Imagine that by smelling someone, you could understand their genetic diversity, immune system health and potential as a mate.
A recent Duke study in the lab of Christine Drea, Earl D. McLean professor in evolutionary anthropology, examined this very phenomenon in ring-tailed lemurs. The experiment, which started in 2008, looked at the chemical composition of ring-tail lemur stink-gland secretions to examine whether specific genetic markers corresponded to the mating preference of lemurs.
“Ring-tail lemurs are this really fascinating primate species,” said Kathleen Grogan, a former Ph.D. candidate at Duke and lead author on the paper. “We think of primates as visually oriented, and it turns out that primates actually use their sense of smell a lot more than we think they do.”
During a short breeding season, female ring-tailed lemurs who are ready to reproduce use their strong sense of smell to determine which male will produce the best offspring.
“It’s quite funny to see ring-tailed lemurs,” said Sally Bornbusch, a graduate student in the Drea Lab, of the comical mating ritual used by male ring-tail lemurs during the breeding season. “In particular, males will scent mark their own tail. So, they’ll bring their tail up, rub their wrists on their tail and then bring it over their head and wave it at a female. It’s called stink fighting.”
Although this process of “stink fighting” has been previously observed both in the territorial disputes and mating behavior of lemurs, the question of what the lemurs smell and why they prefer one scent to another stood unanswered. Put simply, is lemur love nose-blind?
“We know that the scent mark of a ring-tail lemur differs if you’re a male or a female,” Grogan said. “It differs if you’re a juvenile or an adult, if you’re in breeding condition or if it’s the breeding season.”
She explained that prior to her years at Duke, researchers discovered that genetic diversity was correlated with variation in scent glands—that is, more diverse animals tend to have more complex scent glands.
This discovery then led Grogan and her team to look specifically at the major histocompatibility complex (MHC), a genetic marker considered one of the most important adaptive immune genes in primates.
Because this gene is so heavily connected to the immune health of a host, Grogan investigated whether genes that exist in the scent secretions of ring-tails inform a female lemur’s perception of male immune genetic diversity.
The answer was a resounding yes; the study not only found a correlation between immune fitness and the concentration of MHC in male gland secretions, but also that females tend to prefer males with more diverse MHC concentrations.
Although Grogan has hypothesized that females may use the MHC in their gland secretions to ward off or challenge a rival male, further research is needed to better understand how these hormones impact day-to-day interaction outside of the breeding season.
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This study has interesting implications for captive lemur breeding programs. Erin Ehmke, director of research at the Duke Lemur Center, explained the captive breeding process in their facility is a partially involuntary one. Since most lemur species are endangered, captive lemurs rarely, if ever, get to choose their own mate. Rather, they are usually paired based on lineage. However, understanding the genetic implications of MHC in lemur reproduction can make the mating process in captivity easier and more impactful.
This study has the potential to have wider implications. “All lemurs use smell to the extent that ring-tails do,” Ehmke stated. “Everything they do uses scent and scent glands.” Although ring-tail olfactory systems tend to be more complex than those of other lemur species, lemur behavior, even human behavior, can be linked to similar smell-based indicators.
Grogan hinted that the appreciation of MHC diversity may not be limited to lemurs.
“We think humans...can detect this MHC variation, and human females may prefer the scent of more MHC diverse guys,” Grogan said. “There are studies that show that Mandrills make mate choices based on MHC diversity, and there’s some work to show that Mouse Lemurs do so too.”
Correction: The study took place in Christine Drea's lab, not Dorothea. The Chronicle regrets the error.