Precision of host sanctions in the fig tree-fig wasp mutualism: consequences for uncooperative symbionts

Abstract

Host sanctions that reduce the relative fitness of uncooperative symbionts provide a mechanism that can limit cheating and thus stabilise mutualisms over evolutionary timescales. Sanctions have been demonstrated empirically in several mutualisms. However, if multiple individual symbionts interact with each host, the precision with which individual cheating symbionts are targeted by host sanctions is critical to their short- and long-term effectiveness. No previous empirical study has directly addressed this issue. Here, we report the precision of host sanctions in the mutualism between fig trees and their pollinating wasps. Using field experiments and molecular parentage analyses, we show that sanctions in Ficus nymphaeifolia act at the level of entire figs (syconia), not at the level of the individual flowers within. Such fig-level sanctions allow uncooperative wasps, which do not bring pollen, to avoid sanctions in figs to which other wasps bring pollen. We discuss the relevance of sanction precision to other mutualisms.