Sources of variance in a female fertility signal: exaggerated estrous swellings in a natural population of baboons
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Signals of fertility in female animals are of increasing interest to evolutionary biologists, a development that coincides with increasing interest in male mate choice and the potential for female traits to evolve under sexual selection. We characterized variation in size of an exaggerated female fertility signal in baboons and investigated the sources of that variance. The number of sexual cycles that a female had experienced after her most recent pregnancy (“cycles since resumption”) was the strongest predictor of swelling size. Furthermore, the relationship between cycles since resumption and swelling size was most evident during rainy periods and was not evident during times of drought. Finally, we found significant differences in swelling size between individual females; these differences endured across cycles (i.e., were not explained by variation within individuals) and persisted in spite of ecological effects. This study is the first to provide conclusive evidence of significant variation in swelling size between female primates (controlling for cycles since resumption) and to demonstrate that ecological constraints influence variation in this signal of fertility.
KeywordsBaboon Estrous swelling Fertility
We thank the Office of the President of the Republic of Kenya, the Kenya Wildlife Service and its Amboseli staff and wardens, the Amboseli-Longido pastoralist communities, Ker & Downey Safaris, and Tortilis Camp in Amboseli for their cooperation and assistance in Kenya. This research could not have been conducted without assistance to CLF from L. Maryott and from the US Embassy in Nairobi during multiple critical times. We thank the Amboseli Baboon Research Project long-term senior field researchers (R.S. Mututua, S. Sayialel, and J.K. Warutere) and the research assistants (G.Y. Marinka, C.S. Mutenkere, and B.O. Oyath) for their invaluable assistance and insight. Many people have contributed to the long-term data collection and database maintenance; in particular we thank L. Maryott, T. Fenn, and N. Learn. We thank Jeff Jacobsen for early assistance with the Photoscale-2 method. We thank Mine Cetinkaya-Rundel and the Duke Statistical Consulting Center for help with our analyses. We thank Elise Huchard, James Higham, Dietmar Zinner, and one anonymous reviewer for constructive comments that improved an earlier version of this article. CLF was supported by Sigma Xi, Duke University Center for International Studies, Duke Biology, the Princeton Center for the Demography of Aging (P30AG024361), the Patricia William Mwangaza Foundation, the L.S.B. Leakey Foundation, an NSF Graduate Research Fellowship, and a Fulbright Fellowship. Support for the long-term research project was provided by the National Science Foundation (most recently IOS 1053461 and DEB 0919200) and the National Institute of Aging (R01AG034513 and P01 AG031719). Support data from this project are available in the Dryad database: doi: 10.5061/dryad.bb7c3.
This study complies with regulations for both the USA and Kenya regarding the ethical treatment of research studies.
Conflict of interest
The authors declare that they have no conflict of interest.
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