Evaluating the influence of stocking history and barriers to movement on the spatial extent of hybridization between westslope cutthroat trout and rainbow trout

In this study we examine how the stocking of rainbow trout (Oncorhynchus mykiss), as well as the presence of fish movement barriers, influences the probability of introgression with westslope cutthroat trout (Oncorhynchus clarkii lewisi). We measured the level of introgression in cutthroat trout sampled from 32 locations that occurred either above or below fish movement barriers along with the frequency and number of rainbow trout stocked in the watershed over a 43-year period. The occurrence and level of hybridization in cutthroat trout were not related to whether the site was above a movement barrier or not. In contrast, the level of introgression was related to the distance to the nearest stocking location, the number of stocking events within the nearest watershed, and the total number of rainbow trout stocked in that watershed. Our data indicate that westslope cutthroat trout located further from stocking have a lower risk of introgression with rainbow trout, but those isolated above movement barriers should not be considered free from introgression until a thorough genetic assessment of the location has been made.

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Spatial and temporal spawning dynamics of native westslope cutthroat trout, Oncorhynchus clarkii lewisi, introduced rainbow trout, Oncorhynchus mykiss, and their hybrids

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f09-073 ◽

2009 ◽

Vol 66 (7) ◽

pp. 1153-1168 ◽

Cited By ~ 44

Author(s):

Clint C. Muhlfeld ◽

Thomas E. McMahon ◽

Durae Belcer ◽

Jeffrey L. Kershner

Keyword(s):

Rainbow Trout ◽

Oncorhynchus Mykiss ◽

Cutthroat Trout ◽

River System ◽

Westslope Cutthroat Trout ◽

Time And Space ◽

Long Distance ◽

Oncorhynchus Clarkii ◽

Rainbow Trout Oncorhynchus Mykiss ◽

Spring Runoff

We used radiotelemetry to assess spatial and temporal spawning distributions of native westslope cutthroat trout ( Oncorhynchus clarkii lewisi ; WCT), introduced rainbow trout ( Oncorhynchus mykiss ; RBT), and their hybrids in the upper Flathead River system, Montana (USA) and British Columbia (Canada), from 2000 to 2007. Radio-tagged trout (N = 125) moved upriver towards spawning sites as flows increased during spring runoff and spawned in 29 tributaries. WCT migrated greater distances and spawned in headwater streams during peak flows and as flows declined, whereas RBT and RBT hybrids (backcrosses to RBT) spawned earlier during increasing flows and lower in the system. WCT hybrids (backcrosses to WCT) spawned intermediately in time and space to WCT and RBT and RBT hybrids. Both hybrid groups and RBT, however, spawned over time periods that produced temporal overlap with spawning WCT in most years. Our data indicate that hybridization is spreading via long-distance movements of individuals with high amounts of RBT admixture into WCT streams and stepping-stone invasion at small scales by later generation backcrosses. This study provides evidence that hybridization increases the likelihood of reproductive overlap in time and space, promoting extinction by introgression, and that the spread of hybridization is likely to continue if hybrid source populations are not reduced or eliminated.

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Cold tolerance performance of westslope cutthroat trout (Oncorhynchus clarkii lewisi) and rainbow trout (Oncorhynchus mykiss) and its potential role in influencing interspecific hybridization

Canadian Journal of Zoology ◽

10.1139/cjz-2014-0047 ◽

2014 ◽

Vol 92 (9) ◽

pp. 777-784 ◽

Cited By ~ 6

Author(s):

M.M. Yau ◽

E.B. Taylor

Keyword(s):

Rainbow Trout ◽

Oncorhynchus Mykiss ◽

Water Temperature ◽

Cold Water ◽

Cutthroat Trout ◽

Acclimation Temperature ◽

Westslope Cutthroat Trout ◽

Oncorhynchus Clarkii ◽

Rainbow Trout Oncorhynchus Mykiss ◽

Differential Adaptation

Hybridization between rainbow trout (Oncorhynchus mykiss (Walbaum, 1792)) and westslope cutthroat trout (Oncorhynchus clarkii lewisi (Girard, 1856)) occurs commonly when rainbow trout are introduced into the range of westslope cutthroat trout. Typically, hybridization is most common in warmer, lower elevation habitats, but much less common in colder, higher elevation habitats. We assessed the tolerance to cold water temperature (i.e., critical thermal minimum, CTMin) in juvenile rainbow trout and westslope cutthroat trout to test the hypothesis that westslope cutthroat trout better tolerate low water temperature, which may explain the lower prevalence of rainbow trout and interspecific hybrids in higher elevation, cold-water habitats (i.e., the “elevation refuge hypothesis”). All fish had significantly lower CTMin values (i.e., were better able to tolerate low temperatures) when they were acclimated to 15 °C (mean CTMin = 1.37 °C) versus 18 °C (mean CTMin = 1.91 °C; p < 0.001). Westslope cutthroat trout tended to have lower CTMin than rainbow trout from two populations, second–generation (F2) hybrids between two rainbow trout populations, and backcrossed rainbow trout at 15 °C (cross type × acclimation temperature interaction; p = 0.018). Differential adaptation to cold water temperatures may play a role in influencing the spatial distribution of hybridization between sympatric species of trout.

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

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f08-001 ◽

2008 ◽

Vol 65 (4) ◽

pp. 658-669 ◽

Cited By ~ 81

Author(s):

Matthew C Boyer ◽

Clint C Muhlfeld ◽

Fred W Allendorf

Keyword(s):

Gene Flow ◽

Rainbow Trout ◽

Oncorhynchus Mykiss ◽

Microsatellite Loci ◽

Cutthroat Trout ◽

Conservation Strategy ◽

Westslope Cutthroat Trout ◽

Hybrid Swarm ◽

Oncorhynchus Clarkii ◽

Rainbow Trout Oncorhynchus Mykiss

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 (θST = 0.076, ρST = 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.

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Morphological and swimming stamina differences between Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri), rainbow trout (Oncorhynchus mykiss), and their hybrids

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f06-175 ◽

2007 ◽

Vol 64 (1) ◽

pp. 127-135 ◽

Cited By ~ 34

Author(s):

Steven M Seiler ◽

Ernest R Keeley

Keyword(s):

Rainbow Trout ◽

Oncorhynchus Mykiss ◽

Body Shape ◽

Cutthroat Trout ◽

Swimming Velocity ◽

Swimming Ability ◽

Geometric Morphometric ◽

Oncorhynchus Clarkii ◽

Rainbow Trout Oncorhynchus Mykiss ◽

Yellowstone Cutthroat Trout

We hypothesized that body shape differences between Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri), rainbow trout (Oncorhynchus mykiss), and their hybrids may influence swimming ability and thus play an important role in the invasion of nonnative rainbow trout and hybrid trout into native cutthroat trout populations. We reared Yellowstone cutthroat trout, rainbow trout, and reciprocal hybrid crosses in a common environment and conducted sustained swimming trials in order to test for genetically based morphological and swimming stamina differences. Linear and geometric morphometric analyses identified differences in body shape, with cutthroat trout having slender bodies and small caudal peduncles and rainbow trout having deep bodies and long caudal peduncles. Hybrid crosses were morphologically intermediate to the parental genotypes, with a considerable maternal effect. Consistent with morphological differences, cutthroat trout had the lowest sustained swimming velocity and rainbow trout had the highest sustained swimming velocity. Sustained swimming ability of hybrid genotypes was not different from that of rainbow trout. Our results suggest that introduced rainbow trout and cutthroat-rainbow trout hybrids potentially out-compete native Yellowstone cutthroat trout through higher sustained swimming ability.

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