The effects of spatial structure are explored using a simple model of migration between two populations, each in a balance between mutation and stabilising selection on an additive polygenic trait. Gene flow can maintain genetic variance within each population, albeit at low levels. If the optimum fluctuates in time, much higher levels of genetic variation can be maintained within populations, and in the presence of isolation divergence between the populations can be seen. Biotic interactions may be an important factor maintaining variation within and between populations, and these may lead to Red Queen dynamics even in constant environments. Here I define the Red Queen very broadly as "ongoing coevolution", and discuss the use of the terms 'coevolution' and 'ongoing'. I suggest that different Red Queen type processes can be classified the amount of novelty available in the system and by whether or not increasing sophistication occurs. In this thesis I model a specific biotic interaction: the coevolution of parasites with the acquired immunity of their hosts. High levels of linkage disequilibrium (strain structure) can be maintained in this system, and for a large range of parameters Red Queen type dynamics are observed. In some cases fluctuations in linkage disequilibrium and epistasis may result in a fairly large advantage to sexual over asexual recombination. However, this advantage is not large enough to outweigh the "two-fold cost of sex". This deterministic advantage arises primarily because recombination impedes the response to fluctuating epistasis rather than because it facilitates the response to directional selection. Sex may also be advantageous in the presence of Red Queen type dynamics because sexual genotypes that are stochastically lost can be recreated through recombination, unlike their asexual counterparts.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:654154 |
| Date | January 1999 |
| Creators | Lythgoe, Katrina Abigail |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/15240 |
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