Segregation distortion in a deme structured population: opposing demands of gene, individual and group selection

The evolution of segregation distortion is governed by the interplay of sel ection at different levels. Despite their systematic advantage at the gamet e level, none of the well-known segregation distorters spreads to fixation since they induce severe negative fitness effects at the individual level. In a deme-structured population, selection at the population level also pla ys a role. By means of a population genetical model, we analyse the various factors that determine the success of a segregation distorter in a metapop ulation, Our focus is on the question of how the success of a distorter all ele is affected by its segregation ratio and its fitness effects at the ind ividual level. The analysis reveals that distorter alleles with high segreg ation ratios are the best invaders and reach the highest frequencies within single demes. However, the productivity of a deme harbouring a distorter w ith a high segregation ratio may be significantly reduced. As a consequence , an efficient distorter will be underrepresented in the migrant pool and, moreover, it may increase the probability of deme extinction. In other word s, efficient distorters with high segregation ratios may well succumb to th eir own success. Therefore, distorters with intermediate segregation ratios may reach the highest frequency in the metapopulation as a result of the o pposing forces of gamete, individual and group selection. We discuss the im plications of this conclusion for the t complex of the house mouse.