Data for Reproductive females of a cooperatively breeding rodent are in better body condition when living in large groups

Cooperation and group living has been suggested to facilitate survival in varying environments and under challenging conditions. However, group living may also be associated with costs, particularly in species where individuals within groups may compete for limited resources. How the costs and benefits of cooperative group living affect cooperative breeding mammals in varying environments is still unclear. Here, we use data collected from wild cooperatively breeding Natal mole-rats (<i>Cryptomys hottentotus natalensis</i>) living in a seasonally varying environment to assess if body condition changes between seasons and whether these changes are contingent on group size. We show that the body condition of reproductive females improved with helper number during both the benign summer and the harsher winter season. However, body condition of other group members showed little dependency on group size or season. Only when including one extremely large group did body condition of non-breeders weakly, albeit significantly, change depending on group size and seasonality. These results suggest that large group sizes may yield minor benefits to non-breeding group members during winter and may invoke some costs during summer. Group living in Natal mole-rats is likely promoted by a combination of collective foraging, thermoregulatory benefits and potentially indirect fitness benefits through improved body condition of the breeding female.