On the Trails: Considering variation in flower colors

There’s way more than blue genes.

Wild iris (Iris setosa) comes in a variety of shades, from the usual purple to pale lavender or reddish. (Courtesy Photo / Denise Carroll)

Wild iris (Iris setosa) comes in a variety of shades, from the usual purple to pale lavender or reddish. (Courtesy Photo / Denise Carroll)

The flowers of any species are typically controlled by genes and are usually of a certain color: bog cranberry typically has pink flowers, starflowers are white, forget-me-nots are blue, and so on. Biologists often think that deviations from those norms would break up the important relationships with the usual pollinators of each species, causing failures of reproduction. And perhaps that often happens. However, over the course of thousands of years of evolution, there must have been many mutations of flower color (including ultraviolet) and many of them must have found an adequate pollinator — otherwise we would not see the array of flower colors that we do. Natural selection favored some of those mutants, and they persisted, then becoming more common (and eventually the norm) in a population.

Wild iris (Iris setosa) comes in a variety of shades, from the usual purple to pale lavender or reddish. (Courtesy Photo / Deana Barajas)

Wild iris (Iris setosa) comes in a variety of shades, from the usual purple to pale lavender or reddish. (Courtesy Photo / Deana Barajas)

So it may be interesting to consider flower-color variation in some of our local species. In some species, flower color is almost constant across the population: e.g. lupines are blue, with occasional pink- or white-flowered individuals; northern geraniums are pink, with rare white-flowered individuals. In other cases, there’s a continuous range of hue: wild iris flowers are usually deep, rich purple, but some are paler, even lavender, while others are various shades of reddish purple. Rice-root (chocolate lily to local folks) flowers are usually maroon-brown, but some plants make flowers that are mostly yellow with brown lines, and there are many intermediates. On the road above Eaglecrest, there’s a stand of white-flowered river-beauty, not just one individual but an aggregation of them, quite unlike the usual pink-flowered ones.

That raises obvious questions about the pollination of these variants. Are the variations determined simply by genes or are there environmental effects too? Who pollinates the variants? Do pollinators favor the normal deep purple irises, or the brown rice-roots, thus reinforcing the norms? How well do the variants reproduce: Do pink or white lupines reproduce (as either pollen donors or pollen receivers) as well as blue ones; do yellow rice-roots do as well as brown ones? If so, could the variant colors spread? Could the white-flowered river beauties show how a variant could spread more widely?

There are cases of environmental effects on flower color, with potential consequences for pollinator interactions. The hues themselves are presumably determined genetically, but the environment affects gene expression — which genes are turned on or off, for instance. The best known, perhaps, is that in certain species of hydrangea the colorful sepals can be blue, or red, or something in between. Flower color in this hydrangea is sensitive to soil conditions: in acid soils that contain aluminum ions, the flowers are blue, but if the soil is alkaline or neutral, the flowers are pink or red. The color change may affect visitations by pollinators, but so far I have found no information about this.

Wild iris (Iris setosa) comes in a variety of shades, from the usual purple to pale lavender or reddish. (Courtesy Photo / Denise Carroll)

Wild iris (Iris setosa) comes in a variety of shades, from the usual purple to pale lavender or reddish. (Courtesy Photo / Denise Carroll)

However, in two other, less well-known, instances, flower-color changes on individual plants are associated with pollinator changes:

Moricandia arvensis is a type of mustard that grows in semiarid and arid ecosystems in the western Mediterranean area. Recent studies have found that the difference between spring climate conditions (mild, wet) and summer conditions (hot, dry) produce quite dramatic changes in the flowers produced by each individual plant. In one set of conditions, the flowers have large, purple petals that reflect UV light; in the other set of conditions, the petals are small, white, and UV-absorbing, with a different shape as well. Experiments showed that the floral changes are a response to changes in temperature and photoperiod that correspond to the seasonal shift. Conveniently, there were corresponding changes in the pollinators of the flowers (from long-tongued bees to small bees, small beetles, and butterflies) and seed production was achieved.

Equally intriguing is a recent study that found effects of herbivory on floral traits. Black mustard (Brassica nigra) is native to parts of the Old World and considered to be invasive on the Pacific coast of North America. Individuals of this species altered many floral characteristics in response to insect herbivory—reflectance of the petals, morphology, composition of volatile compounds, nectar and pollen production. If that’s not sufficiently amazing, then consider that the particular floral response varied with the specific insect herbivore. The pollinator fauna shifted too and successfully effected seed production.

These two examples, both from the mustard family, raise interesting questions. They are present-day examples of pollinator shifts; individuals of these two are sufficiently flexible to engage different sets of pollinators under different conditions. By so doing, they may extend their reproductive seasons or overcome some effects of herbivory. What is it about these plants that allows them (but not many others) to do this, and do any other plants do so? Maybe they do—and have yet to be discovered? It’s a fertile area for more research.

Mary F. Willson is a retired professor of ecology. “On the Trails” appears every Wednesday in the Juneau Empire.

More in News

(Juneau Empire File)
Aurora forecast for the week of Nov. 27

These forecasts are courtesy of the University of Alaska Fairbanks’ Geophysical Institute… Continue reading

Rain at the National Weather Service Juneau station on Nov. 11 doesn’t exist as snow until hits the upper portion of nearby Thunder Mountain. So far this November has been both warmer and wetter than normal. (Photo by National Weather Service Juneau)
El Niño playing outsize role in Juneau’s warmer temperatures, according to National Weather Service

Early peek at numbers shows Juneau is 4.9 degrees warmer than average this November.

An emergency rescue vehicle parks in front of the Riverview Senior Living center at midday Monday after resident Nathan Bishop, 58, was discovered in the attic about 40 hours after he was reported missing. (Mark Sabbatini / Juneau Empire)
Nathan Bishop found alive in attic of Riverview Senior Living complex after 40-hour search

Family members say they remain supportive of facility’s locally available assisted living services.

View from the West Ridge at Eaglecrest on Nov. 13. (Photo by Deborah Rudis)
Wild Shots

To showcase our readers’ work to the widest possible audience, Wild Shots… Continue reading

Lisa Daugherty, owner of Juneau Composts!, stands in front of a recently acquired trommel screener, which separates different materials like soil, gravel, mulch and sand. She has invested $250,000 in the company since she started it in 2017. (Meredith Jordan/ Juneau Empire)
Federal dollars for public composting project concerns private-sector operator

Juneau Composts! owner says city project could ultimately shut down business

Charlene Apok leads Data for Indigenous Justice and works with the state’s Maternal Child Death Review to understand maternal mortality in Alaska. Apok analyzed data in their office on Sept. 25. (Photo by Claire Stremple/Alaska Beacon)
Data links Alaska’s sky-high maternal mortality rate to domestic violence

Studies show violence and overdoses cause more deaths than medical problems.

(Michael Penn / Juneau Empire File)
Police calls for Friday, Nov. 24, 2023

This report contains public information from law enforcement and public safety agencies.

(Michael Penn / Juneau Empire File)
Police calls for Thursday, Nov. 23, 2023

This report contains public information from law enforcement and public safety agencies.

(Michael Penn / Juneau Empire File)
Police calls for Wednesday, Nov. 22, 2023

This report contains public information from law enforcement and public safety agencies.

Most Read