Estrus asynchrony in chimps

Just want to quickly point out some interesting reading that popped up in this month’s issue of Behavioral Ecology and Sociobiology (and in a LiveScience post). Estrus cycle asynchrony in wild female chimpanzees, Pan troglodytes schweinfurthii. The authors (Matsumoto-Oda, et al.) highlight the prevalence of the synchronized cycle mating strategy (among primates and other animals) before examining their current research statistic: the Estrus Synchrony Index (ESI), which focuses on maximal swelling and periovulatory periods.

ESI = var (Fm/Fc)/[mean(Fm/Fc){1 – mean(Fm/Fc)}]

Fm = the number of females in maximal swelling
Fc = the number of cycling females

In short, the group of chimpanzees studied exhibited asynchronous estrus cycles.

While some animals synchronize reproductive cycles to benefit from typical things like the wet season (abundance of food), safety in numbers, alloparenting, etc., chimps are cycling at different times to potentially benefit from a reduction in female-female mate competition and a reduction in male sexual coercion.

“Synchrony avoidance may therefore represent a tactic that permits a female to exercise limited choice for high-ranking males, rather than mating the first male that encounters and coerces her.”

It’s an interesting and seemingly appropriate find given the social structure of chimpanzee groups. I wonder what else there is to it… is there any rhyme or reason amongst the asynchrony? Are dominant females cycling so that they give birth when environmental conditions are at their best?

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