Fertile friendships between a male dolphin – wissenschaft.de

A friendly factor in reproductive success: In the case of dolphins, males who have many friends and are therefore particularly well integrated into the male alliance system produce the most offspring. This arises from paternity tests and data from long-term monitoring of animals in Australian Shark Bay. Scientists say this once again clarifies the complex meanings of the highly evolved social system of intelligent marine mammals.

Completely different and yet very similar to us: Dolphins’ bodies are adapted to life in the water, but their cognitive abilities and behavior show striking similarities with humans. In addition to their high level of intelligence, this also applies to their complex social behavior, which is characterized by “personal” bonds between animals: marine mammals form very stable and supportive alliances with each other. They communicate using a rich repertoire of sounds that are widespread in the underwater world. Studies show that dolphins use certain sound patterns as “names” to identify each other.

Collaboration for the winners

Many ideas about the habitat and behavior of dolphins come from the Australian Shark Bay. Scientists have been studying a group of Indo-Pacific dolphin (Tursiops aduncus) there for 30 years. Male animals were the focus of their current study. According to a report by the team led by Livia Gerber of the University of Zurich, long-term studies have already documented that male dolphins live in complex social groups where they develop cooperative friendships with other males. The system is characterized by larger alliances of up to 14 individuals that remain quite stable over long periods of time. Within these bands there are also smaller, less symmetrical groups of two or three males.

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Previous investigations have shown that groups and subgroups play a role in winning over mating partners: “male associations” work together to prey on females from other alliances or to fend off similar attempts by other groups. “This kind of male cooperation for reproductive purposes is very unusual in the animal kingdom. Otherwise, it is found only in great apes and here in a much simpler form,” says Livia Gerber. Together with her international colleagues, she has now investigated how the personal network of relationships in male dolphins affects their reproductive success. Biologists have evaluated the behavioral data of 85 males over the past 30 years. They then correlated these findings with the results of paternity tests in Shark Bay, based on the genetic features of more than 400 dolphins.

Many friends – many grandchildren

As they report, evaluations have shown that males who are particularly popular – and have extensive relationships with as many friends as possible – have the greatest reproductive success. In detail, it shows that the size of the circle of friends and the desire to socialize are more important. The researchers report that partner loyalty within smaller groups of two or three variables is not reflected in reproductive success. “We have now shown for the first time that strong friendships between male dolphins have a direct impact on their evolutionary fitness. Something similar was previously known only in male chimpanzees,” says senior author Michael Crutzen.

As the researchers explained, different aspects can contribute to the greater crossbreeding success of good networkers. Social bonds can extend life expectancy and also have a positive effect on health and thus contribute to the lifelong reproductive success of male dolphins. However, according to the researchers, the deciding factor is probably something else: “Well-integrated males are likely to benefit from the advantages of better cooperation, and thus have easier access to resources such as food or mating partners. In addition, they are more resistant to partner loss. Other species have fewer but closer partners,” says Gerber.

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As she and her colleagues emphasize, the results are an important contribution to the study of the behavior of highly evolved animals. Because the effect of cooperation between social partners on the number of offspring has not been investigated so far. “Our study extends previous knowledge of land-dwelling mammals and impressively shows that – apart from this evolution – social systems with very complex, multi-level interactions also emerged in the sea,” says Crutzen.

Source: University of Zurich, specialized article: Current Biology, doi: 10.1016/j.cub.2022.03.027

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