Synchrony of floral volatile emission with diurnal pollinators of possible decomposition mimic Asarum savatieri (Aristolochiaceae)

Abstract Background and Aims Floral scent is crucial for mediating plant-pollinator interactions, a primary driver of angiosperm diversity. The dynamic nature of olfactory cues means they can be fine-tuned to suit pollinator activity, making them an effective method of adaptation to local pollinator niches. Asarum sect. Heterotropa is one of the most species-rich lineages in Japan with remarkable variation in floral scents. We investigate how floral volatiles determine pollinator specificity in A. savatieri, a species with unusual floral phenology and scent, and examine how scent emission is synchronised with pollinator activity. Methods We identified pollinators by time-lapse photography and DNA barcoding, and recorded the visitation time of different animals. Pollinators were distinguished by the presence of pollen on their bodies. We examined floral scent composition and emission patterns by GC-MS and real time proton transfer reaction-mass spectrometry. We then assessed the degree of synchrony between volatile emission and visitation patterns of different floral visitors. Key results A. savatieri relies on dipterans for pollination, with Megaselia (Phoridae) being the most effective pollinator. Egg-laying by these flies inside the flowers suggests an oviposition-site mimicry system. Drosophila (Drosophilidae) were also frequent visitors, but their contribution to pollination remains unclear. The floral scent profile was dominated by volatiles resembling both carrion and rotting fruit, including dimethyl disulphide, alcohols, aldehydes and ketones, possibly suggesting a mixed mimicry system. These major volatiles followed a diurnal emission pattern with high emission synchronised exclusively to the daytime visitation by dipterans, including the pollinators. Conclusions The floral scent composition and oviposition by pollinating flies inside the flowers of A. savatieri indicates a deceptive pollination strategy of decomposition mimicry, possibly of a combination of carrion and rotting fruit. The synchrony between volatile emission and pollinators strongly suggests that these volatiles function as a fine-tuned adaptive trait to attract specific pollinators.