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Archive - Dec 18, 2009

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Sexual Trickery by Orchids Promotes Efficient Pollination

New research has explained why orchids sometimes employ a seemingly limiting approach to attracting insect pollinators. While most flowering plants reward pollinators with tasty nectar, many orchid species turn to trickery. Some use what's called food deception. They produce flowers that look or smell as if they offer food, but actually offer no edible reward. Other orchids use sexual deception. They produce flowers that look or smell like female insects, usually bees or wasps. Males are drawn to the sexy flowers and attempt to mate with them. In doing so, they accidentally collect pollen on their bodies, which fertilizes the next orchid they visit. From an evolutionary perspective, the sexual strategy is a bit puzzling. Orchids that offer nectar or mimic food can attract a wide variety of food-seeking pollinators—bees, wasps, flies, ants, and so on. But sexual displays are only attractive to the males of a single species—a flower that looks like a female wasp is only going to attract male wasps, not other insects. So in appealing to sex, these orchids limit their potential pollinators, which would seem to be a reproductive disadvantage. The scientists, however, showed that populations of sexually deceptive orchids had higher "pollen transport efficiency" than the species with multiple pollinators. In other words, a higher percentage of the pollen that was taken from sexually deceptive orchids actually made it to another orchid of the same species. The orchids with multiple pollinators had more pollen taken from their flowers, but more of that pollen was lost—dropped to the ground or deposited in flowers of the wrong species. This research was published in the January 2010 issue of The American Naturalist.