Evolution of Communication in Gibbons (Hylobatidae) Inaugural-Dissertation zur Erlangung der philosophlschen DoktorwOrde vorgelegt der Philosophischen Fakultat II der Universitat Zurich von THOMAS GEISSMANN von Hagglingen Begutachtet von den Herren Prof. Dr. R.D. Martin Dr. D.J. Chivers Zurich 1993 Zentralstelle der Studentenschaft Evolution of Communication in Gibbons (Hylobatidae) Inaugural-Dissertation zur Erlangung der philosophischen Doktorwürde vorgelegt der Philosophischen Fakultät II der Universität Zürich von THOMAS GEISSMANN von Hägglingen Begutachtet von den Herren Prof. Dr. R.D. Martin Dr. D.J. Chivers Zürich 1993 Zentralstelle der Studentenschaft Suggested citation: Geissmann, T. (1993). Evolution of communication in gibbons (Hylobatidae). Ph.D. thesis, Anthropological Institute, Philosophical Faculty II, Zürich University, Switzerland. iii + 374 pp. (English text, German summary). Contents: 1. Introduction ................................................................................................1 1.1 Introduction to Gibbons.....................................................................1 1.2 Gibbon Ancestry...............................................................................2 1.3 Gibbon Systematics ..........................................................................4 1.4 Adopting a Systematic Framework....................................................7 1.5 Aims of the Present Study...............................................................10 2. Material and Methods...............................................................................14 2.1 General Methods.............................................................................14 2.2 Vocal Communication.....................................................................15 2.3 Olfactory Communication................................................................21 2.4 Visual Communication....................................................................32 2.5 Phylogenetic Evaluation ...................................................................33 3. Vocal Communication...............................................................................35 3.1 Introduction.....................................................................................35 3.2 Pure Species Vocalizations..............................................................43 3.3 Hybrid Vocalisations.......................................................................53 4. Olfactory Communication.........................................................................82 4.1 Introduction.....................................................................................82 4.2 Macroscopic Study .........................................................................97 4.3 Microscopic Study........................................................................118 4.4 Chemical Analysis.........................................................................124 5. Visual Communication............................................................................139 5.1 Description of Visual Characteristics ............................................139 5.2 Circumfacial Markings in Siamangs .............................................144 5.3 Body Weight.................................................................................155 6. Phylogenetic Evaluation..........................................................................162 6.1 Description of the Data Matrix......................................................162 6.2 Analysis of the Complete Data Matrix ..........................................162 6.3 Analysis of Subsets of the Data Matrix.........................................169 7. Discussion..............................................................................................174 7.1 Vocal Communication...................................................................174 7.2. Olfactory Communication..............................................................203 7.3 Visual Communication..................................................................215 7.4 Phylogenetic Evaluation .................................................................229 ii Evolution of Communication in Gibbons 8a. Summary ................................................................................................234 8b. Zusammenfassung..................................................................................240 9. References ..............................................................................................247 10. Appendices .............................................................................................278 Appendix 10.1: Tape-Recorded Songs of Hybrid Gibbons....................279 Appendix 10.2: Vocal Characteristics of Gibbons ..................................283 Appendix 10.3: Study Animals for Olfactory Communication ...............286 Appendix 10.4: Skin Secretions..............................................................302 Appendix 10.5: Olfactory Characteristics of Gibbons ............................307 Appendix 10.6: Visual Characteristics of Gibbons .................................308 Appendix 10.7: Key to Abbreviations for Museum Collections..............311 Appendix 10.8: Key to Abbreviations for Collectors ..............................312 Appendix 10.9: Individual Data on Body Weights .................................313 Appendix 10.10: Gazetteer......................................................................350 Appendix 10.11: "Non-communicatory" Characteristics of Gibbons .....365 Appendix 10.12: Data Matrix for Phylogenetic Evaluation.....................368 11. Acknowledgements.................................................................................371 12. Curriculum Vitae.....................................................................................374 "Whether the species maintain their individuality through geographical segregation, or whether, if they were to meet and mix, sexual and social instincts would still maintain the present arrangement of species, are matters upon which no information has as yet been given. But the fact that certain of these species (H. lar, H. pileatus, and H. hoolock), if not all, have voices which can be distinguished, tends to show there is a physiological differentiation, and the colour markings are very constant." (Keith, 1896) "Um zu wissen, ob ein Gebiet von dieser oder jener Art bewohnt sei, ist es übrigens nicht immer nötig, ans Land zu gehen; man kann zuverlässig feststellen, welche Art hier vorkommt. Die Stimme der Hylebatiden ist nämlich sehr laut und bei den einzelnen Arten sehr verschieden." (Volz, 1904) 1. Introduction 1 1. Introduction 1.1 Introduction to Gibbons The gibbons, or lesser apes (Hylobates spp.), are distributed throughout the tropical rain forests of Southeast Asia (Chivers, 1977; Groves, 1972; Marshall & Sugardjito, 1986). They are unusual among primates in several respects which can be summarised under three key complexes: locomotion, social structure, and communication. Gibbons are strictly arboreal and mainly frugivorous (Chivers, 1984a; Leighton, 1987). Their arm-swinging form of locomotion (brachiation), unique suspensory behaviour and habitual erect posture represent extreme specialisations which evolved in connection with the animals' substrate and diet (Chivers, 1984b). Gibbons live in monogamous, territorial family groups (Brockelman & Srikosamatara, 1984; Chivers, 1984b; Leighton, 1987). In the wild, single offspring are born at intervals of approximately 3 years. Offspring remain with their parental family group until attaining sexual maturity at about 8 years of age, at which time they usually leave the group in order to find a mate and a territory. All species of gibbons are known to produce elaborate, species-specific and sex-specific patterns of vocalisation often referred to as "songs" (Haimoff, 1984a; Marshall & Marshall, 1976, 1978). Songs are loud and complex and are mainly uttered at specifically established times of day. In most species, mated pairs may characteristically combine their songs in a relatively rigid pattern to produce coordinated duet songs. Several functions have been attributed to gibbon songs, most of which emphasise a role in territorial advertisement, mate attraction and maintenance of pair and family bonds (Haimoff, 1984a; Leighton, 1987). 2 Evolution of Communication in Gibbons 1.2 Gibbon Ancestry Various fossil primates have at some time or other been proposed as possible ancestors of gibbons, including genera from the Oligocene such as Propliopithecus (= Aeolopithecus) and from the Miocene such as Crouzelia, Dendropithecus, Dionysopithecus, Laccopithecus, Limnopithecus, Micropithecus, Pliopithecus (see e.g. Barry et al., 1986; Fleagle, 1984; 1988). Most of them are probably too primitive to be gibbon ancestors and probably precede the radiation of living hominoids; in others, the critical cranial and postcranial material is not available (Fleagle, 1984; 1988). In many cases, phyletic relationship with hylobatids has been assumed on the basis of dentition (5-cusped, ape-like molars) and small body size. A major problem in tracing gibbon ancestry is that modern gibbons are defined as a clade mainly by derived postcranial features related to brachiation (Andrews & Groves, 1976), whereas, so far as known, none of the previous candidates for hylobatid ancestors seems to exhibit such features (Barry et al., 1986; Fleagle, 1984). On the other hand, gibbon