Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 9027
Title: Introgression among three rockfish species (Sebastes spp.) In the Salish Sea, Northeast Pacific Ocean
Author: P. L. Schwenke, Linda K. Park, L. Hauser
Publication Year: 2018
Journal: PLoS ONE
Volume: 13
Issue: 3
Pages: e0194068

Interspecific hybridization is often seen as a major conservation issue, potentially threatening endangered species and decreasing biodiversity.  In natural populations, the conservation implications of hybridization depends on both on anthropogenic factors and the evolutionary processes maintaining the hybrid zone. However, the timeline and patterns of hybridization in the hybrid zone are often not known. Therefore, species conservation becomes a concern when recent anthropogenic changes influence hybridization and not if hybridization is part of a long-term process.  Here, we use sequence data from one mitochondrial gene, three nuclear introns and one nuclear exon to estimate the direction, geographic extent, frequency and possible timeline of hybridization between three rockfish species (Sebastes auriculatus, S. caurinus, S. malliger) in the Salish Sea, Washington, USA. We show that (i) introgression occurred in the Salish Sea, but not outside on the outer coast, (ii) introgression was highly asymmetrical from S. maliger into the other two species, (iii) almost 40% of individuals in the Salish Sea were hybrids, with frequency of hybrids increasing with isolation from the coast, and (iv) all hybrids were later generation backcrosses rather than F1 hybrids. Our results suggest long-standing low-level hybridization rather than recent onset of interbreeding because of human induced environmental change, possibly facilitated by specific environmental conditions in the sub-basins of the Salish Sea, and by differences in population sizes during recolonization of the area after the last glaciation.  This rockfish hybrid system, with asymmetrical introgression and the maintenance of parental species, may prove useful to study both mechanisms that maintain species boundaries and that facilitate speciation in the presence of rapid environmental change.

Theme: Recovery and rebuilding of marine and coastal species
Foci: Characterize the population biology of species, and develop and improve methods for predicting the status of populations.