Female chimps keep the bullies at bay

Mar 07, 2007

Female chimpanzees may have found a fool-proof way to ensure they mate with only the highest ranking males, namely those with important social and physical characteristics that their offspring may inherit, according to a new study by Akiko Matsumoto-Oda from the Department of Welfare and Culture at Okinawa University in Japan.

Female chimpanzees do not synchronize their reproductive activities which reduces the opportunities for less-desirable males to coerce them into mating. The findings have just been published online in Springer's journal Behavioral Ecology and Sociobiology.

Most studies of primates to date have suggested that females synchronize their reproductive activities. However, it has been very difficult to demonstrate this analytically. Matsumoto-Oda and colleagues have developed a new index – the estrus synchrony index - to analyze whether female chimpanzees, in the Mahale Mountains National Park in Tanzania, synchronize the fertile period of their reproductive cycles.

The authors identified estrus in females by the size of their anogenital swellings, which is related to increased levels of follicular estrogen. The period of maximal swelling was regarded as the 'estrous period' because almost all copulations were observed in this phase. In the analysis of the data covering nine years of observations, the authors looked at whether or not females displayed a significant tendency to synchronize their estrous cycles.

Commenting on these findings, the authors suggest that "avoiding synchronizing estrous cycles may be a female strategy to reduce male sexual coercion."

Indeed, male chimpanzees use coercive tactics such as physical aggression against females, forced copulation, harassment and intimidation to increase their reproductive success. The opportunity for males to coerce females is reduced when females avoid synchronizing their estrous cycles, because with fewer females in estrous at the same time, mating competition between males intensifies. As a result, there is an increased probability that high-ranking males, with desirable social and physical attributes, will mate with the fertile females. These sought-after characteristics could be inherited by their offspring.

Source: Springer

Explore further: How researchers are speeding up seed production for new wheat

add to favorites email to friend print save as pdf

Related Stories

Biologists link sexual selection and placenta formation

Jul 09, 2014

Sexual selection refers to species' selection for traits that are attractive to the opposite sex. This special type of natural selection enhances opportunities to mate, the tail of male peacocks being an ...

Transgender algae reveal evolutionary origin of sexes

Jul 08, 2014

Throughout evolution, living things have repeatedly developed physically distinct sexes, but how does this actually happen? A discovery in the multicellular green alga, Volvox carteri, has revealed the genetic ...

Flower's bellows organ blasts pollen at bird pollinators

Jul 03, 2014

A small tree or shrub found in mountainous Central and South American rainforests has a most unusual relationship with the birds that pollinate its flowers, according to a study reported in the journal Current Bi ...

Light pollution alters reproduction cycle in lemurs

Jul 02, 2014

Besides obscuring the stars, light pollution can also disrupt the reproduction of light-sensitive animals. French scientists have shown that light pollution can override the natural reproductive cycle of ...

Recommended for you

User comments : 0