Pollinator and host sharing lead to hybridization and introgression in Panamanian free-standing figs, but not in their pollinator wasps

Obligate pollination mutualisms, in which plant and pollinator lineages
depend on each other for reproduction, often exhibit high levels of
species-specificity. However, cases in which two or more pollinator
species share a single host species (host sharing), or two or more host
species share a single pollinator species (pollinator sharing), are known
to occur in the current ecological time. Further, evidence for host
switching in evolutionary time is increasingly being recognized in these
systems. The degree to which departures from strict specificity
differentially affect the potential for hybridization and introgression in
the associated host or pollinator is unclear. We addressed this question
using genome-wide sequence data from five sympatric Panamanian
free-standing fig species (Ficus subgenus Pharmacosycea,
section Pharmacosycea) and their six associated fig pollinator
wasp species (Tetrapus). Two of the five fig species, F.
glabrata and F. maxima, were found to regularly share
pollinators. In these species, ongoing hybridization was demonstrated by
the detection of several first-generation (F1) hybrid individuals, and
historical introgression was indicated by phylogenetic network analysis.
In contrast, although two of the pollinator species regularly share hosts,
all six species were genetically distinct and deeply divergent, with no
evidence for either hybridization or introgression. This pattern is
consistent with results from other obligate pollination mutualisms,
suggesting that, in contrast to their host plants, pollinators appear to
be reproductively isolated, even when different species of pollinators
mate in shared hosts.