Social life-history response to individual immune challenge of workers of Bombus terrestris: a possible new cooperative phenomen

Solitary organisms can minimise fitness loss from parasitism with a facultative change to an earlier reproduction. Such a shift of the reproductive effort gives the host a chance to compensate for the cost on future reproduction resulting from the infection. In the case of social insects, where brood care and reproductive effort are shared between the queen and her workers, adjustments of the reproductive effort would depend on collective decision-making.

In the February issue of Ecology Letters, Moret and Schmid-Hempel at the Swiss Federal Institute of Technology of Zurich, report a study that tested for this possibility by experimentally activating the immune response of individual workers in colonies of the bumblebee Bombus terrestris. This induction resulted, in combination with environmental conditions, in a reduction of fitness of the social unity and a collective response towards earlier reproduction. As both phenomena are expressed at the level of the colony, the result suggests that key elements of the use of immune defence have been maintained through the evolutionary transition to sociality.