Stingless bees and their adaptations to extreme environments.

Nearly half of all terrestrial tropical ecosystems around the globe comprise dry forests, characterised through elevated temperatures all year round, and short rainy seasons at irregular intervals. The consequent water deficit over several consecutive months limits the availability of floral resources to often very brief and unpredictable periods, which poses a challenge to the maintenance of perennial colonies in highly eusocial bees. Thus, only few highly eusocial bees occur permanently in tropical dry forests, among them some highly adapted species of stingless bees (Apidae, Meliponini). In the present review, we discuss the current knowledge on the adaptations to such extreme environments in Melipona subnitida, a stingless bee native to the Brazilian tropical dry forest. Key to the success of this species is not so much heat resistance of foragers, as it is the ability to maintain perennial colonies despite extended dearth periods. After several months of drought, M. subnitida colonies are capable of re-establishing fully functional colonies from nests containing only few dozens of workers. This surprising resilience is based on a quick reaction to precipitation-driven increase in floral resource availability, mainly owing to selective foraging at high-profit resources and an immediate up-regulation of brood production once food storage conditions improve.