For dolphin mothers, successful parenting is as much a matter of having good friends as it is good genes.
The findings underscore the importance of community to dolphin life, and perhaps to animals in general -- something that's intuitively appreciated, but hasn't been directly compared to genetic fitness in a wild mammal population.
Some studies, including research on captive chimpanzees, have linked heredity to the survival rates of young animals. Research on wild horses has connected offspring survival to maternal sociality. But researchers had not yet compared nature and nurture directly.
"In wild populations, genetic heritability and the social components of fitness have not yet been examined together," wrote researchers led by University of New South Wales biologists Celine Frère and William Sherwin in a paper published Nov. 1 in the Proceedings of the National Academies of Science.
For 25 years, the researchers have made detailed observations of bottlenose dolphins in the eastern gulf of Australia's Shark Bay. That one-of-a-kind dataset allowed them to chart the relatedness of dolphin moms and map their habits of social association, then correlate these patterns to how well their offspring survived childhood.
As would be expected, calves born to moms from reproductively successful families tended to do well. But for dolphin moms from less-fit families, that lack of a pedigree was offset if they tended to hang out with successful moms. The researchers' analysis suggested that keeping good company was just as important -- even, at times, more important -- than coming from good stock.
That society could have such importance isn't shocking: Dolphins are extremely intelligent, with complex communities and powers of communication that some researchers consider comparable to language. (It's also in Shark Bay that evidence of dolphin tool use was famously found.) Nevertheless, "we can only speculate" as to the details of how females help each other, wrote Sherwin in an e-mail.
Close friends might help protect female dolphins from unwanted male attention, reducing inbreeding and resulting health problems, wrote Sherwin. Defense could also be important, especially during birth and early nursing stages. "The dolphin population we studied is in Shark Bay," he wrote.
Image: Flickr, Steve Jurvetson.
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Citation: "Social and genetic interactions drive fitness variation in a free-living dolphin population." By Celine H. Frère, Michael Krützen, Janet Mann, Richard C. Connor, Lars Bejder, and William B. Sherwin. Proceedings of the National Academy of Sciences, Vol. 107 No. 44, November 1, 2010.
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