Washington, July 15 (ANI): Rice University biologist Amy Dunham has put forward a new theory for one of primatology’s long-standing mysteries-why are male and female lemurs the same size?

In most primate species, males have evolved to be much larger than females, but this has not been found to be true in case of lemurs.

Some theories have suggested that environment played a role or that lemur social development was altered due to the extinction of predatory birds.”Scientifically, this is quite a big question that researchers have debated for over 20 years. I actually started doing research on lemurs as an undergraduate, working in Ranomafana (National Park in Madgascar), and the question about size monomorphism has bugged me since then,” said Dunham.In the new study, Dunham has offered one of the first new theories on lemur monomorphism in more than a decade.After conducting an exhaustive review of the observational work done on lemurs, Dunham concluded that male lemurs do guard their mates, just like other primates.

But unlike gorillas and other primates that fight for mating rights with females, male lemurs have evolved to passively guard their mates.They do this by depositing a solid plug inside the female’s reproductive tract just as they finish mating. The plug is deposited as a liquid protein but quickly hardens and stays in place for a day or two.

Since many female lemurs are sexually responsive to males for only one day out of the entire year, the plug serves the purpose of preventing other males from mating with the female, while also freeing the male to mate with other females during the brief time they are available.”If the female has a short receptivity period, as most lemurs do, then we hypothesize that this is likely to be an advantageous strategy,” said Dunham.To test their hypothesis, the researchers examined 62 primate species and found that copulatory plugs were most likely to occur in species where female sexual receptivity was very brief and where males and females were the same size.

This was true both for lemur species and for a few other species, like South American squirrel monkeys.The study has been published in the Journal of Evolutionary Biology. (ANI)