title: Pollination, mating and reproductive fitness in a plant population with bimodal floral-tube length.
abstract: Mating patterns and natural selection play important roles in determining whether genetic polymorphisms are maintained or lost. Here, we document an atypical population of Lapeirousia anceps (Iridaceae) with a bimodal distribution of floral-tube length and investigate the reproductive mechanisms associated with this pattern of variation. Flowers were visited exclusively by the long-proboscid fly Moegistorhynchus longirostris (Nemestrinidae), which exhibited a unimodal distribution of proboscis length and displayed a preference for long-tubed phenotypes. Despite being visited by a single pollinator species, allozyme markers revealed significant genetic differentiation between open-pollinated progeny of long- and short-tubed phenotypes suggesting mating barriers between them. We obtained direct evidence for mating barriers between the floral-tube phenotypes through observations of pollinator foraging, controlled hand pollinations and measurements of pollen competition and seed set. Intermediate tube-length phenotypes produced fewer seeds in the field than either long- or short-tubed phenotypes. Although floral-tube length bimodality may not be a stable state over long timescales, reproductive barriers to mating and low 'hybrid' fitness have the potential to contribute to the maintenance of this state in the short term.
authors.affiliation: Department of Botany and Zoology, Stellenbosch University, Stellenbosch, South Africa.
authors.forename: B
authors.initials: B
authors.lastname: Anderson
authors.affiliation: Department of Botany and Zoology, Stellenbosch University, Stellenbosch, South Africa.
authors.forename: A
authors.initials: A
authors.lastname: Pauw
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada.
authors.forename: W W
authors.initials: WW
authors.lastname: Cole
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada.
authors.forename: S C H
authors.initials: SC
authors.lastname: Barrett
mesh_terms: D000818:Animals; D035264:Flowers; D056084:Genetic Fitness; D027621:Iridaceae / Q000254:growth & development / Q000502:physiology*; D054817:Pollination; D012098:Reproduction; D012641:Selection, Genetic
keywords: disruptive selection; floral polymorphism; genetic incompatibilities; long-proboscid fly; mating; pollination; pollinator preference; reproductive barriers; trait bimodality