Flower colours along an alpine altitude gradient, seen through the eyes of fly and bee pollinators

Abstract

Alpine flowers face multiple challenges in terms of abiotic and biotic factors, some of which may result in selection for certain colours at increasing altitude, in particular the changing pollinator species composition, which tends to move from bee-dominated at lower elevations to fly-dominated in high-alpine regions. To evaluate whether growing at altitude-and the associated change in the dominant pollinator groups present-has an effect on the colour of flowers, we analysed data collected from the Dovrefjell National Park in Norway. Unlike previous studies, however, we considered the flower colours according to ecologically relevant models of bee and fly colour vision and also their physical spectral properties independently of any colour vision system, rather than merely looking at human colour categories. The shift from bee to fly pollination with elevation might, according to the pollination syndrome hypothesis, lead to the prediction that flower colours should shift from more bee-blue and UVblue flowers (blue/violet to humans, i.e. colours traditionally associated with large bee pollinators) at low elevations to more bee-blue-green and green (yellow and white to humans-colours often linked to fly pollination) flowers at higher altitude. However, although there was a slight increase in bee-blue-green flowers and a decrease in beeblue flowers with increasing elevation, there were no statistically significant effects of altitude on flower colour as seen either by bees or by flies. Although flower colour is known to be constrained by evolutionary history, in this sample we also did not find evidence that phylogeny and elevation interact to determine flower colours in alpine areas.

The missing stink: sulphur compounds can mediate a shift between fly and wasp pollination systems

“…In such a situation, differences in effectiveness may depend on the abundance of the different pollinator types in particular regions or habitats. Both fly-pollinated Eucomis species are more common in high-altitude grasslands than are the wasppollinated species, possibly correlating with higher fly abundance and lower wasp abundance in this habitat (Arnold et al 2009). …”

“…The opponent system is based on the relative excitations of the two p-type and two y-type receptors, so the perceived colour depends on the receptor of each pair that is stimulated most strongly. Thus, the four possible colour categories (pþy þ , pþy2 , p2yþ and p2y2) correspond to the difference in excitation between the receptors of each type (Troje 1993;Arnold et al 2009). All stimuli within each category are considered indistinguishable to flies (Troje 1993).…”

The Importance of Oligosulfides in the Attraction of Fly Pollinators to the Brood-Site Deceptive SpeciesJaborosa rotacea(Solanaceae)

“…2D, 3A). To determine the similarity between J. rotacea and the artificial flowers, as perceived by carrion fly pollinators, we represented the reflectance spectra of natural and artificial flowers used in the bioassays as loci in the perceptual space of a blowfly color vision model (Troje 1993;Arnold et al 2009). According to this model, blowflies exhibit a categorical color vision system based on the relative excitations of the 2 pale-type and 2 yellow-type receptors.…”

“…Thus, color perception depends on the receptor of each pair that is stimulated most strongly, given 4 possible color categories (fly-UV, -blue, -yellow, and -purple). Stimuli with loci in the same color category would be indistinguishable to the fly (Troje 1993;Arnold et al 2009;Shuttleworth and Johnson 2010). To adjust for relative sensitivity of receptors to the background, we plotted color loci with reference to the leaf of J. rotacea (Chittka and Kevan 2005).…”

Floral colour versus phylogeny in structuring subalpine flowering communities

“…Whether coflowering species exhibit similar or divergent pollination syndromes has received little attention (but see Armbruster 2002). While a disproportionate number of species with a similar pollination syndrome may indicate the prevalence of a certain pollinator guild (Sargent & Vamosi 2008;Arnold et al 2009), it may also lead to pollinator competition (Caruso 2000;Botes et al 2008). Therefore, if pollinators do not exhibit fidelity to a particular species (i.e.…”