Human introductions of exotic species are a major factor in the decline and extinction of native species. Fish species have been extensively introduced beyond their native ranges in the United States often intentionally as recreation and food resources. Cutthroat trout (Oncorhynchus clarkii) are an economically, politically, and ecologically valuable species of fish in the Western United States that have suffered precipitous declines since European settlement. This polytypic species is divided into 14 subspecies of which 2 are extinct, 3 are federally listed under the Endangered Species Act, and most have state protection.
I examined the pattern of hybridization between introduced rainbow trout (O. mykiss) and native greenback cutthroat trout in two Colorado streams using mitochondrial DNA and multiple nuclear gene markers. I found evidence that mitochondrial DNA introgression in hybrids is asymmetric and more likely from rainbow trout than from greenback cutthroat trout. Additionally, the presence of intra-specific cytonuclear associations found in both populations is concordant with current hypotheses regarding co-evolution of mitochondrial and nuclear genomes. The observation of significant departures of genotype frequencies from the expectations of a hybrid swarm suggest that these populations have intrinsic value for understanding the evolution of trout, information that may turn out to be relevant for implementing effective long-term conservation strategies.
Accurate assessment of species identity is fundamental for conservation biology. Using molecular markers from the mitochondrial and nuclear genomes, I discovered that many putatively native populations of greenback cutthroat trout were the non-native Colorado River cutthroat trout (O. c. pleuriticus ), which is native to the Colorado River basin. The error can be explained by the introduction of Colorado River cutthroat trout throughout the native range of greenback cutthroat trout in the late 19th and early 20th centuries by fish stocking activities. Unfortunately, my results suggest that greenback cutthroat trout within its native range is at a higher risk of extinction than previously thought, despite conservation activities spanning more than two decades.
Fish stocking activities not only compromised the conservation management of greenback cutthroat trout, but also obscured its evolutionary history. The presence of non-native Colorado River cutthroat trout in the native range of greenback cutthroat trout led researchers to erroneously conclude that the two subspecies only diverged at the end of the Pleistocene about 10,000 years ago. I demonstrate that greenback cutthroat trout have a unique evolutionary history comprising at least 500,000 years. Furthermore, greenback cutthroat trout share a complex evolutionary history with Rio Grande cutthroat trout. Genetic data reveal that greenback cutthroat trout may have been established by at least two invasions from the Rio Grande, Pecos, or Canadian drainages.
|Advisor:||Martin, Andrew P.|
|Commitee:||Collinge, Sharon, Guralnick, Robert, Stock, David|
|School:||University of Colorado at Boulder|
|Department:||Ecology and Evolutionary Biology|
|School Location:||United States -- Colorado|
|Source:||DAI-B 68/07, Dissertation Abstracts International|
|Subjects:||Molecular biology, Genetics|
|Keywords:||Conservation genetics, Greenback cutthroat trout, Oncorhynchus clarkii stomias|
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