Geissmann, T. 1984: Duet splitting and the evolution of gibbon (Hylobates spp.) song. Antropologia Contemporanea 7 (2): 158 (Abstract only).
Anthropological Institute, University Zürich-Irchel
Long and complex song bouts have been described for all gibbon species. Comparison of their singing behaviour indicates that:
1. The recent hylobatids represent a monophyletic group whose common ancestor produced duet songs, although not all recent species are known to do so.
2. The duet patterns of the various species can be linearly arranged in stages of increasing song splitting between the partners. This hypothetical evolutionary route has previously been introduced to illustrate the evolution of duet singing in some bird species. Duet songs of recent gibbon species are likely to have evolved according to this song splitting theory.
3. Not all recent hylobatids are known to engage in duet songs. Evidence is presented as to why this is not considered to be a primitive trait, but rather an advanced and apomorph evolutionary stage, not yet contained in the song splitting theory.
In the evolution of gibbon songs, a process tentatively called "duett splitting" is suggested to have secondarily led from a dueting species to a non-dueting species, in that the contributions of the pair partners split into temporally segregated solo songs.
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