Floral scent emission and pollinator attraction in two species of Gymnadenia (Orchidaceae)

Abstract

We investigated scent composition and pollinator attraction in two closely related orchids, Gymnadenia conopsea (L.) R.Br. s.l. and Gymnadenia odoratissima (L.) Rich. in four populations during the day and night. We collected pollinators of both species using hand nets and sampled floral odour by headspace sorption. We analysed the samples by gas chromatography with mass spectrometry to identify compounds and with electroantennographic detection to identify compounds with physiological activity in pollinators. In order to evaluate the attractiveness of the physiologically active compounds, we carried out trapping experiments in the field with single active odour substances and mixtures thereof. By collecting insects from flowers, we caught eight pollinators of G. conopsea, which were members of four Lepidoptera families, and 37 pollinators of G. odoratissima, from five Lepidopteran families. There was no overlap in pollinator species caught from the two orchids using nets. In the scent analyses, we identified 45 volatiles in G. conopsea of which three (benzyl acetate, eugenol, benzyl benzoate) were physiologically active. In G. odoratissima, 44 volatiles were identified, of which seven were physiologically active (benzaldehyde, phenylacetaldehyde, benzyl acetate, 1-phenyl-2,3-butandione, phenylethyl acetate, eugenol, and one unknown compound). In field bioassays using a mixture of the active G. odoratissima compounds and phenylacetaldehyde alone we caught a total of 25 moths, some of which carried Gymnadenia pollinia. A blend of the active G. conopsea volatiles placed in the G. odoratissima population did not attract any pollinators. The two orchids emitted different odour bouquets during the day and night, but G. odoratissima showed greater temporal differences in odour composition, with phenylacetaldehyde showing a significant increase during the night. The species differed considerably in floral odour emission and this differentiation was stronger in the active than non-active compounds. This differentiation of the two species, especially in the emission of active compounds, appears to have evolved under selection for attraction of different suites of Lepidopteran pollinators.

Mechanism of Spontaneous Autogamy in the Allogamous Lepidopteran Orchid Gymnadenia Conopsea (L.) R. Br. (Orchidaceae)

“…The results of this study reject the model that spontaneous autogamy is impossible in the lepidopteran orchid Gymnadenia conopsea (Gustafsson, 2000;Huber et al, 2005;Sletvold and Ågren, 2011). Although we based this on a very limited number of sampled plants, in each of the studied populations we noticed very low levels of autogamously set fruits (varying from 0.2% to 3.3% per analysed sample in a given population), which confirms the rare events of spontaneous autogamy in populations from England (Campbell, 1999) and Czech Republic (Jersáková and Kindlmann, 2004), and does not exclude the potential of higher rates of autogamy, which was recorded at 36% fruiting level after complete plant exclusion from pollinators in a population from Germany (Meyer et al, 2007).…”

“…Br., a species widely regarded as allogamous and which is currently the subject of intensive research (Jersáková et al, 2010;Stark et al 2011;Trávnícek et al, 2012;Meekers and Honnay, 2011;Sletvold and Ågren, 2011;Sletvold et al, 2012). The common view is that this plant is self-compatible but depends on pollinators (Gustafsson, 2000;Huber et al, 2005;Jersáková et al, 2010;Sletvold and Ågren, 2011;Sletvold et al, 2012) and that under pollinator deficiency, selfing is conducted via geitonogamy (Meekers and Honnay, 2011). Meanwhile, during research on the breeding system of orchids in Poland, fruits of G. conopsea were found after an experiment on spontaneous autogamy (I. Tałałaj, unpubl.…”

Evolution of ‘pollinator’- attracting signals in fungi

“…(e) Bioassays To test the electrophysiologically active compound for behavioural activity, attraction experiments with sticky traps were carried out at the Botanical Garden Zü rich (Huber et al 2005). The traps consisted of a white plastic disc 8 cm in diameter to which insect glue was applied (commercial insect exclusion adhesive; Temmen Insektenleim, Hattersheim) and covered with a plastic bowl.…”

Pollinator and Herbivore Attraction to Cucurbita Floral Volatiles

“…Plant volatiles can attract pollinators, provide learning cues for foraging insects, serve as herbivore repellants or attractants, or attract natural enemies of herbivores (De Moraes et al 1998;Pichersky and Gershenzon 2002;Cunningham et al 2004;Ashman et al 2005;Huber et al 2005). Despite the many ways that scent influences interactions between plants and insects, we know relatively little about how herbivores and pollinators respond to the same scent volatiles.…”