Live fast, die young: flexibility of life history traits in the fat-tailed dwarf lemur (Cheirogaleus medius)

The fat-tailed dwarf lemur, Cheirogaleus medius, occurs in ecologically very different habitat types (rainforest and dry forest) across Madagascar. Its extraordinary biological characteristics, such as monogamy and long-term hibernation, allow us to investigate behavioral, ecological, and physiological flexibility of this species in populations across different ecological environments. This study aims to determine whether different life history and physiological traits show variation in adaptation to the differing ambient conditions or are conservative and influenced more by the organism's evolutionary history. We compared body masses, life history traits, social organization, and hibernation duration of two populations of C. medius, one from a littoral rainforest and one from the dry deciduous forest. We revealed clear geographical differences in the length of hibernation duration as well as, more surprisingly, in life history traits. We found that this species' reproductive strategies seem to be highly flexible. Animals in the rainforest can spend more time in the active state due to a shorter hibernation period, but have, in general, a shorter life expectancy due to higher mortality rates. Hence, they seem to maximize their total reproductive output with higher reproductive rates (larger litter sizes, greater number of litters). Home ranges and social organization, on the other hand, did not vary between habitats, suggesting that the general requirements of this species are independent of environmental conditions. In conclusion, some life history traits, formerly assumed to be genetically fixed parameters of primate species, prove in fact to be highly flexible. Different populations of the same species show distinct adaptations according to the prevailing conditions in order to maximize individual reproductive output.