Revisiting the components of Macroscelidea social systems: Evidence for variable social organization, including pair-living, but not for a monogamous mating system

Abstract

Elephant-shrews (Macroscelidea) have long been considered the only mammalian order to be completely monogamous, based on observations of their pair-living social organization. We reviewed primary studies on the four components of social systems (social organization, mating system, social structure, and care system) in elephant-shrews to evaluate whether they truly are monogamous. To identify gaps in our knowledge of their social system, we reviewed evidence for a pair-living social organization, mate fidelity (mating system), pair bonds (social structure), and biparental care (care system). Field data were available for eight species and seven were often pair-living. However, these seven species exhibited intra-specific variation in social organization; two of these species were also solitary living, two species were also group-living, and the remaining three species were both solitary and group-living. The eighth species was exclusively solitary. We reconstructed the ancestral social organization of Macroscelidea using Bayesian phylogenetic mixed-effects models and found that variable social organization, rather than exclusive pair-living, was the most likely ancestral state, though there was high uncertainty. No socio-ecological factors (body size, population density, and habitat) predicted a specific social organization. Observations of mating have been rare, such that no firm statements can be made. However, one unpublished study indicated high levels of extra-pair paternity. Regarding social structure, there was no evidence of pair-bonding, but there was evidence of mate guarding. Only maternal care has been observed, with females having very short nursing bouts. Evidence suggests that despite having often a pair-living form of social organization, Macroscelidea should not be described as a monogamous order, as little or no evidence supports that designation, nor are they exclusively pair-living (social organization) and we urge further field studies on Macroscelidea social systems.