Friendly factor in reproductive success: In the case of dolphins, those males who have many friends and are therefore particularly well integrated into the male alliance system produce the most offspring. This emerges from paternity tests and long-term observation data of the animals in the Australian Shark Bay. The scientists say that this shows once again the complex meanings of the highly developed social system of intelligent marine mammals.
So different and yet so similar to us: the bodies of dolphins are adapted to life in water, but their cognitive abilities and behavior show amazing parallels to humans. In addition to their high level of intelligence, this also applies to their complex social behavior, which is characterized by “personal” connections between the animals: the marine mammals form very stable alliances with each other and support each other. They communicate using a rich repertoire of sounds that spread far and wide in the underwater world. Studies even suggest that dolphins use certain sound patterns as “names” to identify one another.
Cooperation for winning females
Many insights into the living environment and the behavior of the dolphins come from the Australian Shark Bay. Scientists have been studying a population of the Indo-Pacific bottlenose dolphin (Tursiops aduncus) there for 30 years. The male animals were the focus of their current study. As the team led by Livia Gerber from the University of Zurich reports, the long-term studies have already documented that male dolphins live in complex social groups in which they cultivate 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 gangs, however, there are also smaller, less consistent groups of two or three males each.
From previous investigations it has emerged that the groups and subgroups play a role in winning mating partners: the “male associations” work together to poach females from other alliances or to ward off corresponding attempts by other groups. “This type of male cooperation for reproductive purposes is extremely unusual in the animal kingdom. It is otherwise only found in great apes and here in a much simpler form,” says Livia Gerber. Together with her international colleagues, she has now investigated the extent to which the personal network of relationships in male dolphins affects their reproductive success. The biologists evaluated the behavioral data of 85 males over the last 30 years. They then linked these results to results from paternity tests at Shark Bay, based on the genetic profiles of more than 400 dolphins.
Many friends – many descendants
As they report, the evaluations showed that the males who are apparently particularly popular – with intensive 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. Because the partner loyalty within the smaller, variably composed groups of two or three is not reflected in the reproductive success, the researchers report. “We have now shown for the first time that strong friendships among male dolphins have a direct impact on their evolutionary fitness. Something similar was previously only known in male chimpanzees,” says senior author Michael Krützen.
As the researchers explain, various aspects could contribute to the greater mating success of the good networkers. The social connections could lead to a longer life expectancy and also have a positive effect on health and thus contribute to the lifelong reproductive success of male dolphins. According to the researchers, however, the decisive factor is probably something else: “Well integrated males can probably make better use of the advantages of cooperation and thus have easier access to resources such as food or mating partners. In addition, they are more resistant to mate loss than conspecifics with fewer but closer partners,” says Gerber.
As she and her colleagues emphasize, the results are an important contribution to the study of the behavior of highly developed animals. Because the influence of cooperation among social partners on the number of offspring has hardly been investigated so far. “Our study expands the previous knowledge on land-living mammals and shows impressively that – independent of this development – social systems with extremely complex, multi-level interactions have also emerged in the sea,” says Krützen.
Source: University of Zurich, specialist article: Current Biology, doi: 10.1016/j.cub.2022.03.027