Eusociality describes a system in which many animals (mostly insects) live, whereby some individuals forego the opportunity to reproduce in order undertake various tasks of benefit to the group, such as helping to raise and care for other (generally related) offspring. From an evolutionary perspective, this represents an interesting paradigm; by investing in related young, fitness benefits are received at the genetic level – the higher the benefits and more closely related kin, the higher the reward in evolutionary terms. One such eusocial species is the sweat bee (Halictus scabiosae). These insects are primitively eusocial, and retain the ability to breed independently, meaning that they are very useful to the study of the origins of eusociality.
Female sweat bee offspring in the first brood generally develop to be smaller and become workers, helping their mother to rear a second brood of males, and gynes which will go on to grow larger and become founders of new nest sites. This trend indicates that there is a process occurring during development which causes first brood females to become workers, rather than growing large enough to overwinter and establish a new nest of their own.
A recent study, published today in Frontiers in Zoology suggests that the queen bee may manipulate food allocation to her daughters, meaning they are smaller in size and thus channelling them into a worker role. The study authors Nayuta Brand and Michel Chapuisat, both at the University of Lausanne, find that females in the first brood receive significantly smaller provisions of pollen during development in comparison to the second brood. Furthermore, there is no difference seen in the size of first brood males in comparison to second brood males, indicating that the queen bee is ‘choosing’ to feed her daughters less.
Dr Chapuisat explained, “Although it is hard to distinguish parental manipulation from resource availability and resource acquisition, which are influenced by vegetation, weather, seasonal variation, numbers of foragers and more, the fact that we were able to see that first brood female body size remained constant despite pronounced differences in weather strengthens our argument that the foundresses restrict the food of their daughters to drive them into the worker role.”