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Rainbow trout (Oncorhynchus mykiss) invasion and the spread of hybridization with native westslope cutthroat trout (Oncorhynchus clarkii lewisi)

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Abstract:

We analyzed 13 microsatellite loci to estimate gene flow among westslope cutthroat trout, Oncorhynchus clarkii lewisi, populations and determine the invasion pattern of hybrids between native O. c. lewisi and introduced rainbow trout, Oncorhynchus mykiss, in streams of the upper Flathead River system, Montana (USA) and British Columbia (Canada). Fourteen of 31 sites lacked evidence of O. mykiss introgression, and gene flow among these nonhybridized O. c. lewisi populations was low, as indicated by significant allele frequency divergence among populations (ST = 0.076, ST = 0.094, P < 0.001). Among hybridized sites, O. mykiss admixture declined with upstream distance from a site containing a hybrid swarm with a predominant (92%) O. mykiss genetic contribution. The spatial distribution of hybrid genotypes at seven diagnostic microsatellite loci revealed that O. mykiss invasion is facilitated by both long distance dispersal from this hybrid swarm and stepping-stone dispersal between hybridized populations. This study provides an example of how increased straying rates in the invasive taxon can contribute to the spread of extinction by hybridization and suggests that eradicating sources of introgression may be a useful conservation strategy for protecting species threatened with genomic extinction.

L’analyse de 13 locus microsatellites nous permet d’estimer le flux génique au sein de populations de truites fardées du versant occidental, Oncorhynchus clarkii lewisi, et de déterminer les patrons d’invasion des hybrides entre les O. c. lewisi indigènes et les truites arc-en-ciel, Oncorhynchus mykiss, introduites dans les cours d’eau du bassin supérieur de la Flathead, Montana (É.-U.) et la Colombie Britannique (Canada). Quatorze des 31 sites ne montrent aucun signe d’introgression d’O. mykiss et le flux génique entre ces populations non hybrides d’O. c. lewisi est faible, tel que l’indique la divergence significative des fréquences d’allèles dans les populations (ST = 0,076, ST = 0,094; P < 0,001). Dans les sites présentant de l’hybridation, l’admixtion d’O. mykiss diminue en fonction de la distance vers l’aval à partir d’un site qui contient un rassemblement d’hybrides avec une contribution génétique prédominante (92 %) d’O. mykiss. La répartition spatiale des génotypes hybrides à sept locus microsatellites diagnostics indique que l’invasion d’O. mykiss est facilitée autant par la dispersion à longue distance depuis le rassemblement d’hybrides que par une dispersion en escalier entre les populations hybrides. Notre étude fournit un exemple qui montre comment les taux accrus d’errance d’un taxon envahissant peuvent contribuer à la diffusion de l’extinction par hybridation et elle laisse croire que l’éradication des sources d’introgression peut être une stratégie utile de conservation pour protéger les espèces menacées d’extinction génomique.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: April 1, 2008

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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