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Floral scent and deceptive pollination in Aristolochia

Subject Area Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems
Sensory and Behavioural Biology
Ecology and Biodiversity of Plants and Ecosystems
Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
Term from 2018 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 395142116
 
Final Report Year 2023

Final Report Abstract

Interactions between plants and other organisms represent one of the most fascinating topics in ecology and evolutionary biology, among which pollination of angiosperms by animals consistently evokes particular scientific interest. During the last decades many studies considerably contributed to our mechanistic understanding of the diversity in plant-pollinator interactions. However, our knowledge about the specific nature of many pollination systems, especially those between deceptive plants and their dipteran pollinators, is still limited. West Mediterranean Aristolochia species are known to be pollinated by flies, with the resource imitated / mimicked unknown for most of the species. The overall goals of the project were to analyse the pollinator fauna of six selected Mediterranean Aristolochia species, to study the chemical ecology of pollinator attraction and the deceptive strategies of the plants, and to analyse the Diptera fauna available in the habitats. All studied species were visited by a high taxonomic diversity of (mainly dipteran) visitors, but the visitor assemblages were vastly dominated by only one or two fly families each. We found that A. microstoma and A. pallida were mainly pollinated by female Phoride, whereas A. lutea and A. paucinervis by male Phoridae (Megaselia spp.). Female Phoridae were also the main pollinators in A. clusii, followed by Sphaeroceridae, Chloropidae and Ceratopogonidae. In contrast to the five species mentioned above, phorids played a minor role as pollinator in A. baetica, which was predominantly pollinated by male and female drosophilids (especially several species of Drosophila). Our chemo-ecological analyses revealed that A. microstoma and A. pallida release carrion-like scents, vastly dominated by 2,5-dimethylpyrazine, dimethyl disulfide and dimethyl trisulfide, and imitate the scent of insect carrion to deceive their phorid pollinators, representing a novel sapromyiophilous pollination strategy among deceptive plants. Aristolochia lutea and A. paucinervis are both basically scentless to the human nose. Still, our chemical analyses revealed various compounds, mainly aliphatic alcohols and ketones, among them rare or even novel floral scents: 4-methyl-2-pentanol, (E)-3-methyl-3-penten-2-ol, (E)-3-methyl-3-penten-2-one, 5-methyl-3-hexanone. We found most of these compounds also in female, but not in male Phoridae, suggesting that A. lutea and A. paucinervis imitate female sex pheromones of their male Phoridae pollinators. If indeed true, the finding would be exceptional, given that pollination by sexual deception is almost exclusively restricted to orchids. Finally, we found that A. baetica emits volatiles typically produced by yeast fermenting fruits, such as acetoin, acetoin acetate, 2,3-butanediol and mono- and diacetates thereof, and 2-phenylethanol to chemically imitate such substrate and attract / deceive their drosophilid pollinators. A comparison of the locally available fly communities with the flower visitors trapped by the plants shows that the plants highly specifically attract a subset of flies present at the respective habitats.

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