The ecological and evolutionary importance of nectar-secreting galls

Abstract

Some species of cynipid wasp engage in mutualisms with ants by producing nectar-secreting galls, providing carbohydrates, and receiving protection from parasitoids. The galls are functionally similar to extrafloral nectaries, plant structures well known for their role in ant–plant mutualisms. Though not well known, nectar-secreting galls may have important ecological and evolutionary implications for arthropods, plants, and the evolution of ant-mutualisms. Here, I review the known ecology of nectar-secreting galls and speculate on their wider ecological significance based on past research and similar ecological systems. I then develop a conceptual framework for considering the possible historical role of nectar-secreting galls in the evolution of ant-mutualisms. I review current knowledge on the origin of ant-mutualisms and develop a hypothesis for the role of nectar-secreting galls using examples of similar, contemporary species interactions. Finally, I lay out some of the future directions for research into nectar-secreting galls and their species interactions, including important questions that remain to be addressed. Future studies of the diversity and ecology of nectar-secreting galls are necessary to determine the extent to which they may be involved in ecological functioning and the evolution of ant-mutualisms, and it is hoped that this review will contribute to motivating and developing future research.