Direct evidence for the cycling of fig wasps within one male fig tree

Abstract

Fig wasps can only survive when flowering fig trees are present all the year around. Ficus trees can only reproduce if they are pollinated by highly specific wasps. In highly seasonal habitats, when only few trees occur at a specific site, gaps in fruiting may lead to the extinction of the local pollinator population. This paper demonstrates that in a dioecious fig tree, Ficus hirta, the fig wasp population can be maintained successfully within an individual plant, through the strong intra-tree asynchrony in flowering. By experimentally bagging trees, we showed that the pollinating wasps (Blastophaga javana hilli) could live for two generations, and the non-pollinating wasps (Sycoscapter sp.) for up to three generations in a closed intra-tree system. However, there was a sharp decline in wasp abundance, deviating sex ratios and decreasing flower occupancy before their ultimate extinction, indicating that the wasp populations were not sustainable. This phenological strategy may enable dioecious figs, which are not constrained by the cost of selfing, to occupy a wider breadth of niches in both tropical and seasonal habitats.