If bigger is better why bother with the rest: Worker size variation in bumble bees in response to poor resource conditions

Bumble bees workers (Bombus sp.) exhibit a large variation in worker body size, with up to a ten fold weight difference between full genetic sisters. Unlike some of the highly developed morphological castes in ants, there appears to be little adaptive benefit for producing variation in workers, as smaller workers are worse at performing colony tasks. However, smaller workers can survive starvation for longer than their larger sisters and represent a smaller investment in resources. We test the hypothesis that smaller workers are either adaptations to poor resource environments or highly variable resource environments. By raising colonies in the lab of different resource regimes we find that colonies in poor resource treatments show decreased average body size, but there appears to be no tradeoff in producing either larger or more workers. Larger workers are still produced, indicating their importance to colony function even under adverse conditions.