Abstract
Deceptive flowers decoy pollinators by advertising a reward, which finally is not provided. Numerous deceptive plants are pollinated by Diptera, but the attractive cues and deceptive strategies are only identified in a few cases. A typical fly-deceptive plant genus is Aristolochia, which evolved sophisticated trap flowers to temporarily capture pollinators. Though rarely demonstrated by experimental approaches, Aristolochia species are believed to chemically mimic brood sites, food sources for adult flies, or utilize sexual deception. Indeed, for most species, studies on scent composition and attractive signals are lacking. In this study, we focused on Aristolochia microstoma, a peculiar Greek endemic with flowers that are presented at ground level in the leaf litter or between rocks and are characterized by a unique morphology. We analyzed flower visitor and pollinator spectra and identified the floral scent composition using dynamic headspace and gas chromatography coupled to mass spectrometry (GC/MS). Female and male phorid flies (Phoridae) are the exclusive pollinators, although the flowers are also frequently visited by Sciaridae, as well as typical ground-dwelling arthropods, such as Collembola and arachnids. The carrion-like floral scent mainly consists of the oligosulphide dimethyldisulfide and the nitrogen-bearing compound 2,5-dimethylpyrazine. These compounds together are known to be released from decomposing insects, and thus, we conclude that pollinators are likely deceived by chemical imitation of invertebrate carrion, a deceptive strategy not described from another plant species so far.
Highlights
Deceptive pollination evolved in 4–6% of angiosperms (Renner, 2006), and relies on the inability of pollinators to distinguish between a true resource and the flower/inflorescence that imitates the reward (Brodmann et al, 2008, 2009; Urru et al, 2011)
Our findings show that A. microstoma is not pollinated by non-dipteran ground- or litter-dwelling arthropods, as Wanke (2006) hypothesized, but by flies, as all other Aristolochia species studied so far (Berjano et al, 2009)
The spatial position of A. microstoma flowers suggests that the pollinating Phoridae probably search for breeding sites or food close to the ground, in leaf litter, or between rocks
Summary
Deceptive pollination evolved in 4–6% of angiosperms (Renner, 2006), and relies on the inability of pollinators to distinguish between a true resource (e.g., mating partners, brood-sites, and food) and the flower/inflorescence that imitates the reward (Brodmann et al, 2008, 2009; Urru et al, 2011). Deceptive Pollination in Aristolochia microstoma traits (Vogel, 1978; Dafni, 1984; Stensmyr et al, 2002; Schiestl et al, 2003; Schiestl, 2005; Stökl et al, 2010; Woodcock et al, 2014). Fly-deceptive pollination strategies include mimicry of brood-sites (Stensmyr et al, 2002; Urru et al, 2011; Jürgens et al, 2013), food (e.g., Heiduk et al, 2016), and mating partners (Martel et al, 2016). In the early male phase the pollen is released, but trapping trichomes still block the exit, before they shrink and allow pollinators to leave the trap, loaded with pollen (Oelschlägel et al, 2009)
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