Food Reward Chemistry Explains a Novel Pollinator Shift and Vestigialization of Long Floral Spurs in an Orchid

•Satyrium longicauda is characterized by two pollination ecotypes•Pollination oil-collecting bees derived from moth pollination•The pollinator shift process associated with pre-adaptation and vestigialization•Minor modifications in floral chemistry can initiate major shifts During the evolutionary history of flowering plants, transitions between groups (pollinator shifts) have been frequent,1van der Niet T. Johnson S.D. Phylogenetic evidence for pollinator-driven diversification angiosperms.Trends Ecol. Evol. 2012; 27: 353-361Abstract Full Text PDF PubMed Scopus (225) Google Scholar contributed to spectacular radiation angiosperms.2Hernández-Hernández Wiens J.J. Why are there so many plants? A multiscale analysis plant diversification.Am. Nat. 2020; 195: 948-963Crossref (22) Although evolution traits during has studied real time under controlled laboratory conditions,3Gervasi D.D.L. Schiestl F.P. Real-time divergent plants driven pollinators.Nat. 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Remarkably, flowers bee-pollinated form similar morphology, color, overall volatile those moth-pollinated forms, but differ having spurs that mostly devoid nectar, an elevated presence oil-derived compound diacetin, which use as cue oil presence.8Schaffler I. Steiner K.E. Haid M. Berkel S.S. Gerlach G. Wessjohann L. Dotterl S. Diacetin, reliable private communication channel specialized system.Sci. Rep. 2015; 5: 11Crossref (44) Experiments demonstrated long critical form, not needed form. We conclude was mediated switch reward. ancestral diacetin might served pollination, whereas current mismatch flower morphology due retention vestigial spurs. These results elucidate sequence early stages help explain assembly suites co-varying through vestigialization.9Armbruster Pélabon C. Hansen T.F. Bolstad G.H. Macroevolutionary patterns accuracy: comparison three genera.New Phytol. 183: 600-617Crossref (41) 10Steiner K. beetle South orchid.Am. J. 1998; 85: 1180-1193Crossref (61) 11Fong D.W. Kane T.C. Culver D.C. Vestigialization loss nonfunctional characters.Annu. 1995; 26: 249-268Crossref (155) 12Lahti N.A. Ajie B.C. Otto S.P. Hendry A.P. Blumstein D.T. Coss R.G. Donohue Foster S.A. Relaxed selection wild.Trends 24: 487-496Abstract (337) Pollinator occur when populations same adapt different pollinators.13Stebbins G.L. Adaptive reproductive characteristics angiosperms. Pollination mechanisms.Annu. 1970; 1: 307-326Crossref This formation ecotypes.5van Scholar,14Grant V. Grant K.A. Flower Phlox family. Columbia University Press, New York1965Google 15Armbruster Patterns character divergence ecotypes Dalechampia scandens (Euphorbiaceae).Evolution. 1985; 39: 733-752Crossref (99) 16Johnson plants.in: Harder L.D. Barrett S.C.H. ecology flowers. Oxford Oxford2006: 295-310Google Such intraspecific variation represent ideal model systems investigate underlying shifts. discovered longicauda, highly variable southern grassland its center diversity global hotspot biodiversity.17Hall A.V. revision Satyrium.Contr. Bolus Herb. 1982; 10: 1-142Google Only subspecific taxa currently recognized,17Hall extensive fieldwork frequent co-occurrence multiple discrete forms (see below). Studying sympatry offers great advantages over studying allopatric populations: sympatric (1) minimizes environmental causes phenotypic differences reveals their genetic basis18Turesson genotypical response habitat.Hereditas. 1922; 3: 211-350Crossref (448) (2) excludes possibility observed interactions reflect geographical turnover assemblages19Armbruster Floral angiosperm divergence, fitness trade-offs realized accuracy.AoB Plants. 6: 24Crossref (78) Scholar,20Eckert C.G. Effect fauna mating system Decodon verticillatus (Lythraceae).Int. 2002; 163: 123-132Crossref (39) rather than function traits. Within circa 1 km2 site, identified six including spur length be unambiguously diagnosed number position leaves habitat (Figure S1; Table S1). Fruit set absent visitors were excluded all 70%–100% cross-pollinated fruit, indicating dependence confirming previous done one forms.21Johnson Harris L.F. Proches breeding selected wildflowers community.S. Afr. 75: 630-645Crossref (21) Previous work shown most common pollinated nocturnal moths.22Johnson Peter C.I. Ellis A.G. Boberg E. Botes Diverse twin-spurred genus grasslands.Plant 2011; 292: 95-103Crossref (16) conform syndrome moth-pollination, white, sweetly scented relatively spurs.23van Liltved W.R. More meets eye: morphological phylogenetic long-spurred, white-flowered (Orchidaceae) Africa.Bot. Linn. Soc. 166: 417-430Crossref (9) Scholar,24Vogel Blütenbiologische Typen als Elemente Sippengliederug, dargestellt anhand Flora Südafrikas. Fischer, Jena1954Google Our initial hypothesis moths, could moths tongue lengths.25Johnson Moré Amorim F.W. Haber W.A. Frankie G.W. Stanley D.A. Coccuci A.A. Raguso R.A. short it: hawkmoth niches interaction networks.Funct. 