In dolphins, popular boys have more babies

New research from scientists at the University of Zurich looked at the social lives of male dolphins living in Shark Bay, Western Australia. Analyzing 30 years of behavioral observations of 85 male dolphins as well as paternity tests for over 400 dolphins, they made some interesting discoveries. 

“Understanding determinants of differential reproductive success is at the core of evolutionary biology because of its connection to fitness. Early work has linked variation in reproductive success to differences in age, rank, or size, as well as habitat characteristics. More recently, studies in group-living taxa have revealed that social relationships also have measurable effects on fitness,” wrote the study authors. “The influence of social bonds on fitness is particularly interesting in males who compete over reproductive opportunities.

It turns out that male dolphins form strong social bonds among themselves, creating stable alliances. These alliances work together to compete with each other for access to females and defending each other.   

“This kind of male cooperation for the purpose of reproduction is highly unusual in the animal kingdom. It’s only been observed in a much less complex form in some other primates,” said Livia Gerber, a former PhD student at the Department of Anthropology of the University of Zurich. 

Interestingly, how popular an individual male dolphin is impacts the size and strength of his alliance. The size and strength of the alliance in turn affects how successful a male dolphin may be at stealing females away from other alliances and mating. 

“Our study is the first to show that social bonds among male dolphins positively impact their reproductive success and are, therefore, directly linked to fitness,” said senior author Michael Krützen. “This had previously only been observed in male chimpanzees and some other primates. Our study expands upon previous findings on land mammals and provides compelling evidence that such highly complex, multi-level social systems also developed independently in the ocean.”

Social interaction among males and some other animals is incredibly common and important, sometimes even for survival. This research shows that it is important for reproduction as well, having important implications for evolution. It may be even that this sort of reproductive success could drive the evolution of social bonds in general. Future research could shed more light on this idea in dolphins as well as other animals.   

The study is published in the journal Current Biology.

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By Zach Fitzner, Earth.com Staff Writer