Cheating is not always punished: killer female plants and pollination by deceit in the dwarf palm Chamaerops humilis.

Because the interests of mutualists are not perfectly aligned, conflicts between partners often arise, rendering mutualism unstable by allowing the evolution of cheating. The dwarf palm Chamaerops humilis is engaged in a nursery pollination mutualism with a specific weevil Derelomus chamaeropsis. In exchange for pollen dispersal, dwarf palms provide pollinators with food, shelter and egg-laying sites, but pollinators can develop only within male inflorescences. Here we show that weevils lay eggs in female inflorescences but processes associated with fruit development prevent larval development. The cost imposed by developing larvae probably differs between male and female plants, explaining why only females defend their inflorescences. Female palms thus cheat their pollinating weevil, and pollinators are expected to 'punish' (avoid) them. We found no evidence for such punishment: weevils visit female plants and the duration of visits to male and female inflorescences does not differ. Thus mutualists do not always co-operate and cheating may not be necessarily punished. Copyright 2004 Blackwell Publishing Ltd