Geissmann, T. 2000: Duet-splitting in the evolution of gibbon songs - Duet-Splitting in der Evolution von Gibbon-Gesängen. Folia Primatologica 71: 194 (Abstract only).

Duet-splitting in the evolution of gibbon songs - Duet-Splitting in der Evolution von Gibbon-Gesängen

T. Geissmann

Institute of Zoology, Tieraerztliche Hochschule Hannover

All species of gibbons are known to produce elaborate, species-specific and sex-specific patterns of vocalisation usually referred to as "songs". In most species, mated pairs may characteristically combine their songs in a relatively rigid pattern to produce coordinated duet songs. Previous studies disagreed on whether duetting or the absence of duetting represented the primitive condition in gibbons.

This study compares singing behaviour in all gibbon species. Various vocal characteristics were subjected to a phylogenetic analysis using previously published phylogenetic trees of the gibbon radiation as a framework. Variables included the degree of sex-specificity of the vocal repertoire, the occurrence of solo songs, and the preference for a specific daytime for song-production. The results suggest the following scenario for the evolution of gibbon songs:

1. The last common ancestor of recent gibbons produced duet songs.
2. Gibbon duets probably evolved from a song which was common to both sexes and which only later became separated into male-specific and female-specific parts (song-splitting theory).
3. A process tentatively called "duet-splitting" is suggested to have secondarily led from a duetting species to a non-duetting species, in that the contributions of the pair-partners split into temporally segregated solo-songs.