Date of Award:

5-1-1995

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Department name when degree awarded

Biology

Committee Chair(s)

Kimberly A. Sullivan

Committee

Kimberly A. Sullivan

Committee

Paul G. Wolf

Committee

Jeffery L. Kershner

Abstract

Fishes of the western United States, in particular native salmonids, are at risk of extinction as a result of human activities. One major threat to native fishes is hybridization with exotic species introduced by humans. Enzyme electrophoresis was used to determine the degree of hybridization between native Colorado River cutthroat trout (Oncorhynchus clarki pleuriticus) and introduced rainbow trout (Oncorhynchus mykiss) in ten streams located across five drainages on the north slope of the Uinta Mountains in Utah, USA. To assess the level of hybridization in each individual, I constructed a hybrid index using 10 diagnostic loci that differed between Colorado River cutthroat trout and rainbow trout. Of the 190 fish sampled, I classified 172 as cutthroat trout, 18 as hybrids, and zero as rainbow trout using 10 diagnostic loci. Hybrid individuals were identified in 8 of the 10 streams sampled. Genetic and morphological analyses supported the conclusion that hybridization has occurred in the past, but little hybridization is occurring at present. Hierarchial F-statistics indicated considerable differentiation between sample points within streams, no additional differentiation at the stream to watershed level, and moderate additional differentiation at the watershed to total level. Observed average heterozygosity was 0.059 and the proportion of polymorphic loci averaged 18.3. A genetically effective population size was estimated for one drainage and one stream with low levels of hybridization. West Fork Smith Fork and East Fork of Blacks Fork had effective population sizes of 80.7 and 15.3, respectively. The genetic variation within the streams suggests that the past hybridization may have homogenized the gene pool of this population of Colorado River cutthroat trout.

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