Behavioral, Ecological, and Fitness Consequences of Hybridization Between Native Westslope Cutthroat Trout (Oncorhynchus Clarkii Lewisi) and Nonnative Rainbow Trout (O. Mykiss) PDF Download
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Author: Clint Cain Muhlfeld Publisher: ISBN: Category : Animal ecology Languages : en Pages : 264
Book Description
Anthropogenic hybridization is one of the greatest threats to global biodiversity. Hybridization and introgression may lead to a loss of locally adapted gene complexes and ecological adaptations in native populations, yet these potential consequences have not been fully evaluated in nature. I investigated factors influencing the spread of hybridization between native westslope cutthroat trout (Oncorhynchus clarkii lewisi) and nonnative rainbow trout (O. mykiss) in the upper Flathead River system, Montana (USA) and British Columbia (Canada). The fundamental questions of my dissertation were: what are the behavioral, ecological, and fitness consequences of hybridization and what factors influence successful invasion of hybrids? First, I assessed the patterns of spawning between parental species and their hybrids and found that hybridization alters the spawning behavior of migratory westslope cutthroat trout, and is spreading via long distance dispersal of hybrids from downstream sources and some temporal overlap during spawning. Second, I describe for the first time how a wide range of levels of nonnative admixture affect fitness of cutthroat trout in the wild by estimating reproductive success in a recently invaded stream using parentage analysis with multilocus microsatellite markers. Small amounts of hybridization markedly reduced reproductive success, with fitness exponentially declining by ~50% with 20% nonnative genetic admixture. Finally, I evaluated the association of local-habitat features, landscape characteristics, and biotic factors with the spread of hybridization in the system, and found that hybridization increases in streams with warmer water temperatures, high land use disturbance and close proximity to the source of hybridization; however, none of these factors appeared sufficient to prevent further spread. These combined results suggest that hybrids are not only genetically different than westslope cutthroat trout but also have reduced fitness and are ecologically different, and that hybridization is likely to continue to spread if hybrid populations with high amounts of rainbow trout admixture are not reduced or eliminated. I conclude that extant aboriginal cutthroat trout are at greater conservation risk due to hybridization than previously thought and policies that protect hybridized populations need reconsideration.
Author: Clint Cain Muhlfeld Publisher: ISBN: Category : Animal ecology Languages : en Pages : 264
Book Description
Anthropogenic hybridization is one of the greatest threats to global biodiversity. Hybridization and introgression may lead to a loss of locally adapted gene complexes and ecological adaptations in native populations, yet these potential consequences have not been fully evaluated in nature. I investigated factors influencing the spread of hybridization between native westslope cutthroat trout (Oncorhynchus clarkii lewisi) and nonnative rainbow trout (O. mykiss) in the upper Flathead River system, Montana (USA) and British Columbia (Canada). The fundamental questions of my dissertation were: what are the behavioral, ecological, and fitness consequences of hybridization and what factors influence successful invasion of hybrids? First, I assessed the patterns of spawning between parental species and their hybrids and found that hybridization alters the spawning behavior of migratory westslope cutthroat trout, and is spreading via long distance dispersal of hybrids from downstream sources and some temporal overlap during spawning. Second, I describe for the first time how a wide range of levels of nonnative admixture affect fitness of cutthroat trout in the wild by estimating reproductive success in a recently invaded stream using parentage analysis with multilocus microsatellite markers. Small amounts of hybridization markedly reduced reproductive success, with fitness exponentially declining by ~50% with 20% nonnative genetic admixture. Finally, I evaluated the association of local-habitat features, landscape characteristics, and biotic factors with the spread of hybridization in the system, and found that hybridization increases in streams with warmer water temperatures, high land use disturbance and close proximity to the source of hybridization; however, none of these factors appeared sufficient to prevent further spread. These combined results suggest that hybrids are not only genetically different than westslope cutthroat trout but also have reduced fitness and are ecologically different, and that hybridization is likely to continue to spread if hybrid populations with high amounts of rainbow trout admixture are not reduced or eliminated. I conclude that extant aboriginal cutthroat trout are at greater conservation risk due to hybridization than previously thought and policies that protect hybridized populations need reconsideration.
