The Extent of Pollinator Sharing Among Fig Trees in Southern China

Abstract

\n Background: The obligate mutualism between fig trees (Ficus, Moraceae) and pollinating fig wasps (Agaonidae) is a model system for studying co-evolution due to its perceived extreme specificity, but recent studies have reported a number of examples of trees pollinated by more than one fig wasp or sharing pollinators with other trees. This makes pollen flow between species and hybridization more likely. We reared pollinator fig wasps from figs of 13 Chinese fig tree species trees and established their identity using genetic methods in order to investigate the extent to which are they were supporting more than one species of pollinator.Results: Our results showed 1) pollinator sharing was frequent among closely-related dioecious species (where pollinator offspring and seeds develop on different trees), but not monoecious species and 2) that where two pollinator species were developing in figs of one host species there was usually one fig wasp that was far rarer than the other. An exception was F. triloba, where its two pollinators were equally abundant. Conclusions: Our results suggest that host expansion events where pollinators reproduce in figs other than those of their usual hosts are not uncommon among fig wasps associated with dioecious hosts. Because closely related trees typically have closely related pollinators that have a very similar appearance, the extent of pollinator-sharing has probably been underestimated. Any pollinators that enter female figs carrying heterospecific pollen could potentially generate hybrid seed, and the extent of hybridization and its significance may also have been underestimated.