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Mistletoe fruit-colour polymorphism and differential success in a habitat mosaic



Abstract  Polymorphisms in fruit colour are common in nature, but mechanistic explanations for the factor(s) responsible for their maintenance are for the most part lacking. Past studies have focused on frugivore colour preferences and fruit removal rates, but until recently there has been no evidence that these factors are responsible for the maintenance of the polymorphisms. For other types of genetic polymorphisms, habitat heterogeneity has been shown to play a role in their maintenance. Here we test the habitat heterogeneity hypothesis for a polymorphic New Zealand mistletoe. We show that red-fruited and orange-fruited morphs of the mistletoe Alepis flavida (Hook. F) Tiegh. (Loranthaceae) differ in their growth, mortality and flowering on forest edges and in forest interior. Red-fruited morphs, which are preferred by dispersers, grew, survived and flowered as well as orange-fruited morphs on edges, whereas orange-fruited morphs had much greater growth, survival, and flowering than red-fruited morphs in the forest interior. This is the first evidence that habitat-specific differences in growth and survival may contribute to maintaining fruit-colour polymorphisms.