Abstract:
In many animal societies where hierarchies govern access to reproduction, the social rank of
individuals is related to their age and weight and slow-growing animals may lose their
place in breeding queues to younger ‘challengers’ who grow faster than they do. The
threat of being displaced may be expected to favour the evolution of competitive growth
strategies, where individuals increase their own rate of growth in response to increases in the
growth of potential rivals. While growth rates have been shown to vary in relation to
changes in the social environment in several vertebrates including social fish and
mammals, it is not yet known whether individuals increase their growth rates in response to
increases in the growth of particular reproductive rivals. Here we show that, in wild Kalahari
meerkats (Suricata suricatta), subordinates of both sexes respond to experimentally induced
increases in the growth of same-sex rivals by raising their own growth rate and food intake.
In addition, when individuals acquire dominant status, they show a secondary period of
accelerated growth whose magnitude increases if the difference between their own weight
and that of the heaviest subordinate of the same sex in their group is small. Our results show
that individuals adjust their growth to the size of their closest competitor and raise the
possibility that similar plastic responses to the risk of competition may occur in other social
mammals, including domestic animals and primates.
