Fig. 1

The outcome of competition between a genetically diverse sexual population and a single asexual genotype. The results are based on computer simulations wherein a clone is introduced by mutation into a sexual population at generation 1000. a No parasite. In the absence of parasites, the clone rapidly eliminates the sexual population. The asexual clone also reaches a higher carrying capacity, because asexual females can replace themselves on fewer resources (see Lively 2009). b Virulent parasites present. Here, the clone increases after its introduction, driving the sexual population down; but parasites quickly evolve to infect the clone and drive it to extinction. The sexual population then increases to its previous density. c Virulent parasites present. Here, the clone invades the sexual population, and is subsequently driven down in frequency by parasites, but it does not go extinct. The clone then begins to oscillate in the population. Nonetheless, the parasites have prevented the clone from driving the sexual population to extinction. The simulation is described in Lively (2009). In b and c, infected females produce one offspring, while uninfected females produce three offspring