title: Lack of floral nectar reduces self-pollination in a fly-pollinated orchid.
abstract: One explanation for the widespread absence of floral nectar in many orchids is that it causes pollinators to visit fewer flowers on a plant, and thus reduces self-pollination. This, in turn, could increase fitness by reducing inbreeding depression in progeny and promoting pollen export. The few previous investigations of this hypothesis have all involved bee-pollinated orchids and some have given contradictory results. We studied the effects of adding artificial nectar (sucrose solution) to the spurs of a non-rewarding long-proboscid fly-pollinated orchid, Disa pulchra. Addition of nectar significantly increased the number of flowers probed by flies (2.6-fold), the time spent on a flower (5.4-fold), the number of pollinia removed per inflorescence (4.8-fold) and the proportion of removed pollen involved in self-pollination (3.5-fold). The level of self-pollination increased dramatically with the number of flowers probed by flies. Experimental self-pollination resulted in fruits with only half as many viable seeds as those arising from cross-pollination. Pollinators were more likely to fly long distances (>40 cm) when departing from non-rewarding inflorescences than when departing from rewarding ones. These findings provide support for the idea that floral deception serves to reduce pollinator-mediated self-pollination.
authors.affiliation: School of Biological and Conservation Sciences, University of KwaZulu Natal, Private Bag X01, Pietermaritzburg, ZA 3209, South Africa. jersa@centrum.cz
authors.forename: Jana
authors.initials: J
authors.lastname: Jersáková
authors.forename: Steven D
authors.initials: SD
authors.lastname: Johnson
mesh_terms: D000818:Animals; D004175:Diptera / Q000502:physiology*; D017753:Ecosystem; D005247:Feeding Behavior; D029595:Orchidaceae / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure; D011058:Pollen / Q000187:drug effects* / Q000502:physiology; D011156:Population Density; D012098:Reproduction; D013045:Species Specificity; D013395:Sucrose / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D013395:Sucrose