Evolution of specialisation in sexual and asexual organisms

In a variable environment, producing genetically variable offspring, such as sexual organisms do, may have different consequences than producing genetically identical offspring, such as asexual organisms do. Theoretical work has coined the concept of general-purpose genotype: asexual clones that survive for many generations will be tolerant to a variety of environmental conditions. Another concept is the Frozen Niche Variation model: in a spatially heterogeneous environment, asexual specialists can easily invade a sexual population if the individual organisms can choose their favourite niche. So, these ideas have different expectations about the degree of specialism asexual organisms should have, though how this relates to the degree of specialism in sexual organisms is not entirely clear. In the natural world, the environmental variation may comprise both temporal and spatial components. Also, many organisms do not find their own niche, as is assumed by the Frozen Niche Variation model, but disperse a certain distance from their parents. This paper describes the results of a simulation model. It studies the evolution of specialism and generalism in sexually and asexually reproducing organisms under different patterns of environmental variation in both space and time. The results show that general- purpose genotypes will evolve in a fluctuating environment in sexuals as well as asexuals if population sizes are small, so genetic variation gets depleted in the sexuals. In a spatially structured environment with limited dispersal, many specialist genotypes can co-exist, and under restricted conditions the optimal asexual genotype may be more specialist than the optimal sexual genotype. Some consequences of environmental variation in both space and time are shown, as well as some effects of interaction between sexuals and asexuals.