Group tolerance, dispersal evolution, and the maintenance of polymorphism in recognition cues

In some systems, organisms form or join groups mediated by certain recognition cues. However, it is predicted that variability in such cues cannot be maintained as positive, frequency-dependent selection favors the dominant cue (Crozier's paradox). We utilize a simple analytical model of 2 groups as well as computer simulations to find conditions where the coexistence (polymorphism) of 2 distinct recognition cues is maintained. We assume a species that forms reproductive groups and the adoption of a newborn individual into a group depends on that individual's genotype (recognition cue) in relation to the group's profile. We investigate the role of 2 factors affecting the level of isolation between groups, namely group tolerance toward deviant genotypes and dispersal between groups. Results from the analytical model show that high tolerance or high dispersal lead to the global fixation of a single genotype, whereas low group tolerance and low dispersal promote the globally stable coexistence of different genotypes. Interestingly, coexistence can only be global, with a different genotype dominating each group, or local, with 2 genotypes coexisting in one group, depending on the degree of tolerance and dispersal. Local coexistence, however, does not persist, when dispersal is allowed to evolve. In this case, low dispersal evolves, which stabilizes global coexistence but reduces local coexistence. If we expand the number of groups and assume spatially limited dispersal, global coexistence becomes a more likely outcome even under conditions where it was impossible in the 2-group system.