Pollination niche availability facilitates colonization of Guettarda speciosa with heteromorphic self-incompatibility on oceanic islands

Obligate out-breeding plants are considered relatively disadvantageous comparing with self-breeding plants when colonizing oceanic islets following long-distance dispersal owing to mate and pollinator limitation. The rarity of heterostyly, a typical out-breeding system, on oceanic islands seems a good proof. However, a heterostylous plant, Guettarda speciosa , is widely distributed on most tropical oceanic islets. Our research demonstrates that its heteromorphic self-incompatibility, plus herkogamy and long flower tube make it rely on pollinator for sexual reproduction, which is generally considered “disadvantageous” for island colonization. We hypothesize that available pollination niche will be a key factor for its colonization on islands. Our studies on remote coral islands show that G . speciosa has built equilibrium population with a 1:1 morph ratio. It could obtain pollination niche from the hawkmoth Agrius convolvuli . A pioneer island plant Ipomoea pes-caprae sustain the pollination niche by providing trophic resource for the larvae of the pollinator. Geographic pattern drawn by Ecological Niche Modelling further indicates the interaction between G . speciosa , A . convolvuli and I . pes-caprae can be bounded on those remote oceanic islands, explaining the colonization of G . speciosa distylous population. These findings demonstrated obligate out-breeding system could be maintained to acclimatize long distance dispersal, if the pollination niche is available.