Contrasting patterns of plant–pollinator interactions among four oil-secreting species of Iridaceae from Pampean and Cerrado provinces (Brazil)

Abstract

Flowers producing oil resources and oil bee pollinators are involved in one of the most specialized pollination strategies. Various species of Iridaceae tribe Tigridieae are characterized by floral oil-secreting structures called elaiophores, but specialized plant–pollinator interactions among these taxa remain poorly understood. This study focused on four South American species of Tigridieae in three genera to assess the nature and extent of ecological specialization related to oil flower/oil bee interactions. Proportion, frequency and behaviour of specialist and generalist pollinators were investigated, and experiments on plant breeding system and observations on floral biology were conducted. Species of Arhysoceble (specialist bees) and Halictidae (generalist bees) formed the most representative taxonomic groups of pollinators. Even though ecological specialization for oil bees was detected in Cypella amplimaculata and Cipura sp., contrasting patterns of specialization were observed not only among the different plant species studied but also between populations of Herbertia pulchella and Cipura formosa. Self-incompatibility was reported for H. pulchella and Cipura sp., whereas C. amplimaculata and C. formosa presented a mixed-breeding system. However, all species were pollinator dependent and patterns of ecological specialization were not dependent of plant breeding system. This study revealed also that interactions between oil bees and elaiophores are not reliable predictors for efficient pollination.