Date of Award


Publication Type

Master Thesis

Degree Name



Biological Sciences


Biology, Molecular.


Heath, D.




Sympatric coastal cutthroat trout (Oncorhynchus clarki clarki ) and coastal rainbow/steelhead trout (O. mykiss irideus ) are thought to be reproductively isolated primarily by spatial and temporal separation. However, interspecific hybridization has been documented, thus raising the questions of how widespread hybridization is within their native range, and what are the nature and status of reproductive isolating mechanisms (i.e. prezygotic or postzygotic) in the hybridizing sympatric populations? In a broad survey of 37 populations on Vancouver Island, hybridization between these trout species was found to be widespread (Chapter 2). The frequency of hybridization varied among locations (HI = 3%--88%; II = 2%--54%), with some populations displaying hybrid levels indicative of hybrid swarms and may be undergoing 'hybrid meltdown'. Several environmental factors appear to influence hybridization (e.g. forest harvesting, stocking, habitat availability, watershed size), however, no single factor appears to have a dominant effect. There is no consistent evidence for selection acting against first-generation (F1) hybrids, and in backcross hybrids inconsistent results implicate environment-dependent (i.e. extrinsic) selection (Chapter 3). Hybridization is reciprocal, but nuclear marker patterns show that the direction of hybridization is unidirectional in some populations (n = 5 out of 13 populations). Based on cytonuclear disequilibrium levels, a remarkable reproductive bias appears to exist (i.e. frequency of backcross hybrids with matched nuclear-mitochondrial marker composition exceeded mismatched genotypes). Selection against mismatch genotypes may be occurring, although a behavioural mating bias is more likely.Dept. of Biological Sciences. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2004 .B44. Source: Masters Abstracts International, Volume: 43-01, page: 0157. Adviser: Daniel Heath. Thesis (M.Sc.)--University of Windsor (Canada), 2004.