Pollinator sharing and hybridization in a pair of dioecious figs sheds light on the pathways to speciation

The dynamics and processes underlying the co-diversification of plant–pollinator interactions are of great interest to researchers of biodiversity and evolution. Co-speciation is generally considered to be a key process in generating the diversity of figs and their pollinating wasps. Groups of closely-related figs pollinated by separate wasps occur frequently and represent excellent opportunities to study ongoing diversification in this textbook mutualism. We study two closely-related sympatric dioecious figs (F. heterostyla and F. squamosa) in Xishuangbanna, southwest China, and aim to document what is likely to be the final stages of speciation between these species using a combination of trait data and experimental manipulation. Thirty-seven and 29 floral volatile compounds were identified from receptive F. heterostyla and F. squamosa figs respectively, with 25 compounds shared by both species. Interspecific variation in chemical dissimilarity was significant but relatively low. Ovipositor lengths lie well within the range required for access to heterospecific ovules, facilitating hybridization. Cross-introduction of wasps into figs was conducted and hybrid seeds were generated for all donor/recipient combinations. Wasps of F. heterostyla produce adult offspring in F. squamosa figs, while wasps of F. squamosa induce gall development in F. heterostyla figs and their offspring fail to mature in synchrony with their novel host. We record limited geographic barriers, limited volatile dissimilarity, compatible morphology, complementary reproductive phenologies and the production of hybrid seeds and wasp offspring. We hypothesize that this incomplete wasp specialization and incomplete reproductive isolation may generalize to other closely-related figs.

Methods
This data set was collated from manual counting. Methods for data acquiring, extracting, inclusion criteria, processing, and analysis are described in the paper's Material & Methods section.