The evolution of tachinid pollination in Neotinea ustulata is related to floral cuticular composition and the combined high relative production of (Z)‐11‐C23/C25enes

Abstract

Among terrestrial orchids, and particularly among the subtribe Orchidinae, flies are underrepresented as pollinators. The European Neotinea ustulata, which developed specialized pollination by tachinid flies, is known to produce high relative concentrations of the floral cuticular alkenes (Z)-11-tricosene and (Z)-11-pentacosene (referred to as (Z)-11-C23/C25enes), which seem to be uncommon among orchid flowers. If the evolution of tachinid pollination is related to that of (Z)-11-C23/C25enes, we can expect that closely related species have a different floral chemical pattern and significantly small or no production of (Z)-11-C23/C25enes, independently of their pollinator guild identity (e.g., bees, flies, moths). We chemically compared the floral cuticular composition among Neotinea species, performed electrophysiological analyses, reconstructed the phylogenetic Orchidinae tree, and identified the evolutionary history of pollinator guild and (Z)-11-C23/C25enes production within the Orchidinae. Neotinea ustulata has evolved a markedly different floral cuticular composition compared to other Neotinea and produces both compounds ((Z)-11-C23/C25enes) in high relative quantities (i.e., above 8% in combination), which are detectable by tachinid antennae. Moreover, most Orchidinae taxa have minimal or no production of these alkenes, independently of the identity of their pollinator guild. Our ancestral reconstruction suggested that (Z)-11-C23/C25enes production was an evolutionary exaptation in Neotinea, whereas tachinid pollination was a unique evolutionary innovation for N. ustulata. Floral cuticular composition and, in particular, the combined production of (Z)-11-C23/C25enes at relatively high concentrations is intimately linked to the evolution of tachinid pollination within the Orchidinae.

The volatile chemistry of orchid pollination

“…46 Alkenes have also been detected, but not yet shown to be biologically active, in a range of other non-sexually deceptive orchids (e.g. Maxillaria, Anacamptis, Gymnadenia, Serapias, Dactylorhiza, Himantoglossum, Platanthera, Neotinea [47][48][49] ) suggesting alkene production in orchids is not unusual.…”

“…Similarly, studies utilising both headspace and solvent extractions oen nd limited overlap between the results of each method. 47,172 On the other hand, SPME has been unsuccessful for isolation of bioactive compounds from Australian Drakaea owers despite multiple attempts (B. Bohman, pers. comm.…”

“…183,184 These developments have facilitated comparative studies of comprehensive oral volatilomes, which complement structural elucidation of new specic semiochemicals to enable new insights into the roles of chemical communication. Such "chemical phenotyping" studies have, for example, revealed relationships between chemical composition and the phylogeny in taxa of perfume rewarding orchids, 59,125,135 disentangled visual and olfactory signals in mushroom-mimicking Dracula orchids, 51 showed correlations between oral cuticular hydrocarbon compositions and y pollinators in Neotinea, 47 and distinguished chemotypes of sexually deceptive Drakaea orchids. 170 Here, it is important to note that to identify any specic compounds revealed by such analyses as potentially biologically relevant, comparison of retention data and mass spectral fragmentations with those of fully characterised reference compounds is critical.…”

“…Examples of this approach have already been successfully applied in perfume rewarding and sexually deceptive pollination systems. 47,59,135,170 Chemical phenotyping may also provide important clues about the evolution of pollination strategy shis and the evolution of novel semiochemicals. Thus, we recommend this approach as a potentially fruitful area for further research.…”

Chemical communication between plants and insects

“…In this special issue of the Journal of Systematics and Evolution , we present a collection of 10 papers addressing these challenges through original research and comprehensive reviews of relevant subfields. The contributions can be organized into four primary themes: (i) community‐level communication theory (Zu et al, 2022) and its application to plant–pollinator communities (Yang et al, 2022); (ii) the evolutionary history of communication from a phylogenetic and macroevolutionary perspective (Martel et al, 2021; Schwery et al, 2022); (iii) various communication types, including plant–pollinator (Martel et al, 2021), plant–pest (Fang et al, 2023), and plant–fungi–insect interactions (Xu et al, 2023); and (iv) an exploration of different communication factors such as distyly (Zeng et al, 2022), odor dynamics (Feng et al, 2022), chemical structures (Zhang et al, 2022), and the impact of herbicides (Ramos et al, 2022).…”