The evolution of release and advertisement calls in green toads (Bufo viridis complex)

In the present paper we tested the hypothesis that differences in the acoustic communication system of diploid and tetraploid green toads (Bufo viridis complex) might be due to selection for reproductive character displacement. We recorded two acoustic signals of the toad repertoire − the advertisement call (a long range mate-attracting signal) and the release call (a short-range signal mediating male–male interactions) − from six sympatric Central Asian populations (three diploid and three tetraploid populations) as well as from three allopatric diploid populations from Italy, and compared their patterns of variation with the pattern of among-population genetic distances. Although release and advertisement calls share the same morpho-physiological constraints, they show significantly different patterns of variation. Release calls vary congruently with the pattern of genetic distances, suggesting that mutation and genetic drift have been the major forces responsible for their change both in time and space. By contrast, the pattern of advertisement-call variation is not consistent with the phylogeny of the group, because the advertisement calls of Asian diploid and tetraploid populations differ from each other more than their genetic distances would predict. These results strongly support the hypothesis that selection acted on the advertisement calls of either or both Asian taxa, possibly, to favour reproductive isolation. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 77, 379–391.