Author: Matthew Corsi Publisher: ISBN: Category : Cutthroat trout Languages : en Pages :
Book Description
The role of introductions of nonnative fishes in the decline of native fishes cannot be overstated. Westslope cutthroat trout (Oncorhynchus clarkii lewisi, WCT) are a salmonid native to the northern Rocky Mountains. These trout hybridize with rainbow trout (O. mykiss, RBT) where they are sympatric; however, in portions of the WCT range where RBT have been introduced, hybridization appears to spread rapidly and threatens continued existence of WCT. The conservation value of these hybridized populations is equivocal, and a better knowledge of the ecological, demographic, behavioral, and genetic consequences of hybridization is needed to better inform conservation strategies. I investigated three related questions: specifically, what landscape factors are associated with estimates of introgression; what are life history differences between WCT and hybrids; and what are tradeoffs in restoring migratory life history in populations threatened by hybridization? The riverscape context plays a substantial role in the distribution of hybrids, as estimates of introgression declined with increases in stream slope, elevation, and distance from a primary source of RBT, three correlated landscape variables. Spatial variation in patterns of hybridization suggests clarifying objectives for sampling and careful designs are necessary to adequately understand the status of populations. Variation in location may relate to some of the ecological differences, such as growth, among fish with different levels of introgression. In the Jocko River, hybrids with ancestry> 20% RBT demonstrated higher growth, earlier migration, increased egg size, and lower fecundity versus WCT. These lines of evidence demonstrate the importance of limiting further hybridization even in populations that already have low levels of hybridization. Given that many unaltered populations currently reside in isolated habitat fragments, I evaluated several demographic tradeoffs of restoring a migratory life history weighed against the risks of increased potential for hybridization from removing barriers or selectively passing migratory fish above the barriers using both matrix and genetic population models. Restoration of migratory life history substantially increases population viability; however, hybridization in above-barrier population increases predictably relative to hybridization status of below-barrier population, which may reduce viability if vital rates are reduced in hybrids. Hybridization creates a challenging set of management problems, but this research adds several important pieces to the puzzles to help develop and evaluate conservation strategies.
Author: Daniel P. Drinan Publisher: ISBN: Category : Languages : en Pages : 213
Book Description
Hybridization is an important and common evolutionary process that can contribute to diversification, adaptation, and speciation. When species hybridize, divergent genomes are combined through recombination and may result in phenotypic changes. Such phenotypic changes may be the result of differences in chromosomal structure or adaptive divergence between the parental species and may ultimately affect fitness. Understanding how phenotypes change following hybridization, as well as the genetic mechanisms responsible for changes is critical for understanding divergent selection, speciation, and identifying populations that may be at risk from hybridization. Here, the effect of hybridization between cutthroat (Oncorhynchus clarkii) and rainbow trout (O. mykiss) on fitness was investigated using three techniques. In the first chapter, fitness influencing traits were compared among individuals at various hybridization levels. In the second chapter, genomic changes that could affect fitness were identified in the hybrid relative to rainbow trout. And, in the third chapter, correlations between reproductive success and hybridization were investigated in a wild population, as well as the genomic and ecological mechanisms responsible for those changes. The first chapter of this dissertation aimed to identify how traits potentially involved in fitness (embryonic survival, ova size, ova energy concentration, sperm motility, burst swimming performance, juvenile survival, and juvenile growth) changed with hybridization between cutthroat and rainbow trout and whether those changes could explain previously observed reductions in reproductive success of individuals with increased rainbow trout ancestry. Using progeny from wild caught fish, differences in phenotypes based on hybridization were observed for embryonic survival, ova energy concentration, juvenile weight, and burst swimming based on ancestry. However, the correlations differed from previously observed patterns of reproductive success and likely do not explain declines in reproductive success associated with hybridization. The second chapter of this dissertation aimed to identify how hybridization