The more stable social contacts a male bottlenose dolphin maintained with fellows of the same sex, the more offspring he fathered. This was observed by a research group led by biologist Livia Gerber from the University of Zurich. The team published their results in the journal Current Biology. Marine mammals live in a complex social network. From a relatively stable, larger group of 4 to 14 animals (“second-order alliance”), smaller groups (“first-order alliance”) form again and again, which together search for fertile females. The behavioral researchers evaluated data from 30 years of ten second-order alliances, a total of 85 male dolphins. They determined the reproductive success using genetic paternity analyses.
Bottlenose dolphins that formed a particularly large number of constant relationships within the large group produced the most offspring. The dolphins with frequently changing friendships, on the other hand, had fewer children. “Our study was the first to show that friendships among male dolphins have a direct impact on their reproductive success and thus their evolutionary fitness,” says Gerber. “Up until now, this was only known from a few land-living mammals.” Well-integrated males could probably make better use of the advantages of cooperation and thus have better chances with female dolphins. They are also more resistant to partner losses. The anthropologist says: “So it’s not always the strongest and most dominant males that achieve the greatest reproductive success, but the most social animals.”