Pollinator sharing, copollination, and speciation by host shifting among six closely related dioecious fig species

The obligate pollination mutualism between figs (Ficus, Moraceae) and
pollinator wasps (Agaonidae, Hymenoptera) is a classic example of
cospeciation. However, examples of phylogenetic incongruencies between
figs and their pollinators suggest that pollinators may speciate by host
shifting. To investigate the mechanism of speciation by host shifting, we
examined the phylogenetic relationships and population genetic structures
of six closely related fig species and their pollinators from southern
China and Taiwan-Ryukyu islands using various molecular markers. The
results revealed 1) an extraordinary case of pollinator sharing, in which
five distinct fig species share a single pollinator species in southern
China; 2) two types of copollination, namely, sympatric copollination by
pollinator duplication or pollinator migration, and allopatric
copollination by host migration and new pollinator acquisition; 3) fig
species from southern China have colonized Taiwan repeatedly and one of
these events has been followed by host shifting, host specificity
reestablishment, and pollinator speciation, in order. Based on our
results, we propose a model for pollinator speciation by host shifting in
which reestablishment of host-specificity plays a central role in the
speciation process. These findings provide important insights into
understanding the mechanisms underlying pollinator speciation and host
specificity in obligate pollination mutualism.