Asymmetrical male-mediated gene flow between harbor seal (Phoca vitulina) populations in Alaska

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Abstract:

Harbor seals (Phoca vitulina richardii (Gray, 1864)) in Alaska are currently treated as three distinct management stocks. Previous genetic analyses using mitochondrial DNA suggested that these stocks are differentiated genetically. We studied populations in Glacier Bay (GB; Southeast Alaska Stock), where harbor seals are declining, and Prince William Sound (PWS; Gulf of Alaska Stock), where the population has recently stabilized. Using six pairs of hypervariable microsatellite primers, we determined that these populations are a single panmictic unit with estimated migration rates of 22 animals/generation (PWS to GB) and 63 animals/generation (GB to PWS). The asymmetrical gene flow between GB and PWS is likely driven in part by a recent increase in competitors and predators of seals in GB. In contrast with males, emigration of females from PWS to GB (8.3 seals/generation) is higher than emigration of females from GB to PWS (3.3 seals/generation), likely because females use glacial ice as pupping habitat. Despite the high gene flow, the number of migrants per year (0.02% of the Gulf of Alaska population) is likely too low to influence the demographics of harbor seals in PWS, and the two populations may best be managed as separate stocks.

On considère actuellement que les phoques communs (Phoca vitulina richardii (Gray, 1864)) de l’Alaska forment trois stocks de gestion distincts. Des analyses génétiques antérieures basées sur l’ADN mitochondrial indiquent une différenciation génétique entre ces stocks. Nous étudions la population de Glacier Bay (GB, stock du sud-est de l’Alaska) où les phoques communs sont en déclin et celle du détroit du Prince William (PWS, stock du golfe de l’Alaska) qui s’est récemment stabilisée. À l’aide de six paires d’amorces microsatellites très variables, nous démontrons que ces populations forment une seule unité panmictique avec des taux estimés de migration de 22 animaux/génération (PWS à GB) et de 63 animaux/génération (GB à PWS). Ce flux génique asymétrique entre GB et PWS s’explique vraisemblablement en partie par une augmentation récente des compétiteurs et des prédateurs des phoques dans GB. Contrairement à celle des mâles, l’émigration des femelles de PWS à GB (8,3 phoques/génération) est plus importante que l’émigration de femelles de GB à PWS (3,3 phoques/génération), vraisemblablement parce que les femelles utilisent la glace glaciaire comme habitat de mise bas. Malgré ce flux génique élevé, le nombre annuel de migrateurs (0,02 % de la population du golfe de l’Alaska) est vraisemblablement trop faible pour affecter la démographie des phoques communs de PWS, et il vaut mieux gérer les deux populations comme des stocks distincts.

Document Type: Research Article

Publication date: June 1, 2009

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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