affects the genome by identifying genomic regions with changes in recombination rates in the hybrid relative to rainbow trout as well as genomic areas with excess species-specific ancestry in the hybrid. Previous studies of hybridization have observed recombination suppression in genomic regions where structural differences, such as inversions or karyotype differences, exist between parental species. Such regions may retain groups of adaptive alleles. Additionally, adaptive divergence between the parental species may result in alleles that are preferentially selected in the hybrid progeny. Identification of regions with suppressed recombination or excess species-specific ancestry would provide insight into markers that may be important to fitness and that have differentially evolved in each of the parental species. In total, eight and seven chromosomes were identified to have changes in recombination rates in the hybrid female and male relative to O. mykiss. Recombination was suppressed in the hybrids on two chromosomes with known structural differences between the parental species. In addition, changes in recombination rates were observed on five chromosomes with high proportions of duplicated markers and may be due to increased homeologous chromosome pairing. Recombination patterns were similar between the sexes which suggests that hybridization affects recombination in the same way in females and males. Regions of excess species-specific ancestry covered 11 and 10% of the mapped genome in the female and male and regions of excess were evenly split between cutthroat trout and O. mykiss. Genetic drift may be responsible for much of the observed patterns of excess species-specific ancestry, but selection may also play a role. The aim of the third chapter of this dissertation was to identify the fitness consequences of hybridization, mechanisms responsible for the retention of hybridization, and genomic regions correlated with changes in reproductive success in a wild population of westslope cutthroat trout hybridized with non-native rainbow trout. Adult samples from a previous study, collected over a five year period, were sequenced at 3027 loci. Increased admixture from non-native rainbow trout had a strong, negative effect on reproductive success. A decline of 53% was observed for individuals with an increased genetic contribution of 0.20 from rainbow trout. Despite apparent strong selection against rainbow trout ancestry, hybridization appears to be maintained largely by the invasion of rainbow trout from outside populations as well as the relatively high fitness of few hybrid individuals. Ten loci correlated with reproductive success were identified in females. Seven of the ten loci were linked to chromosomes and three were positioned on chromosomes. Loci linked to reproductive success were identified on chromosomes with excess species-specific ancestry in hybrid progeny (RYHyb14 and RYHyb18) as well as chromosomes with a high proportion of duplicated markers (RYHyb02) and known Robertsonian polymorphism (RYHyb20). The research presented in this dissertation will elucidate our understanding of the phenotypic and genetic changes correlated with hybridization between rainbow and cutthroat trout as well as identify genetic and ecological mechanisms that may be responsible for those changes. In addition, results from this study provide insight into differences in adaptive divergence and markers that may be involved in the early stages of speciation in the wild. Results could be used by managers to identify populations that are at risk from hybridization.
Author: Matthew C. Boyer Publisher: ISBN: Category : Cutthroat trout Languages : en Pages : 12
Book Description
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 (?ST = 0.076, ?ST = 0.094, P
Author: Carl O. Ostberg Publisher: ISBN: Category : Languages : en Pages : 157
Book Description
Introgressive hybridization creates novel gene combinations that may generate important evolutionary novelty and thus contribute to biological complexity and diversification. On the other hand, hybridization with introduced species can threaten native species, such as cutthroat trout (Oncorhynchus clarkii) following the introduction of rainbow trout (O. mykiss). While rainbow trout introgression in cutthroat trout is well documented, neither the evolutionary consequences nor conservation implications are well understood. Hybridization between rainbow and cutthroat trout occurs in the context of substantial chromosomal rearrangement, as well incompletely re-diploidized genomes. Rainbow and cutthroat trout are descended from an autopolyploid ancestor, and extensive chromosome arm rearrangements have occurred between the species following their divergence from the last common ancestor. Evidence for incomplete re-diploidization includes the occasional formation of multivalents and duplicated loci occasionally exhibit a mixture of disomic and tetrasomic inheritance. Thus, transmission genetics may be complicated