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Facilitated selfing offers reproductive assurance: a mutualism between a hemipteran and carnivorous plant¹

²Botany Department, University of Cape Town, P Bag Rondebosch, South Africa 7701; ³Centre of Excellence in Natural Reserve Management, University of Western Australia, 444 Albany Highway, Albany WA 6330, Australia

Reproductive assurance is frequently used to explain the evolution of selfing but has become controversial from lack of evidence. We studied the pollination system of the near carnivorous plant genus Roridula and showed that reproductive assurance is important in this system. Hemipterans have a digestive mutualism with Roridula and have been implicated in pollination but flowers show adaptations to hymenopteran pollination. We deduce that hemipterans are the primary pollinators of Roridula because seed set is significantly reduced when hemipterans are excluded from the flowers. Using allozyme electrophoresis, we show that hemipterans are responsible for mostly selfed progeny. Although bees still pollinate Roridula on very rare occasions, their exclusion does not affect seed set. The complicated floral structures that occur in Roridula most likely evolved as adaptations for bee pollination. Resident hemipterans facilitate selfing by Roridula, and this acts as a reproductive assurance mechanism because it increases seed production and ensures that plants still reproduce in the absence of more motile, outcrossing pollinators.

Key Words: autogamy • facilitated selfing • mutualism • pollination • reproductive assurance • Roridula • seed set • self-fertilization