Fig. 6: Establishment of the mutualistic relationships in the F. erecta complex and its pollinators (in parentheses) in the Taiwan-Ryukyu islands (a–d) and a model for host-shift speciation proposed in this study (e).

a The divergence of F. vaccinioides–B. yeni/B. sp. and F. formosana–B. silvestriana. b F. erecta migrated into Taiwan from mainland China. Blastophaga sp. host-shifted to F. erecta and speciated into B. nipponica. Then, the distribution range of F. erecta–B. nipponica expanded northward to the Ryukyu Islands and Japan. The chronology in a and b is based on the dating analysis of the pollinators (Supplementary Fig. 10). c F. formosana probably migrated into Taiwan recently from mainland China, and B. nipponica host-shifted to F. formosana; at present, F. erecta and F. formosana appear to share B. nipponica including “B. taiwanensis” in Taiwan. d B. nipponica dispersed from Taiwan to the Fujian region (FJ) of mainland China, resulting in an example of sympatric co-pollination. e The proposed model for the host-shift speciation events described in this study consists of four stages: (1) Host figs migrate into a new niche without their original pollinators; (2) The migrated host figs are pollinated by new wasps (host shifting); as a result, two host fig species share one wasp pollinator (pollinator sharing); (3) The host-shifted wasps evolve and become associated with the host figs that migrated (host-specificity reestablishment), and reproductive isolation occurs; (4) Genetic divergence proceeds and speciation occurs. These images show only the evolutionary events, not the details of the evolution of figs and pollinators during these processes.