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Friendships seen as key to success for dolphin moms

Nov. 1, 2010
Courtesy of the Uni­vers­ity of New South Wales
and World Science staff

Fe­male dol­phins who have help from fe­male friends are far more suc­cess­ful than oth­er dol­phin moms at rais­ing surv­iv­ing off­spring, ac­cord­ing to a new stu­dy.

The find­ing was based on 25 years of sci­en­tists’ ob­serva­t­ions at Shark Bay, West­ern Aus­tral­ia, and on ge­net­ic sam­ples tak­en over more than a dec­ade.

“Sur­pris­ingly, the ge­net­ic and so­cial ef­fects on re­pro­duc­tion have nev­er been stud­ied to­geth­er in nat­u­ral popula­t­ions,” said Bill Sher­win of the Uni­vers­ity of New South Wales, Aus­tral­ia, one of the re­search­ers. “One of my doc­tor­al stu­dents, Ce­line Frere, who led the lat­est stu­dy, real­ised that we could do so by us­ing the long-term ob­serva­t­ions about which fe­males were as­so­ci­at­ing with each oth­er, and put­ting that to­geth­er with what we knew about their ge­net­ic rela­t­ion­ships.”

Pre­vi­ous re­search in­to re­pro­duc­tive suc­cess among wild an­i­mals has had mixed find­ings. Some stud­ies point to the ad­van­tages of in­her­it­ed ge­net­ic char­ac­ter­is­tics. Oth­ers show the ben­e­fits of so­cial ef­fects, such as hav­ing un­re­lat­ed helpers some­times de­scribed as “honorary” aunts and un­cles.

The new stu­dy, billed as the first to look at the ef­fects of these fac­tors to­geth­er in a wild an­i­mal popula­t­ion, found that so­cial and ge­net­ic ef­fects are both im­por­tant. The work is pub­lished in this week’s early on­line is­sue of the re­search jour­nal Pro­ceed­ings of the Na­tional Acad­e­my of Sci­ences.

A dolphin mother’s re­pro­duc­tive or calving suc­cess was defined as the fre­quency with which she was seen to have a calf sur­viv­ing to three years of age.

Frere found that a fe­male’s calv­ing suc­cess is boosted ei­ther by so­cial as­socia­t­ion with oth­er fe­males that had high calv­ing suc­cess, or by the fe­male hav­ing rel­a­tives who are good at calv­ing.

“Not only that, but the so­cial and ge­net­ic ef­fects in­ter­act in an in­tri­guing way,” said Sher­win. “Hav­ing suc­cess­ful sis­ters, aunts and moth­ers around cer­tainly boosts a fe­male’s calv­ing suc­cess. But the ben­e­fits of so­cial as­sociates were more im­por­tant for fe­male pairs who were less ge­net­ic­ally re­lat­ed.”

Frere, now at the Uni­vers­ity of Queens­land, Aus­tral­ia said it’s un­clear why fe­male dol­phins need such help to be more suc­cess­ful moth­ers. “Dol­phins in this popula­t­ion are at­tacked by sharks, so pro­tec­tion by oth­er fe­males may help re­pro­duc­tion,” she said. She added that fe­males, es­pe­cially young­er ones, “may need pro­tec­tion against their own spe­cies as well.”


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Female dolphins who have help from their female friends are far more successful as mothers than other moms, according to a new study. The finding was based on 25 years of scientists’ observations at Shark Bay, Western Australia, and genetic samples taken over more than a decade. “Surprisingly, the genetic and social effects on reproduction have never been studied together in natural populations,” said Bill Sherwin of the University of New South Wales, Australia, one of the researchers. “One of my doctoral students, Celine Frere, who led the latest study, realised that we could do so by using the long-term observations about which females were associating with each other, and putting that together with what we knew about their genetic relationships.” Previous research into reproductive success among wild animals has had mixed findings. Some studies point to the advantages of inherited genetic characteristics. Others show the benefits of social effects, such as having unrelated helpers sometimes described as “honorary” aunts and uncles. The new study, billed as the first to look at the effects of these factors together in a wild animal population, found that social and genetic effects are both important. The work is published in this week’s early online issue of the research journal Proceedings of the National Academy of Sciences. Frere found that a female’s calving success is boosted either by social association with other females that had high calving success, or by the female having relatives who are good at calving. “Not only that, but the social and genetic effects interact in an intriguing way,” said Sherwin. “Having successful sisters, aunts and mothers around certainly boosts a female’s calving success. But the benefits of social associates were more important for female pairs who were less genetically related.” Frere, now at the University of Queensland, Australia said it’s unclear why female dolphins need such help to be more successful mothers. “Dolphins in this population are attacked by sharks, so protection by other females may help reproduction,” she said. She added that females, especially younger ones, “may need protection against their own species as well.”