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Research: Social Bonds Help Dolphins Breed

Janet Mann Dolphins

A recent study co-authored by biology professor Janet Mann suggests the success of a female dolphin’s calving is better explained by her interaction with female associates than by genetics.

November 1, 2010 – Georgetown biology professor Janet Mann has co-authored the first study showing the interaction of social and genetic factors on reproduction in a wild animal population.

The study shows that the success of a female dolphin’s calving is better explained by her interaction with female associates than by genetics.


Mann and University of Queensland scientist Celine Frére wrote the study, which was accepted by the prestigious Proceedings of the National Academy of Sciences (PNAS). The article appears in the online PNAS Early Edition on Nov. 1.

Dolphin Documentation
 

“Social experience and genes interact in complex ways,” says Mann, who will appear in a documentary Nov. 3 on BBC2, “but the social effects are stronger.”
 

Frére and Mann used data from the Georgetown professor’s 25 years of dolphin reproductive and behavioral research at Shark Bay in Western Australia and more than a decade of genetic samples collected by researchers at the University of New South Wales.
 

The study offers insights into the value of adaptive social skills among mammals, explains Mann, also a professor in the psychology department.

It Takes a Village
 

“Dolphins have long-term bonds that last for decades,” Mann explains. “It is likely females and their calves learn from each other about where to hunt or avoid predators such as tiger sharks. Females may also protect each other and their calves from shark attack.
 

“Also, when successful females spend more time together, their calves enjoy the social benefits of having more playmates.”
 

When Frére proposed the study, Mann was surprised it hadn’t already been done.
 

“Celine combined the genetic relatedness data with our long-term records on female association and calving success,” she explains.

Family vs. Friends
 

After examining the life histories of 52 female bottlenose dolphins, the scientists found that the positive reproduction effects were more important among unrelated females than related females. In other words, “friends” have a bigger impact on female reproduction than relatives.
 

“What this means is that although female kin are important in the lives of dolphins, social bonds with non-relatives have a substantial impact on female reproduction,” Mann says.

Past Findings Mixed
 

Previous research into reproductive success in animal populations has had mixed findings, Mann notes.
 

“Some studies pointed to the benefits of inherited genetic characteristics, while others showed the benefits of social effects, such as having the assistance of relatives or others,” she says.
 

In another study, published earlier this year, the research team showed that younger females are susceptible to inbred matings, which reduces their reproductive output because such calves are slower to wean.
 

The BBC2 documentary “Dolphins of Shark Bay” will air Nov. 3 in the United Kingdom. The film will be shown at a later date in the United States.

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