Are Colorado’s Columbines Losing Their Spurs?

The Get Out There wildflower guide is all about learning to see how nature works -- about looking for unusual forms of common flowers in order to see evolution in action. The book also underscores the co-evolution of flowers and their (primarily) insect pollinators. This update draws on these themes in describing the spread of an eye-stopping Columbine variant in northern Gunnison County adjacent to the Crystal River watershed.

I was perplexed. In early July, hiking just outside Gothic, I came across colonies of Colorado Columbines that looked like large pansies. Say what?

The deep lavender color looked familiar, but each inflorescence was made up of ten uniformly colored sepals (instead of five alternating lavender petals and white sepals). The flowers also lacked the Columbine’s distinctive, nectar-bearing spurs.

As I continued along the trail, I spotted intermediate forms -- a bloom with a flat pansy face, but with a few spurs. And then I saw a pansy and spur-bearing form of Columbine on the same stalk. A little later, I came across a spurless form that had only white sepals, not all lavender ones.

See my photos below (© 2024 with rights reserved). For comparison, the right hand photo in the first row provides a side view of a standard spur-bearing Blue Columbine.

 Something Is Happening Here

 It all reminded me of that classic line from Bob Dylan’s Ballad of a Thin Man: “[S]omething is happening here…But you don’t know what it is. Do you, Mister Jones?” Indeed, I did not. But I was determined to find out.

 After some research, I learned that spurless purple Columbines had first been reported in 1897 by the pioneering botanist Alice Eastwood. The spurless blooms had been passed on to Eastwood by Colorado resident Anna Dailey; she had collected them near Evergreen in Jefferson County. Hence, this form of Columbine was later named Aquilegia coerulea var. daileyae.

 Over a century later, the daileyae variant continues to flourish in Jefferson County near Rocky Mountain National Park and has also been reported (by Al Schneider of swcoloradowildflowers.com fame ) in the La Plata Mountains between Durango and Cortez. A search of iNaturalist.com indicates that, in recent years, this Columbine mutant has been found in several other Colorado counties east of the Continental divide. There are also two iNaturalist observations of the daileyae variant in Gunnison County, but only one observation of a variant with all white sepals.

 The century-long proliferation of Colorado’s unique daileyae Columbines has attracted the interest of evolutionary biologists. On its face, the variant’s spread seems counter-intutitve. Spurless Columbines lack nectar and thus should be at a significant reproductive disadvantage vis-à-vis the standard form of Blue Columbine. Pollinators typically favor nectar-bearing flowers.

 So why has this mutant form survived so long and begun to appear (and propagate itself) in other parts of Colorado?

 The answer is that the daileyae variant appears less likely to be eaten by local animal foragers. That is one of the main findings of a team of biologists from the University of California at Santa Barbara (UCSB) who conducted extensive field research from 2014-2016 in Jefferson County on the mutant variety of Columbines.

Despite the lack of nectar, the UCSB team found that the daileyae variant has prospered – accounting for roughly 25% of Columbine forms in the study area – because the variant was less likely to be damaged by key herbivores, namely aphids and mule deer. The UCSB scientists also learned that, while spurless Columbines were no longer pollinated by hawkmoths, they were not disfavored by bumblebees, a second major pollinator for Columbines.

 UCSB’s research stresses that the scientific significance of Colorado’s mutant Columbines goes well beyond the daileyae’s strikingly different flowers and unexpected (i.e, non-pollinator-driven) success.

 New species commonly arise through nature’s selection of incremental small changes which lead an organism to be better adapted to different or changing conditions. The reproductive merits of extreme mutations – known as homeotic mutations, where whole structures may be displaced during an organism’s development (e.g., replacing antennas with legs; nectaries with sepals) -- has rarely been documented.

 Hence, in the case of the daileyae variant, we may be watching a unique evolutionary event as the radical change in the structure of the Columbine’s flower – substituting a second set of sepals for the standard “reward-filled” nectar spurs – begins to drive a new pollenation dynamic. As a result, the standard and variant forms of the Blue Columbine may begin to see increasingly divergent sets of pollinators (and, potentially, types of pollen) as well as  different geographical niches. All of which could ultimately lead the daileyae variant to become a new species.

 Nectar spurs have long played a central role in the geographical spread and speciation (known as “adaptive radiation”) of Columbines because the length of spurs (varying from 1 to 12 cm among species) restricts the type of pollinators that visit the flowers. Each spur has a nectar gland at its base, so nectar rewards are efficiently harvested by different pollinators depending on the size of their tongues (proboscis), from bumblebees to hummingbirds to hawkmoths, which have the longest tongues

Thus, different types of spurs – or their absence - may increase or reduce the reproductive isolation of different flower forms. And it is that isolation which typically defines the boundaries between species and drives evolution.

A detailed account of the UCSB’s research can be found at this link. Earlier research on the daileyae variant by University of Colorado biology professor Jeff Mitton can be found here.

Postscript: The Summer 2024 issue of Aquilegia, journal of the Colorado Native Plant Society (CoNPS), includes a precis of the genetic factors responsible for the development of the mutant floral structure that characterizes the spurless variant of Aquilegia coerula.

The article, "Genetic Regulation of Flower Development in Aquilegia coerulea (Colorado Blue Columbine)” by Elizabeth Rose was published after I authored my original post. It is well worth reading for a further introduction to the scientific literature on this subject.