We’re at the Duke Lemur Center, and we have lengths of dowel, duct tape, grape jelly and two bags of craisins. Guess what’s going to happen next? Some construction? A fat-free picnic? A food fight? Well, no … actually we are with Katie Grogan, a Duke graduate student, who is going to use this equipment (and more, stay tuned!) to investigate the relationship between genetic fitness and mate choice in ring-tailed lemurs (Lemur catta).
It’s clear that Katie is passionate about lemurs. Bubbling with enthusiasm, she explains the twofold benefits of her research. Firstly, she hopes to answer the question, ‘Is there one best mate for everyone in the population, or is there one mate specific to each individual?’ Put in human terms, would Brad Pitt be the best mate for any human female, or should we all be searching for our individual ‘soul mate’? This is the first experimental test of mate preference in primates, and the results may be applicable to humans.
Secondly, and most importantly, are the benefits to lemur conservation. All lemurs are endangered. Currently, breeding decisions for captive animals are made by the American Association of Zoos and Aquariums, based on maintaining genetic diversity, but if this study shows that lemurs produce better offspring if they choose their own mates, it could change the way these decisions are made, to build up numbers and fitness of lemur species.
Using a molecule that controls the immune system in vertebrates, the MHC, Katie aims to find out whether the lemurs can distinguish between individuals with different genotypes, and if so, whether they prefer individuals with complementary genotypes to their own, or whether they are attracted to mates with the maximum heterozygosity, or genetic variation, regardless of their own genotype.
Lemurs do use odor to tell the difference between individuals, and this experiment is a choice test, giving male lemurs the choice of two female odors and noting their reactions to each. Today, however, is a habituation day, getting the lemurs used to coming down to check out the sticks – which is where the grape jelly comes in.
Our study participants, four male lemurs named Chandler, Limerick, Herodotus and Cebes, start bouncing around their enclosure when they see us coming. Actually, Katie reckons it’s the craisins that are causing all the excitement, and she could be right, as it is easy to separate the lemurs from one another using the craisins as a lure. Next, two wooden dowels are inserted into each enclosure and securely duct-taped in place. Each stick is spread with a smear of grape jelly, and we wait. Not for long, the lemurs have done this before, and soon they are licking, chewing, scent-marking and trying really hard to pull the sticks into the enclosure!
After a couple of days of the grape jelly treatment, the real experiment begins. The procedure is the same with the sticks and duct tape, but this time the lemurs are videotaped, and three sticks are presented to each lemur, two with different female odors and one control. The odors have been collected during regular vet examinations of the lemurs, using tiny sterilized cotton swabs, and stored in vials. The odors have to be from lemurs previously unknown to the study participants, and Katie has spent time at other facilities around the country collecting samples.
Herodotus is the first to be tested. He watches the setting up, then climbs quickly down to check out the sticks. He is very interested in the odors, sniffing, and scent-marking enthusiastically with his wrist and shoulder glands. After a couple of minutes of intense interest, he retreats and grooms himself, but is soon back down and all over the sticks. Katie interprets his body language – “Best. Day. Ever.”
Video caption: Ring-tailed lemur Tugger shows a definite interest in the two outer sticks that have been marked with female odors.
Duke Lemur Center Volunteer