Cospeciation of figs and fig‐wasps: a case study of endemic species pairs in the Ogasawara Islands

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AbstractThe interactions between figs (Ficus, Moraceae) and fig‐wasps (Agaonidae, Chalcidoidea, Hymenoptera) are special plant‐pollinator relationships that are highly species‐specific, in that each fig species is pollinated by a single fig‐wasp species that can breed only in that particular fig species. This study examined the degree of pre‐mating isolation and genetic differentiation for three fig/fig‐wasp pairs endemic to the Ogasawara Islands. Simple Y‐tube tests revealed that fig‐wasps fromFicus nishimuraeand “Higashidaira type” chose their own host figs significantly more often, while fig‐wasps fromF. boninsimaedid not. Based on RAPD markers, the genetic differentiation among the fig species was low, butF. boninsimaeformed a cluster within theF. nishimuraecluster. The Higashidaira type has been derived from a subpopulation ofF. nishimurae. Five mitochondrial DNA haplotypes were found in the fig‐wasps and each haplotype correlated well with the fig species on their island of origin. These results led to a three‐step hypothesis on the cospeciation process: (1) spatial separation of fig/fig‐wasp populations arises; (2) gene flow is restricted and character differentiation of fig‐wasps occurs; (3) there is further restriction of gene flow and genetic and character differentiation of figs.