Why do capuchin monkeys urine wash? An experimental test of the sexual communication hypothesis using fMRI
Article first published online: 15 FEB 2011
© 2011 Wiley-Liss, Inc.
American Journal of Primatology
Special Issue: Special Section on Understanding Emotions in Primates: In Honor of Darwin's 200th Birthday
Volume 73, Issue 6, pages 578–584, June 2011
How to Cite
Phillips, K. A., Buzzell, C. A., Holder, N. and Sherwood, C. C. (2011), Why do capuchin monkeys urine wash? An experimental test of the sexual communication hypothesis using fMRI. Am. J. Primatol., 73: 578–584. doi: 10.1002/ajp.20931
- Issue published online: 20 APR 2011
- Article first published online: 15 FEB 2011
- Manuscript Accepted: 25 DEC 2010
- Manuscript Revised: 22 DEC 2010
- Manuscript Received: 8 SEP 2010
- urine washing;
- olfactory communication;
Urine washing (UW) consists of depositing urine on the hands and vigorously rubbing the body. As urine contains chemical and pheromonal cues, UW may convey socially relevant information. Although ritualized UW is observed in many New World primates, including capuchin monkeys, the functional significance of UW remains unclear. In this experiment, we investigated the social signaling hypothesis of UW. Specifically, we hypothesized that UW by males conveys socially relevant signals that females can detect. We used functional magnetic resonance imaging (fMRI) to test whether adult female capuchins show differential brain activation in response to adult male and juvenile male capuchin urine. We expected to see changes in activation of structures involved in olfactory processing, including the piriform cortex, medial preoptic and anterior hypothesis, orbitofrontal cortex, hippocampus, and cerebellum. Data were acquired from four adult female capuchin monkeys. Presentations of odor stimuli (obtained from unfamiliar males) were made during fMRI acquisition using a standard ON-OFF design. All fMRI data were spatially normalized to a template and analyzed using the FMRI Expert Analysis Tool Version 5.98, part of the FMRIB's Software Library (www.fmrib.ox.ac.uk/fsl). Whole brain analyses revealed significant activations in the inferior temporal cortex, parahippocampal gyrus, precuneus, hippocampus, pulvinar, and cerebellum when females were presented with the adult male urine. Notably, significantly greater signal activation was observed in several regions associated with olfactory processing, when subjects were presented with adult male urine as compared with urine from juvenile males. Our results indicate that UW serves a social communicative function in capuchins, providing support for the sexual signaling hypothesis. Am. J. Primatol. 73:578-584, 2011. © 2011 Wiley-Liss, Inc.