Abstract:
Selection pressures underpinning the evolution of mammalian sociality and body mass variation have spurred great interest for several decades. Because they inhabit a wide range of geographic localities and habitats, African mole-rat subspecies of Cryptomys hottentotus present a unique opportunity to further our understanding of intra- and interspecific variation of sociality and body mass in mammalian species. We compared the demographics and body masses among 4 C. hottentotus subspecies: the Mahali mole-rat, C. h. mahali; highveld mole-rat, C. h. pretoriae; Natal mole-rat, C. h. natalensis; and common mole-rat, C. h. hottentotus within the context of their respective microclimates and evolutionary history. We propose that all ancestral C. hottentotus subspecies were arid-adapted and thus formed large colonies (as found today in the Mahali mole-rat). However, as the subspecies dispersed to occupy habitats of varying aridity and temperature across South Africa, selection for a particular colony size range in each subspecies arose to provide an adaptive fitness benefit to survive in its habitat. Consequently, the Mahali mole-rat—which remained in a warm and arid environment—retained the largest mean colony size, followed by the Natal mole-rat, which—even though inhabiting a hyper-mesic environment—selected for increased colony sizes to offset the energy requirement of thermoregulation (through huddling) in the cooler montane environments they prefer. The common mole-rat and the highveld mole-rat possessed the smallest mean colony sizes, likely the result of inhabiting a mesic and warm environment. At the same time, body mass variation in the C. hottentotus complex is likely linked to colony size variation, with subspecies having the largest colonies possessing the lowest individual body mass.
