No abstract
The dead horse arum, Helicodiceros muscivorus, is a conspicuous, foul smelling and thermogenic plant of the Araceae family. This Mediterranean arum lily copies several aspects of a carcass in order to attract carrion blowflies, which are subsequently exploited as unrewarded pollinators. We have previously shown that this plant exhibits a highly accurate olfactory carrion mimicry, which serves to attract the blowflies. In this study, we have investigated the role of thermogeny in the arum. We show that the thermogeny has a direct effect on the pollinators, altering their behaviour. By manipulating heat and odour release of the plant, we can show that the heat, produced along the appendix, is important to lure the flies to this structure, which is vital as the flies from the appendix are more prone to enter the trap chamber that houses the female and male florets. This study provides rare evidence for a direct functional role of thermogeny.
Flowers of the genus Arum are known to attract dung-breeding flies and beetles through olfactory deceit. In addition to this strategy, the genus has evolved several other pollination mechanisms. The present study aimed to characterize the pollination strategies of the Cretan Arum species by investigating the flowering phenology, thermogeny, inflorescence odours, and the pollinating fauna. The results obtained show that Arum cyrenaicum and Arum concinnatum emit a strong dung smell and exhibit the distinctive features associated with this pollination syndrome. Both species are highly thermogenic, have a similar odour profile and attract small-bodied Diptera. Although sharing the same habitat, these two plant species are never found growing sympatrically as a result of the early blooming period of A. cyrenaicum. By contrast, Arum creticum and Arum idaeum have evolved a more traditional and mutually beneficial pollination mechanism. The stinking smell has been replaced by a more flower-like odour that attracts bees (Lasioglossum sp.) and, occasionally, bugs (Dionconotus cruentatus). Although attracting the same pollinator, the main compound present in the odour of A. creticum is different from that of A. idaeum. Principal component analysis (PCA), based on physiologically active components of the flower odours determined by testing on the antenna of the Lasioglossum bee, revealed two different clusters, indicating that pollinators can potentially discriminate between the odours of the two species. A further PCA on the main floral odour volatiles as identified by gas chroatography-mass spectroscopy from all the Arum species under investigation displayed odour-based similarities and differences among the species. The PCA-gas chomotographyelectroantennographic detection active peaks analysis showed that the two species, A. creticum and A. idaeum, form two groups and are clearly separated from A. cyrenaicum and A. concinnatum, which, conversely, cluster together. The evolutionary forces and selective pressures leading to diversification of pollination mechanisms in the Cretan Arum spp. are discussed.
For centuries the wonderful looking, but foul smelling, Arum lilies have fascinated botanists. The floral odour of many species is believed to mimic faeces-the oviposition substrate of their pollinators, mainly coprophilous flies and beetles. But not all of the 29 Arum species produce a bad floral smell. The genus has evolved a variety of pollination mechanisms, including sweet and wine-like odours, and maybe even pheromone mimicry. In order to study the evolution of the pollination syndromes in Arum, a detailed and reliable phylogeny is a crucial basis. Here we present the first detailed molecular phylogeny of the genus Arum. By combining three chloroplast and one nuclear loci, as well as AFLPs, a highly resolved tree with good statistical support was obtained. The phylogeny is in most parts in congruence with the traditional classification of the genus. By comparing the phylogeny with the data on the pollination biology of the genus we could show that the mimicry of faeces is the oldest and most basal pollination mechanism, but is also present in the youngest and most derived species. The phylogeny presented here will help to study the evolution of deceptive pollination mechanisms in Arum.
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