Song divergence and male dispersal among bird populations: a spatially explicit model testing the role of vocal learning.

The importance of bird song in sexual selection and the widespread existence of geographical variation in song has raised the question of whether dialects can promote the evolution of new, reproductively isolated, subgroups. However, the effect of song learning on the relation between song divergence and gene flow is still poorly understood. We explored the origin and maintenance of song divergence and its consequences for male dispersal between populations. To do this, we used a spatially explicit model to study the effect of vocal learning mode (predispersal and postdispersal) and the role of intrasexual selection among males. The majority of scenarios simulated in the model led to significant genetic and phenotypic song divergence, consistent with the widespread occurrence of dialects in natural populations. Intrasexual selection in the form of male exclusion, dependent on song matching between neighbours, was an efficient mechanism driving song divergence. Most importantly, song learning was decisive in causing an incongruence of genetic divergence and song divergence between populations. As a consequence, song learning often prevented the expected negative relation between the degree of song divergence and dispersal. These findings may help to interpret empirical data on song divergence and gene flow and provide qualitative and testable predictions for conditions under which intraspecific song variation may promote reproductive divergence and speciation. © 2003 Published by Elsevier Science Ltd. on behalf of The Association for the Study of Animal Behaviour.