Abstract:

Mutualism is one of the most important ecological interactions, with strong influences on almost all levels of biological systems. Their long-term persistence raises many challenging evolutionary questions, especially those involving high-level coevolution and coadaptation. Figs and their pollinating wasps are among the most tightly integrated mutualisms known, and provide a model system for developing and testing theories of coevolution. Initial studies suggested specific coevolution between them, described as the famous rule of one fig one wasp. However, more and more exceptions have been revealed by recent studies, and cryptic species in pollinating wasps and host switching were found common in some regions and within some Ficus groups, inducing debates on the levels of species specificity and coevolution. A broad-sense coevolution model to describe the relationship of the related groups of figs and their pollinating wasps was proposed recently. The diverse relationships between figs and their pollinating wasps indicated coexistence of both specific and diffuse coevolution in this mutualism system, producing different species-specificity level. However, which model is the dominant one in this system is still keeping open. The species specificity could be tight or loose in different regions and fig groups involved. Consequently, the frequencies and mechanisms of breakdowns of the one-to-one rule within different fig groups as well as in different regions are essential for the understanding of the relative importance of the competing finer-scale cospeciation or broad-sense co-evolution models.