Ecological consequences of hybridization between native westslope cutthroat (Oncorhynchus clarkii lewisi) and introduced rainbow (Oncorhynchus mykiss) trout: effects on life history and habitat use

2010 ◽  
Vol 67 (2) ◽  
pp. 357-370 ◽  
Author(s):  
Joseph B. Rasmussen ◽  
Michael D. Robinson ◽  
Daniel D. Heath
Keyword(s):  
Life History ◽  
Rainbow Trout ◽  
Oncorhynchus Mykiss ◽  
Cutthroat Trout ◽  
Oncorhynchus Clarkii ◽  
Metabolic Characteristics ◽  
Clear Cut ◽  
Genotype Frequencies ◽  
Physical Barriers ◽  
High Elevations

In the Upper Oldman River, Alberta, Canada, hybridization between introduced rainbow trout (RT; Oncorhynchus mykiss ) and native westslope cutthroat trout (WCT; Oncorhynchus clarkii lewisi ) has produced a genotypic gradient with rainbow trout alleles undetectable (<1%) at high elevations and increasing in abundance downstream. Few F1 hybrids were found, and genotype frequencies suggest strong backcrossing of hybrids to pure parental populations at both ends of the gradient. The increasing prevalence of RT alleles downstream is accompanied by a life history gradient such that RT alleles were positively associated with growth rate and negatively associated with survivorship. Although physical barriers extended the distribution of pure WCT downstream, several streams held genetically pure WCT in their uppermost reaches, even when no barriers were present. For example, RT alleles were undetectable in headwaters of Dutch Creek, which had no barriers but was very cold (average summer temperature <7.3 °C). We propose that RT alleles affect the choice of habitat, as well the metabolic characteristics that determine their life history and competitive abilities. Factors such as climate change, clear-cut logging, and anthropogenic enrichment that can lead to increased temperature and (or) productivity might be expected to result in an upstream shift of RT alleles.

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

2009 ◽  
Vol 66 (7) ◽  
pp. 1153-1168 ◽  
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.

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

2014 ◽  
Vol 92 (9) ◽  
pp. 777-784 ◽  
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.

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

2007 ◽  
Vol 64 (1) ◽  
pp. 127-135 ◽  
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.

Hybridization with rainbow trout alters life history traits of native westslope cutthroat trout

2013 ◽  
Vol 70 (6) ◽  
pp. 895-904 ◽  
Author(s):  
Matthew P. Corsi ◽  
Lisa A. Eby ◽  
Craig A. Barfoot
Keyword(s):  
Life History ◽  
Rainbow Trout ◽  
Negative Relationship ◽  
Somatic Growth ◽  
Cutthroat Trout ◽  
Westslope Cutthroat Trout ◽  
Oncorhynchus Clarkii ◽  
Migration Timing ◽  
Linear Relationships ◽  
And Migration

Hybridization with rainbow trout is a primary threat to the conservation of westslope cutthroat trout (Oncorhynchus clarkii lewisi; hereafter cutthroat) across its native range. Cutthroat conservation policy hinges on the degree to which populations are hybridized, yet little is known about differences in the life history of individuals with varying degrees of rainbow trout ancestry. We examined differences in growth, fecundity, and migration timing between cutthroat and hybrid trout in migratory components of populations from 2006 to 2009 in the Jocko River, Montana. We detected positive linear relationships between rainbow trout ancestry and somatic growth and egg size, but a negative relationship with fecundity. US federal policy suggests a threshold of 20% rainbow ancestry for cutthroat conservation. In our study, hybrids with ≥20% rainbow trout ancestry had significantly lower fecundity and larger egg sizes and migrated earlier at lower discharges and stream temperatures than individuals with <20% rainbow trout ancestry. Our results did not indicate threshold changes but rather continuous differences associated with rainbow trout ancestry, suggesting that establishing a biologically relevant cutoff for conservation purposes will be problematic.

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

2008 ◽  
Vol 65 (4) ◽  
pp. 658-669 ◽  
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.

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

2014 ◽  
Vol 71 (7) ◽  
pp. 1050-1058 ◽  
Author(s):  
Janet L. Loxterman ◽  
Ernest R. Keeley ◽  
Zacharia M. Njoroge
Keyword(s):  
Rainbow Trout ◽  
Oncorhynchus Mykiss ◽  
Lower Risk ◽  
Cutthroat Trout ◽  
Spatial Extent ◽  
Fish Movement ◽  
Westslope Cutthroat Trout ◽  
Oncorhynchus Clarkii ◽  
Rainbow Trout Oncorhynchus Mykiss ◽  
Genetic Assessment

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.

Cutthroat Trout: Evolutionary Biology and Taxonomy

2018 ◽  
Keyword(s):  
Rainbow Trout ◽  
Rocky Mountains ◽  
Evolutionary Biology ◽  
Cutthroat Trout ◽  
Taxonomic Revision ◽  
River Basins ◽  
Evidence Based ◽  
Oncorhynchus Clarkii ◽  
Southern Rocky Mountains ◽  
Green Lineage

<em>Abstract</em>.—One objective of systematics is to recognize species in a manner that minimizes the disparity between species as real entities in nature and species as a Linnaean category. Reconciliation requires a conceptualization of species consistent with evolutionary processes that yields predictive delimitation criteria. Here we review the unified species concept (USC) and its associated delimitation criteria as a prelude to revising the taxonomy of Cutthroat Trout <em>Oncorhynchus clarkii</em>. Additionally, in the context of the conceptualizing species as a separately evolving metapopulation, we briefly review how climate change may have influenced the connectivity and isolation of Cutthroat Trout within and among river basins, with a focus mainly on the Cutthroat Trout of the Southern Rocky Mountains. We summarize evidence based on delimitation criteria that distinguishes Rainbow Trout <em>O. mykiss</em> and Cutthroat Trout, Gila Trout<em> O. gilae </em>and Rainbow Trout, and blue lineage and green lineage Cutthroat Trout from the Southern Rocky Mountains. We advocate adopting the USC as a guide for taxonomic revision of Cutthroat Trout, recommend eliminating subspecies as a valid taxonomic designation, and expect—based on our evaluation of three pairs of species—that the taxonomy of Cutthroat Trout will be revised in ways that elevate some recognized subspecies to species status.

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