31: 101-115Crossref To identify pollinators, made direct observations used motion-activated cameras close-up lenses.26Johnson Balducci M.G. Bijl A. Castañeda-Zárate Cozien R.J. Ortmann C.R. Van From dusk till dawn: camera traps reveal diel feeding hawkmoths.Ecol. Entomol. 45: 751-755Crossref (5) Five out (MOTH1–MOTH5), visited exclusively predominantly hawkmoths (Sphingidae) settling (Noctuidae), carried pollinaria 1; S2; Video For these (MOTH1 MOTH3), occasional visits diurnal long-tongued nemestrinid flies also recorded (Table S2). Contrary our expectations, (BEE) did receive any frequently (n = 134) Rediviva neliana bees, 63.4% All 15 individuals captured while visiting female, significant sex bias (exact binomial test: p < 0.001). behavior mechanism differed markedly MOTH BEE forms: inserted proboscides into hovering front of, on, inflorescences, attached proboscis In contrast, insert forelegs probe galeate labellum. Pollinaria (mean ± SD: 4.0 2.70, range 1–12) tibia bees’ S1) (cf. Pauw27Pauw syndromes accurately predict (Rediviva peringueyi, Melittidae) guild orchids (Coryciinae).Am. 2006; 93: 917-926Crossref (137) Scholar). site placement, angle orientation other area.28Waterman Bidartondo M.I. Stofberg Combs J.K. Gebauer Savolainen Barraclough T.G. Pauw effects above- belowground mutualisms coexistence.Am. 177: E54-E68Crossref (145) https://www.cell.com/cms/asset/02609e8a-2141-45dd-ab3e-07e3255b5add/mmc3.mp4Loading ... Download .mp4 (3.4 MB) Help files S1. Clips Moths Oil-Collecting Bees Related Figure confirm periodicity (in manner independent observer- trigger-bias influence trapping, respectively), systematically compared pollinarium removal intervals.29van Jürgens Is timing scent emission correlated insect visitor activity species?.Plant Biol (Stuttg). 17: 226-237Crossref (13) Results showed five significantly higher at night day, 1). Natural fruit among 6 ranged 79%–90%, contribute fecundity. prediction based traits, combined suggest existence ecotype closely resembles (MOTH) raising questions about mediate partitioning pollinators co-occurring ecotypes. consistent nectar foraging. involved insertion legs flowers, suggestive foraging mode (Video Female visit only collect oil, they densely pilose forelegs.30Vogel Diascia - oil-based symbiosis Africa.Acta Neerl. 1984; 33: 509-518Crossref 31Manning J.C. Brothers D.J. relations four Natal.J. South. 1986; 49: 107-114Google 32Whitehead V.B. 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Lond. 129: 213-226Google glycerol thought derivative biosynthesis considered universal neliana, form.8Schaffler Consistent staining, GCMS analyses confirmed triacetin 2). quantities much (diacetin: ?2 113.52, 0.001, bee:moth production ratio 7.83; triacetin: 25.731, 11.46) antennal responses concentration8Schaffler why Analyses unique 2-tridecanone 2), known trigger bees.8Schaffler Presence unknown species,29van reported other—distantly related—Satyrium bees.37Steiner Kaiser Strong oil-secreting Africa.Am. 98: 1663-1679Crossref Scholar,38Whitehead Oil-collecting winter rainfall area Africa (Melittidae, Rediviva).Ann. Mus. 2001; 108: 143-277Google characterize attraction fit pollinator, quantified headspace volatiles across forms. Analysis spectral reflectance vision strong overlap several multivariate 12 quantitative morphometric although cluster (PERMANOVA: f 127.36, 0.001), no clear discontinuities Furthermore, mean Euclidean distance (?2 0.334, 0.56). sampled day factors (2-way PERMANOVA: 45.646, 0.001; 13.556, × 6.0347, 0.001) characters, Bray-Curtis similarity comparisons both (day: 0.095, 0.76; night: 2.64, 0.10) 2; S3). percentage dominated aromatic particular (E)-cinnamyl alcohol, compounds dominate Several elicit B. schenki.36Johnson Given shape, scent, predicted lack visitation suitable Measurements volume sugar concentration almost complete absence 0.5–2.5 ?l, resulting total availability 0.2–0.8 mg near-absence apparent collection galea longer Some oil-producing spurs,39Hollens Kuhlmann spur-ious inference: more spurless Diascia-Rediviva mutualisms.Flora. 232: 73-82Crossref usually matches foreleg pollinating bees.40Steiner Whitehead adaptation Redivivia Diascia.Evolution. 1990; 44: 1701-1707Crossref Scholar,41Pauw Kahnt Michez D. 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