Chimpanzee female: mating call as a competitive strategy

Aid from male partners against competing females

Chimpanzee females avoid competition for partners © Cristina Gomes / MPI for Evolutionary Anthropology
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Chimpanzee females emit loud calls during mating. However, these are not intended to incite the competition of males with each other, as previously believed. Instead, the females use the calls strategically to claim their protection and support from the potential male partner - against competing females.

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When chimpanzees copulate with each other, the females repeatedly emit so-called copulative calls. Previously, the researchers had assumed that these calls are directed to the males signals to increase the competition between them. Because unlike Homo sapiens such Schäferstündchen remain undisturbed - in fact, the sexual act is often interrupted by other males. These then also try to copulate with the female in order to send their sperm into the race in this way.

After the common theoism of the "sperm competition" in the end it is simply about who bears witness to the most surviving progeny. The copulation calls of the female thus have only the goal to win the strongest partner, who testifies the best possible offspring, for themselves.

No connection to fertility

But this theory does not explain the behavior of free-living chimpanzees, which the psychologists Simon Townsend and Klaus Zuberbühler and the biologist Tobias Deschner of the Max Planck Institute for Evolutionary Anthropology have now observed in their study in the Budongo Forest (Uganda). The researchers found that females produced copulation calls more frequently when high-ranking males were within earshot. However, they concealed their sexual activities when other females of higher rank were nearby. display

In addition, hormone studies showed that the recall activity did not correlate with the fertility status of the female. "By means of progesterone levels in urine, we can precisely determine the time of ovulation, ie ovulation, " explains Tobias Deschner. "However, the behavior of the chimpanzee females, especially the frequency with which they made their copulative calls, remained unchanged during this period. So they did not indicate by their behavior that they were receptive. "

Hard competition among females

The researchers therefore believe that chimpanzee females use their copulation calls in a very tactical manner to limit the risks of competing with other females and to ensure the protection of their potential male partners. The competition between females is very pronounced in free-living chimpanzees. In the Budongo Forest in Uganda, the aggression between the animals is so strong that researchers even observed infantile infestation by other females.

"Copulation calls may be a strategy adopted by chimpanzee females to alert high-ranking males to receptivity, confusion over paternity, and in this way support socially important individuals secure, "says Simon Townsend.

(MPG, 19.06.2008 - NPO)