Plants use many mechanisms for their pollination. Now botanists have discovered a particularly sophisticated system among pipevines, based solely on deception.
The flowers of the Greek plant Aristolochia microstoma give off a foul musty odor that seems to mimic the smell of rotting insects. Pollinator flies of the genus Megaselia are likely attracted to this scent when they search for corpses of arthropods to mate and lay their eggs. Then, when they enter the tube of an Aristolochia flower, the flies are guided by hairs pointing downward into a small chamber that contains the female and male flower organs. Trapped inside, they deposit the pollen they carry on the stigma, before the stamens ripen and release pollen on the body of the flies. When the hairs blocking the entrance to the chamber wither, pollinators can escape and a new cycle can begin.
“Here we show that the flowers of A. microstomy emit a very unusual mixture of volatiles including alkylpyrazines, which are otherwise rarely produced by flowering plants. Our data suggest that this is the only plant species known to date to fool pollinators attracted to the scent of dead and decaying arthropods, rather than vertebrate carrion, ”explains the corresponding author, the Professor Stefan Dötterl, Head of the Plant Ecology Group and the Botanical Garden. at Paris-Lodron University in Salzburg, Austria.
Between 4 and 6% of flowering plants are deceptive: they use olfactory, colorful and / or tactile signals to announce a reward to pollinators, such as nectar, pollen or mating and breeding sites, but do not give not really this reward. Deception works because pollinators are unable to distinguish between reward and imitation. Deceptive pollination is typical of many orchids, but has also evolved independently several times in other plants, including the genus Aristolochia.
“Aristolochia contains more than 550 species distributed throughout the world, especially in the tropics and subtropics. Aristolochia species are mainly woody vines and herbaceous perennials with spectacular and complex flowers that temporarily trap their visitors for the purposes of pollination, ”explains study co-author Professor Christoph Neinhuis, who cultivates one of the largest collections of Aristoloches in the world at the Botanical Garden of the Technical University of Dresden.
“Many aristoloches are known to attract flies with floral scents, for example mimicking the smell of carrion or mammalian droppings, decaying plants or fungi,” explains Thomas Rupp, the study’s first author. “But our curiosity was piqued by A. microstomy, a small herb known only from Greece: unlike other Aristolochia with their colorful and showy flowers, A. microstomy has inconspicuous brownish flowers that lie horizontally – close to the ground or partially buried, among leaf litter or between rocks. “
“A. microstomy the flowers emit a simple but very unusual scent mixture that includes 2,5-dimethylpyrazine, a molecule that is not found in vertebrate carcasses or droppings, but in dead beetles. The unpleasant smell of carrion can be noticed by people even at a short distance, ”concludes botanist Prof. Stefan Wanke from TU Dresden.
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