The dynamics of growth in naked mole-rats: the effects of litter order and changes in social structure

Abstract

In this study factors that influence the plasticity in growth and adult body mass in the naked mole-rat (Heterocephalus glaber) are explored. Growth functions (Gompertz transformation) revealed that naked mole-rat pups have the slowest mean maximum growth rate (0.207 g.day⁻¹) of all the Bathyergidae. Growth functions varied significantly between litters and there was an inverse trend between asymptotic body mass and litter order. Similarly, the magnitude of the growth response following the death of the breeding male or older siblings was greater for older litter members. There was a significant correlation between body mass and age at all stages of the colony's history although this relationship weakened with time. It is suggested that dominance interactions between old and young mole-rats within the colony are important factors influencing the growth and reproductive potential of all colony members. Changes in body mass were linked to the behaviour of the individual within the colony providing a mechanism for the apparent match between large body size and colony defence and small body size and work frequency. Despite low genetic variation within colonies there is considerable variation in the size of colony members suggesting that plasticity in growth is the product of different ontogenetic histories of colony members that may serve as the basis for variation in size amongst adults.