Document Type

Article

Publication Date

2005

Publication Title

Journal of Evolutionary Biology

Volume

18

First Page

1220

Last Page

1233

DOI

10.1111/j.1420-9101.2005.00935.x

Keywords

cutthroat trout, cytonuclear disequilibrium, hybrid swarm, linkage disequilibria, mating bias, rainbow trout, reproductive isolation, selection

Abstract

Although reinforcement should enhance reproductive barriers in sympatric species, sympatric trout species do hybridize. Using mitochondrial and nuclear species markers, we investigated hybridization directionality, hybrid mating biases, and selection against hybrids in 13 sympatric cutthroat and rainbow trout populations on Vancouver Island, Canada. Approximately 50% of the genotyped fish were hybrid (F1 or higher-order) and populations ranged from very recent (all F1 hybrids) to extremely advanced higher-order hybridization. Overall, interbreeding was reciprocal, although some populations showed directional hybridization. Pronounced cytonuclear disequilibrium in post-F1 hybrids indicated a remarkable mating bias not previously reported, which is most likely because of behavioural reproductive preferences. Selection against hybrids was observed in only two populations, indicative of extrinsic selection. Two populations were ‘hybrid swarms’, with a complete loss of reproductive isolation. The complex hybridization dynamics in this system represent a valuable natural experiment of the genetic and evolutionary implications of recent and on-going interspecific hybridization.

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