Size of Sexual Swellings Reflects Ovarian Function in Chimpanzees (Pan troglodytes)

While many theories exist on the evolution of the sexual swelling signal in female primates, the significance of the very large and variable swellings found in some catarrhine primates is still debated. As suggested by Pagel [(1994) Anim Behav 47:1333-1341], these exaggerated and costly signals have...

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Bibliographic Details
Published in:Behavioral ecology and sociobiology 2003-09, Vol.54 (4), p.340-351
Main Authors: Emery, Melissa A., Whitten, Patricia L.
Format: Article
Language:English
Subjects:
Animal reproduction
Anthropology
Baboons
Behavioral biology
Chimpanzees
Estrogens
Evolutionary biology
Female animals
Females
Male animals
Mating behavior
Ovulation
Primates
Reproductive cycle
Reproductive system
Steroids
Swelling
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Summary:While many theories exist on the evolution of the sexual swelling signal in female primates, the significance of the very large and variable swellings found in some catarrhine primates is still debated. As suggested by Pagel [(1994) Anim Behav 47:1333-1341], these exaggerated and costly signals have the potential to provide information about differential female reproductive quality to males. While Domb [(2000) Department of Anthropology, Harvard University, Cambridge] and Domb and Pagel [(2001) Nature 410:204-206] propose that swellings serve to reliably indicate between-female fitness differences, we hypothesize that they may indicate current reproductive cycle quality, within or between females. This study examines the between-cycle relationship between ovarian function, gauged via fecal steroid analysis, and absolute size of sexual swellings, yielded through photogrammetric methods. Fourteen cycles from eight captive, group-living chimpanzees (Pan troglodytes) exhibited considerable variability both in ovarian steroid levels and maximum sexual swelling size. Nearly all measures of a female's maximal swelling in a cycle correlated with early follicular and early luteal estradiol averages and the duration of luteal progesterone elevation. Swelling area was also correlated with late follicular estradiol. Given past evidence that such measures of ovarian function predict conceptive success, these data strongly suggest that swellings could convey information to competing males about the fecundability of a potential mate.
ISSN:0340-5443
1432-0762
DOI:10.1007/s00265-003-0648-6