IntroductionMaternal kin selection is a driving force in the evolution of mammalian social complexity and it requires that kin are distinctive from nonkin. The transition from the ancestral state of asociality to the derived state of complex social groups is thought to have occurred via solitary foraging, in which individuals forage alone, but, unlike the asocial ancestors, maintain dispersed social networks via scent-marks and vocalizations. We hypothesize that matrilineal signatures in vocalizations were an important part of these networks. We used the solitary foraging gray mouse lemur (Microcebus murinus) as a model for ancestral solitary foragers and tested for matrilineal signatures in their calls, thus investigating whether such signatures are already present in solitary foragers and could have facilitated the kin selection thought to have driven the evolution of increased social complexity in mammals. Because agonism can be very costly, selection for matrilineal signatures in agonistic calls should help reduce agonism between unfamiliar matrilineal kin. We conducted this study on a well-studied population of wild mouse lemurs at Ankarafantsika National Park, Madagascar. We determined pairwise relatedness using seven microsatellite loci, matrilineal relatedness by sequencing the mitrochondrial D-loop, and sleeping group associations using radio-telemetry. We recorded agonistic calls during controlled social encounters and conducted a multi-parametric acoustic analysis to determine the spectral and temporal structure of the agonistic calls. We measured 10 calls for each of 16 females from six different matrilineal kin groups.ResultsCalls were assigned to their matriline at a rate significantly higher than chance (pDFA: correct = 47.1%, chance = 26.7%, p = 0.03). There was a statistical trend for a negative correlation between acoustic distance and relatedness (Mantel Test: g = -1.61, Z = 4.61, r = -0.13, p = 0.058).ConclusionsMouse lemur agonistic calls are moderately distinctive by matriline. Because sleeping groups consisted of close maternal kin, both genetics and social learning may have generated these acoustic signatures. As mouse lemurs are models for solitary foragers, we recommend further studies testing whether the lemurs use these calls to recognize kin. This would enable further modeling of how kin recognition in ancestral species could have shaped the evolution of complex sociality.

Frequent kin-biased coalitionary behaviour is a hallmark of mammalian social complexity. Furthermore, selection to understand complex social dynamics is believed to underlie the co-evolution of social complexity and large brains. Vocalisations have been shown to be an important mechanism with which large-brained mammals living in complex social groups recognise and recruit kin for coalitionary support during agonistic conflicts. We test whether kin recognition via agonistic calls occurs in a small-brained solitary foraging primate living in a dispersed social network, the grey mouse lemur (Microcebus murinus, Miller JF, 1777). As mouse lemurs are frequent models for ancestral solitary foraging mammals, this study examines whether kin recognition via agonistic calls could be the foundation from which more complex, kin-based coalitionary behaviour evolved. We test whether female wild mouse lemurs in Ankarafantsika National Park, Madagascar, react differently to agonistic calls from kin and nonkin and to calls from familiar and unfamiliar individuals during playback experiments. Subjects showed no significant differences in reactions to the different stimuli; thus they did not react differently based upon kinship or familiarity. Results suggest that this solitary foraging species does not use agonistic calls to recognise kin and monitor agonistic interactions involving kin, unlike several species of Old World monkeys and hyenas. Thus, kin recognition via agonistic calls may have evolved independently in these lineages in parallel with greater social complexity and frequent coalitionary behaviour.