Doctoral Dissertation Research: Socioendocrinology of Male Reproductive Strategies in the Siamang (Symphalangus Syndactylus)

Project Details


This research seeks to clarify the evolutionary forces shaping the behavioral and hormonal profiles of male primates. In particular, it will explore the correlations between male endocrinology and male-male competition, parental effort and female reproductive state, in the context of monogamous and polyandrous mating systems.

Data will come from behavioral observation and non-invasive hormonal sampling of four monogamous and three polyandrous groups of siamangs (Hylobatidae: Symphalangus syndactylus) in Sumatra (Indonesia). Non-biohazardous hormonal extracts will be stored in the field and analyzed in the U.S.

These data will shed light on the co-evolution of many striking and poorly understood aspects of primate, including human, social and reproductive biology, such as intra- and intersexual aggression, pair bonding and paternal care. The intellectual contributions of this work fall into four broad areas:

First, this study will provide the first hormonal data on a wild monogamous and polyandrous (nonhuman) hominoid. These mating systems are extremely rare among mammals (about 3%), thus, these data are essential for the improvement of current models of mammalian social evolution.

Second, this investigation evaluates the hormonal and behavioral responses of pair-bonded males to different reproductive challenges (sexual competitors within or outside the social group). These data will therefore test the hypothetically important role of mate guarding in human male competition, and will expand the breadth of theories so far tested only in humans, such as 'mate poaching'.

Third, paternal care is a conspicuous feature of human behavioral biology, but rather exceptional among primates. By providing data on an additional biparental ape, this study will allow us, for the first time, to assess the generality of these human patterns, and clarify the conditions and constraints associated with male parenting.

Finally, recent experimental data shows that human male behavior is affected by female reproductive state (through visual or olfactory cues). An evaluation of similar effects on siamangs will contribute to the understanding of the origin and function of signaling versus concealment of ovulation in human and non-human primates. It will also help determining the social and ecological conditions under which female reproductive status affect male social and reproductive behavior.

One broader impact of this research is its contribution to conservation efforts: the study will improve the understanding of siamang demography and population dynamics, and will provide an accurate assessment of the impact of habitat deterioration and fragmentation.

The project will employ and train at least five local field assistants. In addition, the fieldwork of two Masters students at the University of Indonesia will be supported and supervised. Plans are being discussed to establish a primatology field school at Way Canguk, to further local education/conservation efforts.

Results will be disseminated through peer-reviewed publications and participation in professional meetings. This will help to guide future studies of proximate mechanisms (e.g. focusing on other hormones), psychological correlates, dispersal patterns, and female reproductive strategies in this group of socially monogamous apes.

Finally, this project will provide the awardee's with extensive practice with field endocrinology and laboratory procedures, and it will broaden the range of subjects he can offer to teach, as well as the expertise that he will bring to future working places.

Effective start/end date8/1/077/31/08


  • National Science Foundation: $14,958.00


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