Signal evolution in the bushcricket Mecopoda elongata

The "Mecopoda elongata"-group comprises a number of cryptic species of katydids (Orthoptera; Tettigoniidae), where most species cannot be distinguished by morphology, but show striking differences in the temporal pattern of male calling songs. Within this group the most conspicuous difference in the various song types is that between a very regular chirp pattern on the one hand (with different chirp periods and chirp durations), and more or less continuous trills on the other hand. Both chirping and trilling species are found in Malaysia, Thailand, Sulawesi and two locations in India; In this project, we plan to test whether chirping and trilling song types evolved independently several times. We will first investigate whether groupings based on the similarity of song temporal patterns correspond with genetic groupings, using AFLP data to estimate genetic relationships. Female choice experiments will determine the strength of female preferences for conspecific and heterospecific male song, and thus test whether genetic boundaries are maintained by female preference for their own song type. Insects often call in mixed choruses of considerable numbers of species and individuals. Sympatric species may exhibit a stronger discrimination for mating signals than allopatric species. Whereas the song types of M. elongata differ substantially in temporal pattern, they are almost identical in frequency composition, with the consequence of strong masking interference. Therefore, we expect receiver selectivity for temporal patterns to be stronger in sympatric females. To identify patterns of character displacement, we will test whether allopatric females are less discriminating than sympatric ones. In addition, components of male behaviour, such as choice of calling sites, signalling time and signal structure, will be compared in sympatry and in allopatry. Tettigoniidae exhibit variable chromosome numbers ranging from 2n=12 (neo XY) to 2n=37 (XO), with considerable differences within genera. Although it is likely that fixed karyotype differences between closely related species are a consequence, rather than the cause, of genetic isolation, we consider the question whether divergence in karyotype acts as a postmating isolation mechanism and investigate, whether geographic, phylogenetic or song differences are accompanied by different chromosome numbers.

The "Mecopoda elongata"-group comprises a number of cryptic species of katydids (Orthoptera; Tettigoniidae), where most species cannot be distinguished by morphology, but show striking differences in the temporal pattern of male calling songs. Within this group the most conspicuous difference in the various song types is that between a very regular chirp pattern on the one hand (with different chirp periods and chirp durations), and more or less continuous trills on the other hand. Both chirping and trilling species are found in Malaysia, Thailand, Sulawesi and two locations in India; In this project, we plan to test whether chirping and trilling song types evolved independently several times. We will first investigate whether groupings based on the similarity of song temporal patterns correspond with genetic groupings, using AFLP data to estimate genetic relationships. Female choice experiments will determine the strength of female preferences for conspecific and heterospecific male song, and thus test whether genetic boundaries are maintained by female preference for their own song type. Insects often call in mixed choruses of considerable numbers of species and individuals. Sympatric species may exhibit a stronger discrimination for mating signals than allopatric species. Whereas the song types of M. elongata differ substantially in temporal pattern, they are almost identical in frequency composition, with the consequence of strong masking interference. Therefore, we expect receiver selectivity for temporal patterns to be stronger in sympatric females. To identify patterns of character displacement, we will test whether allopatric females are less discriminating than sympatric ones. In addition, components of male behaviour, such as choice of calling sites, signalling time and signal structure, will be compared in sympatry and in allopatry. Tettigoniidae exhibit variable chromosome numbers ranging from 2n=12 (neo XY) to 2n=37 (XO), with considerable differences within genera. Although it is likely that fixed karyotype differences between closely related species are a consequence, rather than the cause, of genetic isolation, we consider the question whether divergence in karyotype acts as a postmating isolation mechanism and investigate, whether geographic, phylogenetic or song differences are accompanied by different chromosome numbers.