Introgressive Hybridization Between Native Cutthroat Trout and Introduced Rainbow Trout

Abstract

Introgressive hybridization threatens the persistence of several species of native salmonids in the western United States, but little is known about the factors influencing the establishment and maintenance of introgressed populations. We examined the occurrence of introgressive hybridization in westslope cutthroat (Oncorhynchus clarki lewisi) and rainbow trout (O. mykiss) populations in relation to physical characteristics of streams, trout density estimates, and the distance from stocking source. Trout were sampled from 80 stream sites in the Clearwater River Basin, Idaho, USA, and tissues from individual trout were analyzed to detect hybridization using noncoding sequences of nuclear DNA. We found a broad zone of hybridization detected at 64% of the sampled sites. The presence and degree of introgression was negatively related to elevation and positively related to stream width in our logistic regression model. Stream elevation and size likely influence hydrologic and thermal regimes. An interaction between the life history characteristics of the native and nonnative trout with these hydrologic and thermal stream gradients could explain the invasion success of rainbow trout and hence, the extent of the hybrid zone. Alternatively, the influence of elevation and stream width could be the result of habitat selection by the parental species, thereby reducing the opportunity for hybridization. Understanding the relationship between abiotic factors and introgressive hybridization will assist fisheries managers when evaluating the potential threat of introgression in different stream habitats and applying the necessary management actions to conserve the native cutthroat trout genotypes across broad landscapes. Corresponding Editor: K. D. Fausch

Establishment, Persistence, and Introgression of Entomopathogenic Nematodes in a Forest Ecosystem

“…Indirect effects such as competitive displacement and/or hybridization are possible risks associated with the introduction of exotic species, including EPN (Ellstrand et al 1999, van Lenteren et al 2003, Weigel et al 2003. Strains of a species may differ in virulence, reproductive capacity, and environmental tolerance (Somasekhar et al 2002b), and there is a risk that exotic strains might competitively displace native strains of the same species.…”

An Evaluation of Angler Harvest of Walleye and Saugeye in a Kansas Reservoir

“…Perry et al (2002) provide a thorough discussion and review of hybridization in freshwater systems and suggested that hybridization is one of the most important factors associated with the poor status of aquatic organisms. For example, hybridization of cutthroat trout (Oncorhynchus clarki) with rainbow trout (0. mykiss) is a primary threat to the persistence of cutthroat trout (Weigel et al 2003). Similar concerns have been expressed for a variety of aquatic and terrestrial organisms (Rhymer and Simberloff 1996, Allendorf et al 2001, Perry et al 2002.…”

Evaluate the Life History of Native Salmonids in the Malheur Subbasin, Fiscal Year 2008 Annual Report.

“…Recent studies of hybridization between other native and introduced salmonids have demonstrated that oftentimes the pattern of hybridization within a stream network is not random and that the extent of hybridization within a stream can be influenced by a number of biotic and abiotic factors (Weigel et al 2003;Bettles et al 2005;Rubidge and Taylor 2005;Boyer et al 2008;Gunnell et al 2008). Given these results, a more thorough examination of the spatial patterns of hybridization between bull trout and brook trout is warranted.…”