Reconciliation and post-conflict behaviour in ringtailed lemurs, Lemur catta and redfronted lemurs, Eulemur fulvus rufus

Sociality always entails some form of intra-group competition for food or other limited resources and so increases the probability of conflict between individuals. Within groups, non-dispersive modes of coping with competition and its consequences may evolve. External factors, such as predation risks or the ability to defend resources against other groups may select for the same outcome. The study of Lemuriformes can provide such comparative date. Lemurs form an independent primate radiation and represent the most primitive group-living primates. Also, their social complexity and other aspects of their social structure differ from most anthropoid primates.

 

Two ring-tailed lemurs showing aggresion toward one another.

Two ring-tailed lemurs and two red-fronted lemurs that have occupied large natural-habitat enclosures at Duke University for several years were used at subjects for this study. Their daily diet is supplemented by fruit or monkey chow, along with their natural foods they eat. They are used to humans observing them, and are each individually identified by special neck collars. The fence that separated the two species groups was removed, and the resulted deaths and animal removals for L. catta was between 12 and 26, and for E. fulvus between 5 and 11. The victims were all ages and sex classes.

For the observations, the lemurs were characterized as only aggressive (A), only submissive (S), both aggressive and submissive (AS), or no agonistic behavior (O). First recorded was several details of each agonistic interaction, second recorded was the intensity of each conflict, using a simple scale of 1 to 5 (1 being low and 5 being high). Lastly recorded was the identity of the individuals.

Red-Fronted Lemurs

Agonistic interactions may affect the absolute frequency of subsequent interactions, their relative timing, or both. Several methods for demonstrating reconciliation are available, the most common employing a specific matched-control period, usually the same time on the following day for each post-conflict period. One can determine whether affinitive contact occurred earlier or exclusively in the post-conflict period, compared to the respective matched-control period. The following were the results of the conflicts.

 

In the matter of L. catta, the results indicate that only 9 of the 125 conflicts were followed by at least one affinitive interaction between former opponents. Contrastingly, affinitive interactions between former adversaries were observed in 15 of the 125 recorded. These results indicate that there is a strong trend toward a decreased possibility of affinitive contact between former opponents after a conflict. For E. fulvus, agonistic interactions between them had a more positive effect, and had a significant effect on subsequent behavior because of affinitive interactions between former opponents occurred significantly earlier following a conflict. The following table indicates the number of opponents who reconciled.


The most important conclusion of this study is the lack of evidence for an increase in post-conflict affinitive interaction between former opponents in ringtailed lemurs. Also, the reconciled hierarchy model does not provide a general explanation for the occurrence of reconciliation across species. Reconciliation is not a necessary condition for life in permanent social groups.

      Kappeler, P. (1993) Reconciliation and post-conflict behaviour in ringtailed lemurs, Lemur catta and redfronted lemurs, Eulemur fulvus rufus. Animal Behaviour Volume 45, Issue 5, Pages 901-915

Group histories and offspring sex ratios in ringtailed lemurs

Statistically significant departures from 50:50 birth sex ratios have been reported for a variety of mammals. General explanations for these deviations are usually based on differences  in the net benefits of producing sons versus daughters, depending on attributes of individual mothers or their populations.

There are four separate hypothesis to understand this, the first being the Trivers-Willard (T-W). It focuses on male intrasexual competition. The effects are anticipated when offspring of a given sex in superior physical condition have greater reproductive potential than offspringof the other sex in a similarly augmented condition, or females can influence the physical condition of offspring at maturity. A second hypothesis, local resource competition (LRC), applies to situations in which one sex is philopatric and so faces competition mainly from philopatric individuals. When LRC increases, females are predicted to produce a greater number of the dispersing sex to mitigate local competition. This LRC effect is

an attribute of the population or group and so is not expected to vary among individuals. The third hypothesis also involves competition among members of the philopatric sex. the relative advantages of producing sons versus daughters vary among mothers within groups, and so we call this hypothesis LRC-individual. Under LRC-individual, only high-ranking females bias production toward the philopatric sex because they can best support these offspring, usually daughters, against harassment from likesexed individuals. A fourth hypothesis concerns delayed benefits that may arise from producing the philopatric sex. This local resource enhancement hypothesis (LRE) proposes that when one sex effectively “repays” costs of reproduction by providing benefits to the mother, this sex should be overproduced under appropriate conditions.

