individuals from 35 locations was characterized using two nuclear markers, mac-1 and Glu-5′, and a mitochondrial marker (COI). The frequency data from 9 allozyme loci in 9 of these locations were also reanalyzed. Two other nuclear markers (EFbis and EFprem's) were monomorphic. Compared to Northern Hemisphere populations, polymorphism in Kerguelen blue mussels was lower for all markers except for the exon Glu-5′. At Glu-5′, genetic differences were observed between samples from distinct regions (FCT = 0.077), as well as within two regions, including between samples separated by <500 m. No significant differentiation was observed in the AMOVA analyses at the two other markers (mac-1 and COI). Like mac-1, all allozyme loci genotyped in a previous publication, displayed lower differentiation (Jost's D) and FST values than Glu-5′. Power simulations and confidence intervals support that Glu-5′ displays significantly higher differentiation than the other loci (except a single allozyme for which confidence intervals overlap). AMOVA analyses revealed significant effects of the giant kelp Macrocystis and wave exposure on this marker. We discuss the influence of hydrological conditions on the genetic differentiation among regions. In marine organisms with high fecundity and high dispersal potential, gene flow tends to erase differentiation, but this study showed significant differentiation at very small distance. This may be explained by the particular hydrology and the carved coastline of the Kerguelen archipelago, together with spatially variable selection at Glu-5′.
Highlights
In marine benthic organisms, a long planktonic larval stage generally allows gene flow between remote populations and neutral genetic differentiation increases only slightly with geographical distance (Launey et al 2002)
To determine whether the genetic polymorphism of the blue mussel population of Kerguelen is driven by neutral and/or adaptive forces, we (i) investigated the influence of the water circulation around Kerguelen, first on the total genetic structure and second within differentiated groups and (ii) tested the influence of the habitat type at a smaller scale. To fill in these objectives, we used two nuclear markers polymorphic in Kerguelen blue mussels: Glu-50 (Inoue et al 1995; Rawson et al 1996) and mac-1 (Ohresser et al 1997), and we considered the sequence polymorphism at the mitochondrial DNA locus COI (Gerard et al 2008)
The locus mac-1 is the first intron of the Mytilus actin protein (Ohresser et al 1997)
Summary
A long planktonic larval stage generally allows gene flow between remote populations and neutral genetic differentiation increases only slightly with geographical distance (Launey et al 2002). Physical isolation (e.g., large distances, oceanic fronts, gyres) enhances genetic differences among populations. Differentiation may arise locally through adaptation to localized environmental conditions (Maynard Smith 1966; Barton and Hewitt 1985). Detecting adaptation through natural selection is difficult a 2015 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd. Ecology and Evolution published by John Wiley & Sons Ltd
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