Aggressive, Competing Males May Stress Out Female Chimps

It turns out that male chimps vying for a female's affection may just be hurting themselves. Scientists have found that the aggressive tactics of male chimps might just lower a female's chances of conceiving.

Female chimps have an extremely slow reproductive cycle. In fact, they only give birth every five to seven years. When they're ready to reproduce, they display large swellings of their genitals and often do so for several months before conceiving. During this time, male chimps can often compete fiercely for the attention of the female. While mating with many males can ensure that their young are not killed by jealous males, the harassment and jealous guarding by males can also influence the ability of females to feed.

Intrigued by this, the scientists spent more than 11 years observing the daily interactions and diets of 50 members of the Kanyawara community of East African chimps. They collected urine samples from 25 females, either by capturing falling urine from a plastic bag or by pipetting urine from plants. They then gauged the levels of C-peptide and estrogen and progesterone in the urine.

What did they find? It turns out that the more males gathered around a female during a given month, the lower her C-peptide levels. In contrast, the number of females she associated with had no effect. Declining C-peptide levels mean that the female is spending more energy than she consumes, which can result in weight loss.

"This has significant downstream effects on females' reproductive functioning and fertility rates, and demonstrates that the reproductive tactics of male chimps could put a damper on the ability of the female members of their species to conceive," said Emery Thompson, one of the researchers, in a news release.

The findings reveal how too many males may just influence the reproductive capabilities of females. This could have implications for breeding programs for chimps.

The findings are published in the journal Behavioral Ecology and Sociobiology.