Abstract # 137:

Scheduled for Saturday, June 21, 2008 10:30 AM-10:40 AM: Session 15 (Meeting Room 2DEF) Oral Presentation

The importance of shape in primate sexual swellings: evidence from wild chacma baboons (Tsaobis Leopard Park, Namibia) and free-ranging mandrills (CIRMF, Gabon)

E. Huchard1,2, J. Benavides1, J. M. Setchell3, M. J. Charpentier4, L. A. Knapp5, G. Cowlishaw2 and M. Raymond1
1University Montpellier II, France, CNRS UMR 5554, Montpellier, France, 2Institute of Zoology, London, 3Evolutionary Anthropology Research Group, Durham University, UK, 4Department of Biology, Duke University, USA, 5Department of Biological Anthropology, University of Cambridge, UK
     The sexual swellings exhibited by female primates around ovulation are highly variable in size, shape and colour, but most studies have focused on their size. This study investigates the functional significance of sexual swelling shape. Using a morphometric method, we derived quantitative estimates of the two-dimensional shape of sexual swellings in two primate populations: 14 wild chacma baboons (Papio ursinus) from Namibia and 18 semi free-ranging mandrills (Mandrillus sphinx) from Gabon. Using linear mixed models (LMMs), we found that the two species exhibited different swelling shapes [F(1,31)=62.5, p<0.001], and that swelling shape is an enduring characteristic of individual females across oestrous cycles [baboons: c2(1)=308.5, p<0.001, mandrills: c2(1)=12.4, p<0.001]. Using 80 human judges, we confirmed that individual shape differences were visually detectable within both species [Binomial Sign Test, a=0.05; p<0.001 for both species]. Finally, an analysis (using LMMs) of the effect of female age, rank, and troop on swelling shape revealed an influence of the signaller’s age [baboons: F(1,10)=14.6, p<0.01, mandrills: F(1,18)=10.5, p=0.01]. In both species, the width of the basal apex of the swelling, relative to its top, is narrow in youth and becomes broader with age. Female age influences fertility in many primates and tightly reflects the parity in these mandrills. Our findings therefore suggest that primate swelling shape conveys information about species and individual identity, but also the signaller’s age, thus potentially fertility and/or past reproductive performance.