The evolution of sex‐biased dispersal by pre‐dispersal copulation and fluctuating environment

Abstract

Summary 1.Additional factors relevant to dispersal are necessary to establish a general theory that can explain the sex-biased dispersal pattern of most taxa. The present study evaluated the influence of pre-dispersal copulation on the evolution of sex-biased dispersal. The influence of fluctuating environment, population size and dispersal cost were also analysed. 2. The simulation models were designed on the basis of the life history of Pieris rapae crucivora , in which female butterflies disperse among local habitats after copulation although male butterflies remain in the natal habitat. In the first model, where females always copulate before dispersal, the evolution of female-biased dispersal was facilitated by the fluctuating environment, but was suppressed by the stable environment. However, the fluctuating environment also suppressed the sex-biased dispersal in the second model where female dispersers always copulate after dispersal. Thus, the interaction between the pre-dispersal copulation and the fluctuating environment is a sufficient condition for the evolution of sex-biased dispersal. 3. The present study is the first report to reveal the important influence of pre-dispersal copulation on the evolution of sex-biased dispersal. In addition, the sexual difference in dispersal pattern increased with the increase of local population size and the decrease of dispersal cost.

The evolution of sexual difference in dispersal strategy sensitive to population density

“…The early dispersal of females evolved in the current models assuming that individuals regulate dispersal timing according to the conditions of local populations, as observed in previous models that do not assume such a plastic phenotype (Hirota, 2004(Hirota, , 2005; however, the resultant dispersal timing is different among the previous and current models. This difference is caused by phenotype plasticity which realizes an adaptive dispersal pattern according to local conditions, and the sexual difference in essential factors affecting reproductive success.…”

“…Individual life history is shown in Fig. 1 and is based roughly on the life history of herbivorous insects (Hirota, 2004). Each component of the life history is accounted for as follows.…”

“…In previous models which assumed that dispersal timing is determined solely by genetic factors (Hirota, 2004(Hirota, , 2005, individuals could not respond immediately to temporal changes of local population density. In those models, maladaptive dispersal behaviors are often observed in a fluctuating environment, although the selected genetic traits are adaptive in the long term.…”

“…Previous models (Hirota, 2004(Hirota, , 2005 demonstrated that pre-dispersal copulation facilitated the evolution of female-biased dispersal under the fluctuating environment. Females should migrate and reproduce over habitats to spread their risk due to environmental fluctuation.…”

“…Several theoretical studies have discussed the evolutionary process of sex-biased dispersal (Gandon, 1999;Perrin and Mazalov, 2000;Hirota, 2004); however, those models assumed that the dispersal rate and timing was determined completely by genes and ignored the phenotype plasticity sensitive to fluctuating conditions of the natal habitat. In the present study, therefore, previous models (Hirota, 2004(Hirota, , 2005 were thoroughly modified to evaluate whether sex-biased dispersal evolves, even when the dispersal pattern is determined not solely by genes but by the interaction of genetic factors with local population density.…”