The extent of hybridization among recently diverged and sympatric plant species in which reproduction requires specialized pollinators is expected to depend on the fitness consequences of interspecies floral visitation for both mutualistic partners. In the case of figs (Ficus), interspecific gene flow is expected to occur when their pollinating wasps (Agaonidae) visit more than one species. We studied reproductive isolating mechanisms in a clade of five dioecious fig species in sympatry. A new experimental method of manipulating pollinator introduction investigated the reproductive consequences of intra- and interspecific pollinator visitation for both mutualistic partners.
Results/Conclusions
Pollinators introduced into an alternative host pollinated and oviposited in receptive figs. Seed set was comparable between conspecific and heterospecific crosses and hybrids germinated, established and grew at rates comparable to non-hybrids. Fitness of pollinators, however, was compromised when ovipositing in a novel host. Although heterospecific pollinators induced gall formation, offspring did not develop to maturity in the new host. Microsatellite genotypes of the fig community indicated substantial but not absolute reproductive barriers among sympatric species. That only 1-2% of populations consist of hybrid individuals may be explained by strong selection against pollinator host switching in this system.