Amazon molly (Poecilia formosa) females reproduce asexually, but they
need sperm to initiate the process. Such gynogenetic reproduction can be called sperm
parasitism since the DNA in the sperm is not used. Since all offspring of asexually
reproducing females are females, they can locally outcompete sexually reproducing ones,
but their persistence is threatened by the lack of males. Therefore, the existence of
Amazon mollies is puzzling. A metapopulation structure has been suggested to enable the
coexistence of gynogenetic and sexual species. Previously only Levins-type metapopulation
models have been used to investigate this question, but they are not defined on the
individual level. Therefore we investigate the evolution of sperm parasitism in a
structured metapopulation model, which incorporates both realistic local population
dynamics and individual-level dispersal. If the reproduction strategy is freely evolving
in a large well-mixed population or in the structured metapopulation model, strong
discrimination of asexually reproducing females by males results in evolution to full
sexuality, whereas mild discrimination leads to too small probability of sexual
reproduction, so that the lack of males causes the extinction of the evolving population,
resulting in evolutionary suicide. This classification remains the same also when both
sexual reproduction and dispersal are freely evolving. Sexual and asexual behaviour can be
observed at the same time in this model in the presence of a trade-off between the
reproduction and dispersal traits. However, we do not observe disruptive selection
resulting in the evolutionarily stable coexistence of fully sexual and fully asexual
females. Instead, the presence of sexual and asexual behaviour is due to females with a
mixed reproduction trait.