These four hypotheses were tested on Lemur catta, at Duke University. Intra- and intergroup competition is intense for female ringtailed lemurs, suggesting that factors associated with both LRC and LRE are important. However, maternal agonistic intervention is irregular and matrilineal rank inheritance unreliable in ringtailed lemurs, predicting that LRC effects will be observed predominantly at the population level. Competition patterns vary across wild populations of ringtailed lemurs, and so the factors that influence sex ratios may also vary. Male intrasexual competition is intense, and a male’s physical condition should aid him in this competition. If adjustment of offspring sex ratios is an adaptive element of female life histories, individual females are expected to respond facultatively to varying circumstances, perhaps as part of an adaptive norm of reaction.

Two social groups (Lc1 and Lc2) ranged semi-freely inlarge forested natural habitat enclosures. Both
indoor and outdoor groups have experienced a range of demographic conditions, particularly with respect to the composition of the groups and their stability. Males have transferred freely between the two groups and females have defended stable territorial boundaries without obstruction. Evicted females have been removed from the enclosures by Duke University. Animals in the natural habitat enclosures foraged extensively on the natural vegetation while also receiving daily provisions. The following information was obtained from the records for each birth: infant sex, mother’s location, her age, and the number of mature females and mature daughters present in the group at the likely time of conception. Ringtailed lemurs are highly seasonal in their reproduction, with conceptions occurring in the fall mating season and births the following spring.

In the LRC-population results, species with male dispersal predicts a polutaion leve male bias in the secondary sex ratio. Even though the ratio was slightly biased toward males, it was not statistically different from an equal sex ratio. LRC-population also predicts that mothers overproduce sons when groups are large, as males eventually disperse and will not compete for limited resources. Females in large natural habitat enclosure groups tended to overproduce sons. For the T-W results, mothers

that lose an infant early in the birth season are predicted to produce sons in the next birth season, as they are expected to have more energy available for investing in this next infant. The percentage of twins was slightly higher among females that were recorded as having lost an infant. The sex ratio of infants born to these females, however, was not significantly different from equality with a binomial test. As for the LRE, top-ranking females overproduced daughters when resources were maximal provides indirect support for
LRE modified by LRC. LRE makes two more direct predictions for ringtailed lemurs.

Female with offspring.

     Pereria, M. and Nunn, C. (1999), Group histories and offspring sex ratios in ringtailed lemurs ( Lemur catta ). Behavioral Ecology and Sociology, vol 48.1.



Mating Season Aggression and Fecal Testosterone Levels in Male Ring-Tailed Lemurs (Lemur catta)

Ring-Tailed Lemurs are diurnal, polygamous, and the female is only sexually receptive about 1 day a year. There is female social dominance over males, and the males do not care for the offspring.

The lemurs in this study are in an enclosed area, 9 hectares, and have been there for many years previous to the study. During the study, the ring-tails were also involved in a protocol that involved luring them into holding cages within the forest enclosure on a biweekly basis to collect blood samples and morphological measures.

During mating, different aggressive and submissive acts were recorded. Aggressive acts included

bite, lunge, chase, cuff, and grab. Submissive acts included jump away, flee, cower, and a high-pitch submissive vocalization, spat call, known to be the formal signal of subordination in this species. This was mostly between females. Males tendency to perform these actions correlated with sexual behavior, and their proximity to females.

"Look, I'm a big lemur because I stand taller than you!"

Their sexual behavior correlated directly with preestrus, estrus, and postestrus. Comparison of Serum and Fecal Testosterone Fecal testosterone level correlated significantly and positively with serum testosterone level among 9 adult ring-tailed males. Among 10 males, mean fecal testosterone levels increased significantly from the premating (October) to the mating period (December). Prior to the mating season the correlation between testosterone level and rate of aggression was not statistically significant, whereas during the mating season the correlation was positive and significant.

For most studies, fewer data allow for greater error in measurement and therefore reduced chances of

demonstrating significant correlations. Comparability of results from ring-tailed lemurs maybe due to the fact that mating system dynamics in this species resemble those of many nonmonogamous birds.

Cavigelli, S. and Pereira M. (2000), Mating Season Aggression and Fecal Testosterone Levels in Male Ring-Tailed Lemurs (Lemur catta). Hormones and Behavior, 37 no. 3. 246-255