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Female dolphins that "hang-out" with other mums are themselves more successful as mothers according to an international team of behavioural scientists.

The authors of the report, published today in the journal Proceedings of the National Academy of Sciences, studied how inherited genetic characteristics and social factors influenced the reproductive success of a group of bottlenose dolphins in Shark Bay, Western Australia.

Dr Celine Frere led the research at the University of New South Wales, in Sydney, and she says that good genes are only part of the picture; and that an individual's social network has a strong influence on reproduction.

The team used calving success, where the offspring survive infancy (past three years of age), as their gauge.

"We found that genetic effects only account for 16% of variation in calving success amongst the female dolphins, whereas social factors are a much stronger determining factor - they are almost three times as important as having good genes," says Frere.

Dolphin mums tend to spend about half of their time alone with their calves and although they also spend time with family, their preferred 'mothers' group' associates are typically unrelated.

These dynamic interactions have meant that, until now, it has not been possible to evaluate the individual contribution of genetic and environmental factors, one of which is social bonding. Frere says that the mathematical methods to do so have only been developed in the last few years.

In this study, the researchers analysed twenty-five years of observational data from 52 female dolphins which detailed the number of offspring and whom they associated with.

This information was combined with DNA results to establish how closely related the dolphins in the group were.
Friends over family

Frere explains that while having successfully reproducing female family members, such as sisters and aunts, boosts a female's calving success, having unrelated successful associates is more important.

Notably, the researchers were also able to demonstrate that a female dolphin with good genes and strong social bonds with other mums is likely to have higher calving success.

"Although we can't put a numerical value on this, we can say that these dolphins are likely to be much more successful," says Frere.

"We aren't sure why these females come together, it may be for combined protection of the offspring from male harassment or predation, or there may be other social benefits," she says.

Dr Rochelle Constantine of the School of Biological Sciences at the University of Auckland, New Zealand says the study is exciting and unique.

"Bottlenose dolphins can live for around forty to fifty years and you need a study of this length to obtain meaningful data. Its impact cannot be under-estimated", she says.

Constantine explains that this research is invaluable when considering the use of specific marine areas for activities such as tourism and fishing.

"For long-lived animals like bottlenose dolphins, who have a large home-range and complex social structure, we can't now assume that if displaced they'll readjust because, along with environmental factors, their success relates to that of their associates," she says.

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