|Research shows it is easier for female ruffed lemurs to raise their young using a system of communal nesting and crèches. |
photo: Omika / Fotolia
Communal nesting, where several mothers regularly pool and cooperatively rear offspring, is unusual in mammals. This type of crèching behavior is especially rare among primates, with the notable exceptions of humans, some nocturnal strepsirrhines, and—as we show in this study—black-and-white ruffed lemurs (Varecia variegata). Here, we combine data on nesting behavior, genetic relatedness, and infant survivorship to describe variation in ruffed lemur infant care and to examine the potential benefits of ruffed lemur communal breeding. Reproductive events were rare, and females produced litters (synchronously) only once in 6 years of observation. We show that not all mothers participate in communal crèches, but those that did had greater maternal success; communal breeders spent more time feeding and their offspring were more likely to survive. Although cooperating mothers were often related, females also cooperated with non-kin, and those who shared infant care responsibilities had greater maternal success than mothers who did not participate. If there is indeed a causal link between maternal cooperation and reproductive success, this unusual behavior, like that of human communal rearing, may have evolved via some combination of kin selection and mutualism.
Keywords: Reproductive success, Communal breeding, Crèching behavior, Lemurs, Allomaternal care
|Infant black-and-white ruffed lemur. |
Photo by Andrea Baden.
'Nursery Nests' Are Better for Survival of Young Black-And-White Ruffed Lemurs
— Research shows it is easier for female ruffed lemurs to raise their young using a system of communal nesting and crèches.
Baden and her team studied eight female black-and-white ruffed lemurs (Varecia variegata) in the Ranomafana National Park in Madagascar who only once reproduced large litters during the six consecutive years of observation. Combined data on their nesting behavior, genetic relatedness and the survival of infants showed a positive relationship between crèche-use, a mother’s time spent feeding and infant survival.
Ruffed lemurs are large-bodied and gregarious primates with slow life histories that form social communities to cooperatively help defend territory. They are the only diurnal non-human primates who bear litters of altricial or undeveloped offspring. This means that, as in humans, newborn ruffed lemurs need special care and feeding. Newborns, for instance, cannot yet cling to their mothers at birth, which makes travel together in the forest canopy impossible. This places a specific energy burden on the mother, who provides exclusive care for the first six weeks of her infants’ lives and therefore has less time to spend on feeding and foraging.
Only a small percentage of female ruffed lemurs opt for solitary brooding and raise their young on their own. The others participate in communal nesting, breeding and babysitting in which several mothers regularly pool resources to cooperatively rear their offspring until they are about 10 weeks of age and are capable of independent travel. This method of infant care is unusual in mammals, and especially among primates, with the most notable exceptions being humans and some nocturnal primates of the suborder Strepsirrhini.
|Black-and-white ruffed lemur Varecia variegata variegata in a tree. |
photo: Tony CAMACHO/SCIENCE PHOTO LIBRARY
Communal nesting allowed female ruffed lemurs to spend less time at their nests and gave them more opportunity to feed elsewhere than was possible for single nesting females. Infant survival was also significantly higher the more this crèche system was used. Genetic tests showed that cooperation was common among kin, but not exclusively so. This is the same as with humans and several other communally breeding birds and mammals.
“Kinship may have helped the evolution of cooperative breeding in primates, but the mutual benefits may outweigh the costs of helping, irrespective of any family relationships,” says Baden, who believes that the current research sheds light on understanding just how communal breeding evolved. “Our results contribute to a growing body of evidence suggesting that kin selection alone cannot explain the extensive cooperation observed in many animal taxa.”
Baden A.L., Wright, P.C., Louis E.L., Bradley B.J. 2013. Communal Nesting, Kinship, and Maternal Duccess in a Social Primate. Behavioral Ecology and Sociobiology.