Functional morphology of the metapleural gland in the leaf-cutting ant Acromyrmex octospinosus

The metapleural gland is unique for ants and its main function is the produ ction of antibiotics. The gland is considered to be of particular significa nce in leaf-cutting ants, which need to protect both themselves and their c lonally reproducing fungal symbiont from pathogens and microbial competitor s. In a detailed study of the histology of the metapleural gland of the lea f-cutting ant Acromyrmex octospinosus the diameter of the storage room (bul la) is shown to be highly positively correlated (r = 0.84) with the number of secretory cells inside the gland. This justifies the use of the easily o btainable bulla diameter as an approximation of the size of the actual meta pleural gland in e.g. studies of gland allometry. Histological cross sectio ns also show that contraction of the rather massive thoracic muscles may le ad to compression of the collection chamber of the metapleural gland and ma y thus allow active enhancement of the flow of gland secretion to the reser voir behind the bulla.