recombination & sex
Agrawal AF 2009 Differences between selection on sex versus recombination in Red Queen models with diploid hosts. Evolution 63:2131-2141.
- sex and recombination are not equivalent in diploids because selection on sex depends on the consequences of segregation as well as recombination
- recombination breaks down associations between genes on the same chromosome whereas segregation destroys associations between genes on homologous chromosomes
- parasites tend to select against both sex and recombination
- though recombination is favored more often than is sex
- there is little correspondence between the conditions favoring sex and those favoring recombination
- indicating that the direction of selection on sex is often determined by the effects of segregation, not recombination
- in many real systems, parasites have faster generation times than their hosts
- this can be modeled in a variety of ways
- the approach used here is to scale time with respect to parasite generations and assume that the frequency of host genotype i after one complete parasite generation is Hi[t + 1] = (1 − 1 / n) Hi[t] + (1 / n) Hi''[t], where n is the number of parasite generations per host generation
- equivalent to assuming that a fraction (1 - 1 / n) of hosts is in some form of stasis (e.g., seed bank) and the remainder proceeds through the life cycle at the same rate as the parasites
- this may not be the most realistic way to model differences in generation times
- it should capture the essence of the problem
- the number of parasite generations per host generation, n, had little effect on the evolution of either sex or recombination modifiers
- this observation contrasts sharply with the results reported by Salathé et al. (2008b)
- who found that reducing parasite generation time (increasing n) dramatically increased selection for genetic mixing
- the discrepancy with respect to the effect of parasite generation time is likely due to differences in how the life cycle is modeled
