Résumé
It is thought that speciation in phytophagous insects is often due to
colonization of novel host plants, because radiations of plant and insect
lineages are typically asynchronous. Recent phylogenetic comparisons have
supported this model of diversification for both insect herbivores and
specialized pollinators. An exceptional case where contemporaneous
plant–insect diversification might be expected is the obligate mutualism
between fig trees (Ficus species, Moraceae) and their pollinating wasps
(Agaonidae, Hymenoptera). The ubiquity and ecological significance of this
mutualism in tropical and subtropical ecosystems has long intrigued
biologists, but the systematic challenge posed by >750 interacting
species pairs has hindered progress toward understanding its evolutionary
history. In particular, taxon sampling and analytical tools have been
insufficient for large-scale cophylogenetic analyses. Here, we sampled
nearly 200 interacting pairs of fig and wasp species from across the
globe. Two supermatrices were assembled: on an average, wasps had
sequences from 77% of 6 genes (5.6 kb), figs had sequences from 60% of 5
genes (5.5 kb), and overall 850 new DNA sequences were generated for this
study. We also developed a new analytical tool, Jane 2, for event-based
phylogenetic reconciliation analysis of very large data sets. Separate
Bayesian phylogenetic analyses for figs and fig wasps under relaxed
molecular clock assumptions indicate Cretaceous diversification of crown
groups and contemporaneous divergence for nearly half of all fig and
pollinator lineages. Event-based cophylogenetic analyses further support
the codiversification hypothesis. Biogeographic analyses indicate that the
present-day distribution of fig and pollinator lineages is consistent with
a Eurasian origin and subsequent dispersal, rather than with Gondwanan
vicariance. Overall, our findings indicate that the fig-pollinator
mutualism represents an extreme case among plant–insect interactions of
coordinated dispersal and long-term codiversification.