Variation in social dominance in six mouse lemurs across an ecological gradient in northwestern of Madagascar

Social dominance and rank have been shown to influence the social relationships formed by individuals of many species and may regulate the access to limited resources in times of low resource availability. It remains a controversial subject in how far dominance patterns vary between closely related species and in how far they are influenced by ecological and biological factors, such as forest type and reproductive activity. We investigate some sources of variation in social dominance developing in male-male and male-female dyads in a nocturnal primate radiation, the Malagasy mouse lemurs (Microcebus spp.). We explored the patterns of inter-(male-female) and intra-sexual (male-male) interactions among six closely related mouse lemur species, at six sites in northwestern Madagascar using a standardized social encounter paradigm. Six intra- and six intersexual pairs were being observed per species, each for 3h at the beginning of their activity period, over six consecutive days (18h in total). Direct observations were conducted with all agonistic behaviors of both pair partners being recorded whenever they occurred. Dominance was determined by comparing the number of decided conflicts between the dyad partners. Male-female dyads of the six species differed significantly in the frequency of agonistic behaviors. Results suggest 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. Variations in aggression rates between male-male dyads could be influenced by differences in forest type and/orin reproductive state. Only one (M. mamiratra) out of five species showed signals of unambiguous female dominance in all male-female dyads. The study confirms a higher degree of social plasticity between species than previously expected in these small solitary foragers and its requires further scientific attention.