Sources of variation in social tolerance in mouse lemurs (Microcebus spp.)

Social tolerance strongly influences the patterns of affiliation and aggression in animal societies. However, not much is known about the variation of social tolerance in species living in dispersed social systems that combine solitary foraging activities with the need of coordinating social interactions with conspecifics on a regular basis. This study aims to investigate the sources of variation in social tolerance within a Malagasy primate radiation with dispersed social systems, the mouse lemurs (Microcebus spp.). Six mouse lemur species were selected as model species that belong to three different taxonomic clades, live in two types of forest environments (dry and humid), and differed in this study with respect to their reproductive activity. Six male-female and six male-male dyads of each species were tested temporarily in a standardized social encounter paradigm in Madagascar to collect data on joint use of space, non-agonistic body contacts, aggression rates, the number of conflicts and the establishment of intra- and intersexual dominance.

Male-female dyads of the six species differed significantly in the frequency of affiliative and agonistic behaviors. In contrast, the variations between male-male dyads could not be explained by one parameter only, but clade membership, forest type, reproductive state as well as species were all suggested to be partially influential. Only one species (Microcebus mamiratra) showed signals of unambiguous female dominance in all male-female dyads, whereas the others had no or only a few dyads with female dominance.

Variations in social tolerance and its consequences are most likely influenced by two factors, ecology (via forest type) and physiology (via reproductive activity), and only to a lesser extent by clade membership. The study suggests that mouse lemur females have higher aggression rates and more agonistic conflicts with males when females in the population are reproducing, at least in resource-rich humid forests. The study confirms a high degree of social plasticity between species in these small solitary foragers that supports their taxonomic distinctiveness and requires further scientific attention.