A Case Study with the Rocky Mountain Biological Laboratory

Image Credits: Galyna Andrushko

The laboratory or industrial floor are not the only places where the interaction of light in the world is measured; sometimes research takes you into the great outdoors. If you are lucky enough to be conducting your investigation in the open air, rugged and portable instruments are required. Researchers working at the Rocky Mountain Biological Laboratory (RMBL) in Gothic, Colorado near Crested Butte found the Avantes’ modular concept and portability were incredibly advantageous at an elevation of 2,889 meters.

The Pollinator/ Floral Characteristic Relationship

The relationship between pollinator and floral display could hold the key to revealing important answers in agriculture, conservation and ecology. A team led by Dr. Kenneth D. Whitney from RMBL studied this connection along altitude gradients at 67 sites around the West Elk Mountains, which surround the RMBL, across an altitude range of 1,300 meters.

Their aim was to quantify variations in community-weighted mean floral color across three essential components: hue, saturation, and brightness. They theorized an alteration in color values with the transition from bee-dominated to fly-dominated pollination at higher elevations.

Bug Vision

Bees utilize their color vision to detect flowers at a distance, that is well understood, and their large visual range extends further into the ultra-violet part of the spectrum. A bee’s vision is trichromatic, so they have three color receptors for ultraviolet, blue, and green. Bees which forage color discriminate and have strong wavelength-dependent preferences. Bee vision has been examined in great detail along with bee preference influence on flower evolution.

In contrast, flies possess only two kinds of photo receptors and therefore have restricted color vision and a shorter visual range. They are far less selective in flower choice, and seemingly have far less influence on flower evolution.

Biotic and Abiotic Evolutionary Mechanisms

Being able to pinpoint the drivers of evolutionary change is complex: biotic factors such as pollinator preference contend with abiotic factors like Average Daily UV dose and average temperature. To assess this, the researchers made a number of estimates about floral expression using the hypothesis that pollinator preferences would be one of the principal mechanisms.

Firstly, they predicted that as elevation rose (and bee pollinators became rarer), hue and saturation in the bee visual range would lessen. They also postulated that hues seen by flies and brightness in fly preferred wavelengths would increase.

Community Weighted Mean Color Data

To examine patterns of community-wide shifts in floral expression, the RMBL team formulated a method. This method used the percent of ground coverage of each recognized species in their study over each study area to calculate the weighted average of the raw spectra reflectance measurements to determine by the average reflectance of each species. This data was arbitrarily classified into eight spectral bands so-named for their presence in the human visual range UVB (300-315nm), UVA (315-400 nm), violet (400-440 nm), blue (440-500 nm), green (500-565 nm), yellow (565-590 nm), orange (590-625 nm), and red (625-700 nm).

Raw diffuse irradiance spectral data was obtained with the AvaSpec-ULS2048 spectrometer, which has the choice of a waterproof protective case (AvaTrek) for rugged portability and a wider variety of pioneering instruments, such as the new EVO electronics and CMOS detectors (US customers only).

Results & Analysis

A distinct elevation gradient in floral color expression in the visual ranges of the dominant pollinators in addition to visual-independent objective analysis were proven by the RMBL team. The shorter wavelengths favored by bees - corresponding to human UVB, UVA, and blue - decreased with elevation, whereas hues perceived by flies did not reveal the same connection. In the visual ranges of both pollinator species, saturation rises with elevation while brightness increases to a point, before decreasing again.

Their results provided evidence for expected shifts in floral hue expression in wavelengths favored by bees, giving weight to the premise that bee preference is a major evolutionary mechanism. Fly preferences do not have as strong an effect, as demonstrated by the lack of correlative elevation trends in fly hue ranges, nor do abiotic drivers have a greater effect at higher elevation.

Geographic Effects

The work of previous researchers was considered by the RMBL team before they formed their hypothesis, however, the effects of elevation may be inconsistent across all latitudes. Floral response at 3,000 m in the sub-alpine Rocky Mountains might be immensely different from floral expression at the same altitude in a more tropical setting.

Making sense of these associations between pollinators and floral display could be a very significant line of investigation as pollinators worldwide face ecological pressures on their populations.

The Avantes Commitment

Spectroscopy applications spread far beyond the normal boundaries of the lab. Anywhere light shines, spectroscopy is helping us comprehend the world around us.

As well as our line of portable spectrometers, Avantes has a range of sampling interface accessories which simplify field measurements.

References

*Gray, Michelle, et al. "Consistent shifts in pollinator‐relevant floral coloration along Rocky Mountain elevation gradients." Journal of Ecology (2018). *references Avantes equipment

De Ibarra, N. Hempel, Misha Vorobyev, and Randolf Menzel. "Mechanisms, functions and ecology of color vision in the honeybee." Journal of Comparative Physiology A 200.6 (2014): 411-433.

Dyer, Adrian G., Angelique C. Paulk, and David H. Reser. "Colour processing in complex environments: insights from the visual system of bees." Proceedings of the Royal Society of London B: Biological Sciences 278.1707 (2011): 952-959.

GOLDSMITH, TIMOTHY H., and HECTOR R. FERNANDEZ. "The sensitivity of housefly photoreceptors in the mid-ultraviolet and the limits of the visible spectrum." Journal of Experimental Biology 49.3 (1968): 669-677.

Riddle, Sharla. "How Bees See And Why It Matters." Bee Culture: The Magazine of American Beekeeping. (May 20, 2016).

This information has been sourced, reviewed and adapted from materials provided by Avantes BV.

For more information on this source, please visit Avantes BV.

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