Separating selection by diurnal and nocturnal pollinators on floral display and spur length in Gymnadenia conopsea

Abstract

Most plants attract multiple flower visitors that may vary widely in their effectiveness as pollinators. Floral evolution is expected to reflect interactions with the most important pollinators, but few studies have quantified the contribution of different pollinators to current selection on floral traits. To compare selection mediated by diurnal and nocturnal pollinators on floral display and spur length in the rewarding orchid Gymnadenia conopsea, we manipulated the environment by conducting supplemental hand-pollinations and selective pollinator exclusions in two populations in central Norway. In both populations, the exclusion of diurnal pollinators significantly reduced seed production compared to open pollination, whereas the exclusion of nocturnal pollinators did not. There was significant selection on traits expected to influence pollinator attraction and pollination efficiency in both the diurnal and nocturnal pollination treatment. The relative strength of selection among plants exposed to diurnal and nocturnal visitors varied among traits and populations, but the direction of selection was consistent. The results suggest that diurnal pollinators are more important than nocturnal pollinators for seed production in the study populations, but that both categories contribute to selection on floral morphology. The study illustrates how experimental manipulations can link specific categories of pollinators to observed selection on floral traits, and thus improve our understanding of how species interactions shape patterns of selection.

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

“…is a perennial species occurring on calcareous soils in grazed meadows and in the margins of marshes and fens, both in well-lit open habitats and in significantly shaded sites (Vakhrameeva et al, 2008;Sletvold et al, 2012). The species is distributed over all of Europe and a considerable part of Asia (Hultén and Fries, 1986).…”

“…During both day and night, flowers emit a weak vanilla-like but slightly unpleasant scent (Marhold et al, 2005), which is produced in osmophores on the surface of the labellum and lateral sepals (Stpiczyńska, 2001). Sletvold et al (2012) present this species as an orchid with a semi-generalised pollination system because it receives visits from a large number of species, though most of them are lepidopteran (listed in Claessens and Kleynen, 2011). In other populations, distinct differences in pollination efficiency between butterflies and moths have been observed (Vöth, 2000;Meyer et al, 2007;Sletvold et al, 2012), as this species may represent an intermediate stage in the adaptation to diurnal versus nocturnal pollinators (Claessens and Kleynen, 2011).…”

“…Sletvold et al (2012) present this species as an orchid with a semi-generalised pollination system because it receives visits from a large number of species, though most of them are lepidopteran (listed in Claessens and Kleynen, 2011). In other populations, distinct differences in pollination efficiency between butterflies and moths have been observed (Vöth, 2000;Meyer et al, 2007;Sletvold et al, 2012), as this species may represent an intermediate stage in the adaptation to diurnal versus nocturnal pollinators (Claessens and Kleynen, 2011). The fruiting level varies significantly between different sites and ranges from 23% to 95.5% (compiled in Claessens and Kleynen, 2011).…”

“…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.…”

Vegetation context influences the strength and targets of pollinator‐mediated selection in a deceptive orchid

“…Pollinators have been experimentally identified as agents of selection both on traits likely to be involved in pollinator attraction and on traits affecting pollination efficiency, but the proportion of selection that can be attributed to pollinators varies among traits (Sletvold et al 2010a(Sletvold et al , 2012. There may also be considerable spatiotemporal variation in the strength of pollinator-mediated selection on a given trait (Sletvold and Å gren 2010), suggesting that manipulations of both the pollination environment and other putative selective factors are required to understand variation in selection on floral traits.…”