Monday, November 21, 2011
In a study of wild primates, reported this week in the Proceedings of the National Academy of Sciences, University of Wisconsin-Madison anthropologist Karen B. Strier and her colleagues, including University of Texas at Austin associate professor of anthropology Anthony Di Fiore, describe patterns of paternity in a monkey society where equality and tolerance rule and where sexually mature males, still living at home, seem to get helpful access to mates by the mere presence of their mothers and other maternal kin.
The new study, which combines Strier’s long-term behavioral studies of wild muriquis with new genetic assays obtained from their scat, is important because relatively little is know about patterns of male reproductive success in wild primates, much less ones with the muriqui’s unique egalitarian social system.
“The idea of looking at genetic paternity in the muriquis grew out of conversations I had with my Brazilian colleagues more than a decade ago, but it wasn’t until we teamed up with [Di Fiore] that the study could be realized,” Strier says.Di Fiore’s expertise combines the noninvasive analyses of genetic paternity in wild primates with an interest in behavioral ecology and evolution-a combination that proved to be a perfect fit for new analyses on long-term behavioral questions about these unique primates. Recent improvements in techniques for extracting DNA from scat, as well as the identification of variable genetic markers useful for genotyping animals and for population-level analyses finally made it possible for a study like this to be done, Di Fiore says.
“We believe this is the first piece of research to look at the distribution of paternities across males in any primate species where male social relationships are egalitarian,” Di Fiore notes, meaning that researchers cannot detect any sort of dominance hierarchy or dominance relationships among the males.
The northern muriqui is a large, long-lived, socially complex and critically endangered New World primate. There are at most 1,000 animals left in patches of the Brazilian Atlantic Forest, the only place the species is found.
“The kind of society that northern muriquis live in is very rare among primates. Lots of different males mate with females, and our results show that the number of kids that a male sires isn’t age or dominance related, as is true for many other primates such as baboons or chimpanzees,” Di Fiore says. “That’s a very unique situation.”
But the study’s big surprise was evidence that could extend the ‘grandmother hypothesis,’ the notion that human females evolved to live well past their reproductive years because of the advantages that post-menopausal women might confer on their offspring’s own reproduction, to other long-lived primates.
“The new data show who’s pulling the strings in muriqui society,” Strier says. “It’s the mothers.”
Genetic data from 67 monkeys – infants, mothers and possible sires – were analyzed, and the genetic results validate previous behavioral observations, and provide a new window into muriqui society.
“It would be really interesting now to look at paternity in other muriqui populations and in other species where mothers and sons stay together for life, to see if there are similar maternal effects,” Strier says.
Intriguingly, no infants were the result of mating between males and a close maternal relative. “The finding that no inbreeding is occurring is important,” Strier says. “Mating may be less random than we think because of the influence of mothers and other maternal kin. There must be some mechanism of recognition or avoidance.”
This is an important discovery that may also help with muriqui conservation, says Strier, given that the 300 or so muriquis in her study population are found in a protected reserve, where they are isolated from other muriquis and, potentially, at risk from inbreeding depression. The data suggest that this muriqui population, despite its isolation, may be large enough for its members to avoid close inbreeding, at least over the short term, as conservationists work to preserve and expand habitats for other existing groups.