Pollinator attraction in the Ficus deltoidea complex: Varietal specificity in a fig wasp that likes to stay close to home

Abstract

Species boundaries are maintained by limitations on gene flow between taxa. In flowering plants pollinator specificity can strongly influence gene flow patterns and facilitate speciation. Fig trees are species rich and ecologically significant plants. It was once believed that each species had its own unique pollinator fig wasp, but numerous exceptions are now known. The dioecious Ficus deltoidea complex is distributed across southern South-East Asia with 13 recognised varieties of uncertain status, seven of which are found in Peninsular Malaysia. We investigated the host preferences of one of their Blastophaga pollinators, reared from the epiphytic F. deltoidea var. angustifolia. Our series of experimental manipulations using free-flying fig wasps and figs on host trees showed that male figs were preferred, that only their natal variety was attractive and that pollinators only dispersed from their natal trees if no suitable figs were present there. Fig wasps can only reproduce in male hosts, so preferred entry to male figs has clear advantages for them, as does their reluctance to disperse from natal trees. This behaviour is likely to reduce seed set on female plants, with potential consequences for host population dynamics. The extreme specificity of the Blastophaga sp. suggests gene flow between varieties of F. deltoidea is low or absent and that different varieties may be different biological species.