by recombination between homeologs. Here, I evaluated the phenotypic and genetic consequences of introgression between rainbow trout and Yellowstone cutthroat trout (O. clarkii bouvieri) to provide insights into genome processes that may help explain how introgression affects hybrid genome evolution. The overall aim of the first part of this dissertation (Chapters 1 and 2) was to evaluate phenotypic variation and gene expression among parental species and hybrids to gain insight into the genetic basis of hybrid and parental morphologies. We constructed seven line crosses: both parental species, both reciprocal F1 hybrids, first-generation backcrosses, and F2 hybrids. In Chapter 1, we aimed to assess the role of introgression on growth (length and weight gain), morphology, and developmental instability among these seven crosses. Growth was related to the proportion of rainbow trout genome contained within crosses. Rainbow and cutthroat trout were morphologically divergent: rainbow trout were generally robust whereas cutthroat trout were typically more slender and their hybrids tended to be morphologically intermediate, although backcrosses were morphologically more similar to their backcrossing parental species. These differences in growth and body morphology may be maintained, in part, through the regulation of muscle growth-related genes. Therefore, in Chapter 2, we aimed to characterize the expression of muscle growth-related genes and to describe relationships between gene expression and growth patterns among parental species and hybrids to gain insight into the underlying genetic basis of the difference in their body shapes. Our findings suggest that rainbow and cutthroat trout exhibit differences in muscle growth regulation, that transcriptional networks may be modified by hybridization, and that hybridization disrupts intrinsic relationships between gene expression and growth patterns that may be functionally important for phenotypic adaptations. The overall aim of the second part of this dissertation (Chapters 3 and 4) was to assess the genetic consequences of introgression to determine how the genomic architecture of hybrids affects allelic inheritance, and thus their subsequent evolution. In Chapter 3, we generated a genetic linkage map for rainbow-Yellowstone cutthroat trout hybrids to evaluate genome process that may influence introgression genome evolution in hybrid populations. Our results suggest that few genomic incompatibilities exist between rainbow and cutthroat trout, allowing their to genomes introgress freely, with the exception that differences in chromosome arrangement between the species may act as barriers to introgression and enable large portions of non-recombined chromosomes to persist within admixed populations. In Chapter 4, we aimed to determine the effect of incomplete re-diploidization on transmission genetics in hybrids, compared to pure species. We used the parental gametic phase from existing genetic linkage maps to identify the homeologs that recombine, to characterize this recombination, and to verify meiotic models of residual tetrasomic inheritance in autotetraploids. Recombination between homeologs occurred frequently in hybrids and results in the non-random segregation of alleles across extended chromosomal regions as well as extensive double-reduction in hybrid parental gametes. Taken together, the results from Chapters 3 and 4 suggested that chromosome rearrangements and recombination of homeologs could influence genome evolution in admixed populations. The research presented in this dissertation indicated that the evolutionary fate of hybrid genomes is unpredictable. Some of our findings suggest that introgressions proceeds in a predictable fashion in admixed populations; rainbow and cutthroat genomes freely introgress, with the exception that chromosome rearrangements may suppress recombination across large chromosomal regions. However, homeologous recombination during meiosis in hybrids results in unpredictable segregation of chromosomes, and the segregation of these chromosomes may depend on the hybrid generation of each parent within an admixed population. Furthermore, phenotype and gene expression are quantitative traits, and expression of these traits may depend on hybrid genotypes across transcriptional networks that are controlled by genes distributed over the entire genome. Consequently, hybridization may alter transcriptional regulation of genes, resulting in unpredictable gene expression patterns, which, in turn, contribute to the high phenotypic variation in hybrids.
Author: M. M. Yau Publisher: ISBN: Category : Cutthroat trout Languages : en Pages : 8
Book Description
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
Author: Clint Cain Muhlfeld
Author: Clint Cain Muhlfeld
Author: Matthew Corsi
Author: Daniel P. Drinan
Author: Michael D. Robinson
Author: 
Author: Matthew C. Boyer
Author: Carl O. Ostberg
Author: M. M. Yau
Author: Michael Patrick Peterson
Author: Nathaniel P. Hitt