Promiscuity (...Hierarchical?)

According to Verna Case, 2004, hierarchical promiscuity occurs when there are strict dominance hierarchies among males and the males compete via contest competition for rank, which in turn allows them access to estrous females. Females will chose the highest ranking male to mate with, ensuring good genes for her offspring. This type of promiscuity often occurs when females are found in groups too large for one male to control, and multiple males associate with female groups to compete for mating rights. Dominant males use aggression to control females during estrous, and subordinate males may form coalitions to obtain mating rights.

Ring-tailed lemurs are promiscuous (Jolly 1988), though whether or not it is hierarchical promiscuity can be debated. Males compete fiercely for mates due to the very short breeding season (it is believed that this fierce, seasonal competition has allowed female dominance to prevail since males must conserve their energy throughout the rest of the year). During the breeding season, males engage in viscious fights that include biting, slashing and stink fighting around an estrous female (Jolly 1985, Haring, 2004). Males from many groups have been shown to temporarily move into one another's home ranges in attempts to gain extragroup mating opportunities (Gould and Overdorff 2001). While males keep up a year-round hierarchy of threats resulting in a loose, constantly changing dominance hierarchy, the winner of the viscious fights for a female has often been found to be a subordinate male (Jolly 1985). As long as the female stays in the center of the troop, the males will continue to fight; however, if she decides to move away from the center of competition, the male best able to fend off competitors can follow her until they are alone. Sometimes, this can disrupt the established dominance hierarchy (Jolly 1988). Thus, the constant threat hierarchy has little to do with sex priority (Jolly 1985), and high-ranking males do not necessarily have first mating advantage (Miller 2002). Therefore, promiscuity in ring-tailed lemurs is complex and is not necessarily strictly hierarchical. However, for the purpose of this study I would say that ring-tailed lemurs do engange in hierarchical promiscuity. Males do form dominance hierarchies and they do compete for mating rights; while the two may not always be related, these forms of male competition make "hierarchical" the most convenient label to put on ring-tailed lemur promiscuity.

Food resources, though scattered and clumped, are relatively abundant for ring-tailed lemur troops; therefore large amounts of animals can afford to be together at the same time. In this sense, it would not make sense to be monogamous, since the large home range is not defensible by just one pair of lemurs. Also, the troop is constantly moving long distances to find food, so it is advantageous to be in a large group. Being in a large group where males and females encounter each other frequently makes promiscuity easy and convenient.

Female ring-tailed lemurs can afford to be dominant and promiscuous. Being dominant, one might think that it would be advantageous for females to force a male into a monogamous relationship. However, this is not needed and the female actually benefits from promiscuity by mating with the strongest male with the "best" genes. Why is male help (as would be obtained through a monogamous relationship) not necessary? Males are simply not needed for parenting, and in fact have very little to do with the infants. Infants mature very rapidly--by two weeks they are actively moving around and riding on their mothers' backs (initially ride lengthwise under their mothers' bellies like young monkeys and apes, Haring 2004, Jolly 1985). Ring-tail infants will begin to sample solid food after one week and take their first steps away from their mother after 3-4 weeks (Haring 2004). This is considerably early compared to infant maturation in other primate species (Chalmers 1980). Infant mortality during the first year is between 30% and 50% (Anderson, 2004). Due to the typical ring-tailed lemur habitat of dry, seasonal scrub, infants much reach weaning quickly before the summer food supply runs out (Jolly 1985). Because of the rapid development in infants, male parenting is not needed and females can forage and move fairly easily with their infants. Also, because of the scarcity of predators in Madagascar, females and infants do not need male protection. Infants grow up surrounded by a community of mothers and aunts, and female lemurs will groom each other's offspring (Jolly 1988). This is further indication that male parenting is not needed and is a result of all the females in a troop being related (see Kin Selection?).

Seasonality of Reproduction and Troop Life

Allison Jolly (1988) describes the seasonality of ring-tailed lemur life. The seasonal breeding cycle in ring-tailed lemurs leaves the females pregnant and lactating during the harshest months. They mate during April and will give birth during August or September (Anderson, 2004). In southern Madagascar, July is dry and cold, and many young lemurs (along with Malagasy children) catch bronchities and die of pneumonia. September is very dusty and hot, and many deciduous trees lose their leaves. Pregnant ringtails will lick dew from bare branches at dawn, at noon they will drape themselves, panting, in the trees, and at dusk they will sometimes drink from a stream, always alert for predators. Only in the dark, when it is cool, do the mothers give birth. Males grow scrawny during this time, and welcomed relief comes in October, when trees begin to flower and fruit (in time to produce seeds for November rains). During this time the troop eats plentifully and males will regain strength and begin to wander, until up to a quarter or third have switched troops. They feed and fatten up, engaging in "fight-training" for the next breeding season as they feud with members of their new group.