The importance of oligosulfides in the attraction of fly pollinators to the brood-site deceptive species Jaborosa rotacea (Solanaceae).

Abstract

Premise of research. Brood-site deceptive flowers use dishonest signals-especially floral odors that mimic oviposition substrates-to attract and deceive saprophilous insects to pollinate them. In this work, we recorded the pollinators of the sapromyiophilous species Jaborosa rotacea (Solanaceae) endemic to southern South America. Then, we characterized the floral volatiles of this species, and finally, we carried out field experiments to decouple the effects of scent and color as attractants for saprophilous flies. Methodology. We made direct observations of pollinators in a natural population of J. rotacea. We characterized floral volatiles by means of gas chromatography-mass spectrometry. Subsequently, we used a mixture of 2 oligosulfides (dimethyl disulfide and dimethyl trisulfide), which our analyses revealed were the main constituents of the floral scent of J. rotacea, as baits to determine the attractiveness of this olfactory signal to flies in a geographical region where J. rotacea is not present. Finally, we used the same foul-scented baits in arrays of artificial flowers resembling those of J. rotacea to assess the dual importance of olfactory and visual cues in fly attraction. Pivotal results. Pollination of J. rotacea occurs when saprophilous flies belonging to the families Calli-phoridae, Muscidae, and Sarcophagidae-with similar body dimensions to the anther-stigma distance in these flowers-acquire and deposit pollen in the flowers in a nototribic mode. Our chemical analyses revealed that J. rotacea floral scent is chemically simple and features 2 oligosulfide compounds (dimethyl disulfide and dimethyl trisulfide) commonly found in carrion-mimicking flowers. We found that saprophilous flies belonging to the same families that we recorded as pollinators ofJ. rotacea in its native South American habitat were attracted to foul-scented baits in temperate North America. The flies' visitation frequencies (recorded as approaches and landings on the artificial flowers) depended significantly on the presence of the foul-scented baits. Conclusions. These results support the hypothesis that oligosulfides are universally effective signals by which deceptive flowers may effect pollen dispersal by attracting flies that use carrion or carnivore feces as brood sites.