In estuaries throughout the northern hemisphere resident-freshwater forms of the threespined stickleback <i>(Gasterosteus aculeatus) </i>have undergone parallel divergence from their marine ancestors. Sticklebacks are useful for studies of reproductive isolation and speciation because divergent resident-freshwater and migratory anadromous forms exist in sympatry in the lower reaches of rivers. A great deal is already known about the evolutionary history of sticklebacks, however, little is known about reproductive isolation in wild populations. In this thesis, I investigate the nature of reproductive isolation in an anadromous-freshwater stickleback hybrid zone located in the River Tyne, Scotland and explore whether the same genes underlie variation in the same traits in different populations. 1. There was no evidence of morphotype-based assortative mating, in an experimental pond manipulation. Hybridisation between morphotypes occurred readily and this in part is due to the tendency of freshwater females to mate with large males. 2. In contrast, there is some evidence of premating isolation existing in the River Tyne wild population, and this is likely to be ecologically dependent assortative mating. Premating isolation is not strong, however, since hybrid juveniles represented 33% of the sample from sympatric sites. There was no evidence of hybridisation showing a directional bias. 3. Evidence suggests that morphological and genetic differences between anadromous and freshwater sticklebacks in the River Tyne are maintained by postmating isolation in the wild. Genetic hybrids had reduced probability of overwinter survival. There is also strong evidence for selection against intermediate morphotypes and this selection may be sex-biased against intermediate lateral plate morphs. 4. Statistical associations between loci and traits were detected and suggest both stability and flexibility in the underlying morphological divergence in sticklebacks.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:653144 |
| Date | January 2005 |
| Creators | Jones, Felicity C. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/15117 |
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