Geographic variation in acoustic communication: reproductive character displacement and speciation

Background: Reproductive character displacement is a geographical pattern in which mate-attracting signals, preferences or both differ more in areas of sympatry than in areas of allopatry. Questions: What selective forces drive reproductive character displacement? What are its consequences? Methods: Reproductive character displacement in mate-attracting signals and/or female preferences are described for pairs of closely related field crickets (Gryllus), periodical cicadas (Magicicada), chorus and treefrogs (Pseudacris and Hyla), and tinkerbirds (Pogoniulus). These examples were characterized by data from multiple populations and evidence regarding the efficacy of sympatric divergence in signals or preferences. Conclusions: Whereas selection resulted in changes that reduce the production of genetically or behaviourally unfit hybrids in field crickets, chorus frogs, and green and grey treefrogs, reproductive character displacement in periodical cicadas and tinkerbirds was most likely driven by masking interference or mistakes in the identification of territorial rivals. Reproductive character displacement may not only accentuate or preserve divergence that arises in allopatry but can result in cascades of speciation if assortative mating arises between displaced and non-displaced populations