Colony size predicts division of labour in Attine ants

Division of labour is central to the ecological success of eusocial insects, yet the
evolutionary factors driving increases in complexity in division of labour are
little known. The size–complexity hypothesis proposes that, as larger colonies
evolve, both non-reproductive and reproductive division of labour become
more complex as workers and queens act to maximize inclusive fitness.
Using a statistically robust phylogenetic comparative analysis of social and
environmental traits of species within the ant tribe Attini, we show that
colony size is positively related to both non-reproductive (worker size variation)
and reproductive (queen–worker dimorphism) division of labour.
The results also suggested that colony size acts on non-reproductive and reproductive division of labour in different ways. Environmental factors, including
measures of variation in temperature and precipitation, had no significant
effects on any division of labour measure or colony size. Overall, these results
support the size–complexity hypothesis for the evolution of social complexity
and division of labour in eusocial insects. Determining the evolutionary
drivers of colony size may help contribute to our understanding of the
evolution of social complexity.