Acoustic innovations in courtship sounds generated by hybridization in cichlid fish

Abstract

Abstract During courtship, prezygotic barriers are thought to maintain the diversity of species since differences in phenotypic traits and reproductive behaviours are likely to be involved in maintaining species boundaries. However, introgressive hybridization has been reported in many different taxa and the resulting hybrids usually possess phenotypic features, including behaviours, that are intermediate between those of the parents. The outcome of hybrids may depend on the interactions between the intrinsic viability of the hybrids, the ecological environment of the species, and the fitness of hybrids in that ecological context. In cichlids, the mechanism of hybridization is increasingly documented as an important factor in their evolutionary radiation since it may provide novel gene combinations that promote speciation and adaptive radiation by generating new transgressive phenotypes. Cichlid species are separated mostly by pre-mating isolating mechanisms. Like colour patterns, acoustic communication is involved in sexual selection, but this pattern has been much less studied and the outcome of hybridization on acoustic features has never been examined. To gain novel insights into the evolution of their acoustic communication behaviour, we performed a hybrid cross between Chindongo saulosi and Maylandia estherae. Qualitative examination of courtship showed that the three groups possess the same sequence of behaviours. However, sounds produced during courtship showed specific signatures since all three groups differ at the level of sound duration and pulse period, with both features being intermediate in hybrids in comparison to the two parent species. Colour patterns in hybrids were also different from those of the parent species. These results show that hybridization can affect at least two kinds of prezygotic barriers, which may be important in the cichlid evolutionary process. However, playback experiments are required to test the strength of these features in sexual selection.