Mutually beneficial interactions between two different species are of fundamental ecological importance. Most plants and animals are dependent on cooperative symbionts, yet it is poorly known what constrains symbionts from turning into parasites. What prevents one partner from reaping the benefits of the interaction without paying the costs? Such cheaters would threaten to break down the mutualism. Recent studies of mutualistic systems have documented host sanctions that might prevent cheating by lowering the fitness of uncooperative symbionts. However, it has rarely been demonstrated that sanctions are sufficient to prevent the spread of parasitism among mutualists. This project will study sanctioning by fig trees and possible cheating by their pollinating fig wasps. Fig trees can produce viable seeds only after being pollinated by fig wasps, and fig wasps can reproduce only by laying their eggs in fig flowers. Fig wasps either do or do not carry pollen, and pollen-free wasps are more common in the fig species with the weakest sanctions. Surveys, manipulative field experiments, and molecular tools will be used to determine whether the observed host sanctions can prevent pollen-free wasps from spreading in a population.
The proposed research will provide important and novel information broadly applicable to the evolution and maintenance of mutualistic systems in general. Increased understanding of how mutualisms are maintained will aid our understanding also of how symbionts in our bodies and in agricultural systems can be prevented from turning parasitic.
