Abstract:
In some eusocial insect societies, adaptation to the division of labour results in multimodal size
variation among workers. It has been suggested that variation in size and growth among nonbreeders
in naked and Damaraland mole-rats may similarly reflect functional divergence associated
with different cooperative tasks. However, it is unclear whether individual growth rates are
multimodally distributed (as would be expected if variation in growth is associated with
specialisation for different tasks) or whether variation in growth is unimodally distributed, and is
related to differences in the social and physical environment (as would be predicted if there are
individual differences in growth but no discrete differences in developmental pathways). Here we
show that growth trajectories of non-breeding Damaraland mole-rats vary widely, and that their
distribution is unimodal, contrary to the suggestion that variation in growth is the result of
differentiation into discrete castes. Though there is no evidence of discrete variation in growth,
social factors appear to exert important effects on growth rates and age-specific size, which are both
reduced in large social groups.
