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No “Hopeful Monster,” Flower Demonstrates Evolution by Subtraction

Photo: Colorado blue columbine, by Tranquiligold Jin, via Flickr (cropped).

The state flower of Colorado, the Colorado blue columbine (Aquilegia coerulea), is no monster. It is one of the loveliest of wildflowers, with long spurs on its five petals gathered around its nectar-bearing center like a flock of doves (thus its common name “columbine” — dovelike). Some 60 species of Aquilegia live throughout the West. They come in various colors and sizes, usually small and red in California but most often large and pale blue in Colorado. Other species can sport purple, pink, and yellow shades.

Once upon a time, the doves on a Colorado blue columbine flew away; and therein lies a Darwin story.

Something Peculiar about Columbines

Evolutionary biologists at the University of California, Santa Barbara, noticed something peculiar about the columbines in a region of Colorado: some had lost their dove-like petals. About one-fourth of them lacked the nectar-bearing petals and spurs, but bore two sets of sepals, which had turned blue. Astonished, Scott Hodges and Zachary Cabin described them as monsters! The question now was whether they were “hopeful monsters” or “hopeless monsters.” In news from UCSB, reporter Harrison Tasoff declared the answer: the headline, “A Hopeful Monster,” shows a picture of the two varieties of columbine side by side and announces, “Scientists describe an elusive example of abrupt evolution happening in columbines.” This brings Charles Darwin into the story.

When Charles Darwin first codified the theory of evolution by means of natural selection, he thought of it as a gradual process. “We see nothing of these slow changes in progress, until the hand of time has marked the long lapse of ages,” he wrote in his seminal work, “On the Origin of Species.”

But Darwin didn’t have the full picture. “Evolution doesn’t necessarily take all these small changes like Darwin proposed,” said Scott Hodges, a professor in UC Santa Barbara’s Department of Ecology, Evolution, and Marine Biology.

Hodges, doctoral student Zachary Cabin and their colleagues just have identified a case of a sudden evolutionary change. [Emphasis added.]

From the photo of the mutant columbine next to the wild-type flower, one would agree that they “are so different that a taxonomist might assign them to different genera at first glance.” And yet they persist in the area alongside the wild-type flowers.

“Well, well,” Michael Behe might be thinking, “another example of Darwin Devolves: evolution proceeds by breaking things.” Evolution by subtraction, once again. No new genetic information emerges, Stephen Meyer would likely notice. That is all true, but let’s watch the surprised evolutionists argue that this is an example of evolution in action — a big change happening right before our eyes!

drastic change caused by a mutation in a single gene. The finding adds weight to the idea that adaptation can occur in large jumps, rather than merely plodding along over extended timespans.

Jonathan Wells might perk up at a mention of an icon of evolution:

APETALA3-3 is a type of homeotic gene, one that specifies the development of an entire organ. A mutation in one of these genes can have a drastic effect on an organism’s morphology. For instance, one homeotic mutation causes a fly to develop legs where it should have antennae. “Most of the mutations of this nature are going to be like that, just awful,” Hodges continued. “The animal won’t have any chance of surviving. Biologist Richard Goldschmidt called them ‘hopeless monsters.’”

The authors also point to other “classic examples of evolution, such as the pepper [sic] moth (Biston betularia) and pocket mice (Chaetodipus intermedius).” Score two hits for Zombie Science.

Rapid Evolution by “Saltation”?

But as Goldschmidt went on to say, some monsters can be “hopeful.” A dinosaur might lay an egg and see a bird hatch out of it. The possibility of rapid evolution by “saltation” flies in the face of Darwin’s theory, but look — it happened in Colorado! A case of “surprising selection” allows these monster flowers to thrive alongside the wild type. This was worth a write-up in Current Biology. See, “Non-pollinator selection for a floral homeotic mutant conferring loss of nectar reward in Aquilegia coerulea.”

Spurlessness, we learn, is not uncommon, but it seems to have “stuck around in this area.” Can Zachary Cabin really make such a philosophical leap from this instance to evolution in general?

Ever since the theory of evolution was put forward, biologists have debated whether it always occurs in small, gradual steps over long timespans or sometimes as an equilibrium punctuated by abrupt changes.Often, large morphological changes appear within short geologic timescales where intermediate forms may not have fossilized. The question then remains whether many small changes occurred in a short period of time, or perhaps whether single large-scale mutation might be responsible. So, researchers really have to catch the development in action if they hope to build a case that sudden changes can drive evolution.

And so this case gives a hopeful grad student something to publish. He will undoubtedly have a bright future ahead in academic coffee lounges. But did he witness evolution creating something new, novel, or innovative? Was any new information added to the Aquilegia genome? His advisor says:

“This finding shows that evolution can occur in a big jump if the right kind of gene is involved,” Hodges said. APETALA3-3 tells the developing organ to become a petal. “When it’s broken, those instructions aren’t there anymore, and that causes it to develop into a completely different organ, a sepal,” he explained.

Darwin Devolves, Just Like Behe Said

But then, how could the wild-type columbine evolve by a process that removes instructions? 

The team discovered five versions, or alleles, of APETALA3-3only one of which codes for a petal with a functional nectar spur. The other four were broken, as Hodges put it. They also determined that spurlessness is a recessive trait. The flower will develop normally as long as the plant has one copy of the functional allele. But any two of the mutant alleles together will prevent this.

This should indicate that it’s much easier to break instructions than build them. That lesson, however, was lost on Cabin and Hodges. To them, this was an example of evolution in action!

Cabin monitored which insects pollinated the mutants, and which deer and caterpillars ate them. No clear trends were found, though it appears that the predators prefer the intact spurred plants. 

The team was a bit surprised that the usual pollinators, hawkmoths, could not get the “nectar reward” in the mutants they should expect. Maybe the mutants gain a fitness advantage from not having to invest the extra cost of making nectar, he reasoned. Bumblebees, another pollinator, go for the pollen, which still exists in the mutant flowers. Overall, the mutants still get pollinated, and seem to gain another selective advantage by predator avoidance. Presumably this means that the mutants will continue to exist as a separate variety. But has the origin of species been observed?

Although we cannot know for sure whether the d mutant will ultimately result in speciation, comparative studies show multiple plant lineages are associated with the loss of nectariferous petals….

Darwinism by Subtraction 

If loss of information is the way evolution proceeds (and they give other examples within this plant’s family), then Darwinism should proceed by subtraction: “these examples show that loss of nectariferous petals can be an evolutionary stable and successful transition.”

In summary, we have described a clear example of a homeotic mutant that confers a major morphological shift (petal-to-sepal transition) and that has been under positive selection largely due to non-pollinator selection (herbivory avoidance and resource allocation). In addition, the radical change in floral morphology alters pollination dynamics causing a degree of assortative mating that could ultimately promote speciation. As such, these findings fit well into the concept of a “hopeful monster” coined by Goldschmidt where major morphological shifts that delineate taxa arise in a single step.

The only “positive selection” here came about by a functional loss. One cannot get a Colorado blue columbine by a series of subtractions. Ironically, the ones really vindicated by this study are not Darwin and Goldschmidt, but Behe, Meyer, and Wells.