Flower petals show evolution at cell’s level

UC SANTA BARBARA (US) — A new study of flower petals shows evolution in action, and contradicts more that 60 years of scientific thought.

Columbine flowers, known as Aquilegia, evolved several lengths of petal spurs that match the tongue lengths of their pollinators, including bees, hummingbirds, and hawkmoths. The petal spurs are shaped like a tubular pocket and contain nectar at the tip. The spurs grow from 1 to 16 centimeters in length, depending on the species.

Researchers discovered that longer spurs result from the lengthening of cells in one direction, called anisotropy, and not from an increased number of cells. This finding contradicts decades of scientific thinking that assumed the elongated petals form via continued cell divisions.


Hawkmoth pollinator visiting an Aquilegia flower. (Credit: Scott A. Hodges)

Scientist from the University of California, Santa Barbara, and Harvard University report their findings in the Proceedings of the Royal Society B.

“When we went in and looked at this in detail, we found that even the super-long-spurred flower doesn’t differ much in cell number from the short-spurred one,” says Scott A. Hodges, a professor in the ecology, evolution, and marine biology department at UC Santa Barbara.

Most studies of shape, particularly of leaves and of some flower parts, have focused their attention primarily on genes controlling cell division, says Hodges. “What this study is saying is that you don’t want to just look at those kinds of characteristics; here’s this whole other way to produce a tremendous amount of shape diversity without involving cell divisions,” he adds.

In long-spurred plants, the spurs reach the same length at the same point in time as the short-spurred flowers, but they keep on growing, says Hodges. The rest of the flower has to wait for the spurs to lengthen.

Until then, the pollen can’t be released and the ovules are not ready to be fertilized. The flower has to stop that part of development while the spurs grow. Then, almost a week later, those flowers become reproductive, after the spurs have grown longer.

The evolution of petal spurs in columbines is considered a textbook example of adaptive radiation. Like Darwin’s finches, over time, the columbines evolved a variety of species to exploit different ecological niches. The short-spurred columbines can be easily pollinated by bees. Hummingbirds have long beaks and tongues and can pollinate flowers with spurs of medium length. Hawkmoths have very long tongues and can pollinate columbines with the longest spurs, such as Aquilegia longissima.

More news from UC Santa Barbara:

chat15 Comments


  1. Roy Niles

    It seems this is more evidence that forms are changed due to strategic necessities rather than by more simplistic neo-Darwinian conceptions.

  2. Andrew Feinberg

    Feel free to explain the difference.

  3. Roy Niles

    Strategic functions adapt to new environments and find ways to engineer their forms to follow. Forms don’t just up and divide and conquer and find a function to fit. Accidents are taken advantage of rather than being relied on to give advantage.

  4. Andrew Feinberg

    Okay. You just described evolution or, possibly, a way in which “forms are changed due to strategic necessities”. So which one was that and how does it differ from the other?

  5. Roy Niles

    Read the article again and then read papers on adaptive mutation, etc. Then decide for yourself how things must likely work.

  6. Dr. O'

    OK, which came first, the long spir or the bee, hummingbird and/or the moth?

  7. Roy Niles

    It doesn’t matter which came first, since each has a strategy that interacts with another’s strategy. Physical forms of each “interchange” accordingly..

  8. pltguy

    Actually it does matter. Previous work has shown that the spurs evolved much later than the pollinators tongues. Thus the plant’s spurs have evolved to match the tongue length. Nothing non-Darwinian is necessary to explain this. That is, plants with spurs that most closely match the tongue-length of their frequent visitors will receive the most pollination and high-fitness reproduction. Pretty simple in fact.

  9. Roy Niles

    You left out the part where the pollinator’s tongues evolved earlier to anticipate the changes in the spurs. There is a process of strategic anticipation in evolution, which is also pretty simple once you understand it.

  10. pltguy

    that’s not correct. The pollinator’s tongues may have evolved for may other reasons. Being a bigger mothe may have advantages for many other reasons, causing the tongue to be longer too. The moth may have evolved to fit the spur/tube length of other flowers previously and then the columbine inhabited the range of the long-tongues moth. Then the flower evolved to fit the pollinator’s tongue. There’s no need to conjure up a “strategic anticipation” as you suggest.. Simple advantages of random mutation are all that’s “needed” to understand this process.

  11. Roy Niles

    Tongues may have evolved for other reasons, but coincidence is often a factor. I didn’t conjure up anticipation – it’s a well known field of study in evolutionary biology – except to those of you who wish to remain ignorant.. There is no such thing as simple random mutation of strategies, except in your neo- Darwinist rationalizations..

  12. Andrew Feinberg

    Roy, either anticipatory evolution isn’t as well known as you make it out to be, or it’s lacking in scientific credibility. I’m pretty sure it’s both. Feel free to provide us with some examples or something. Maybe a link, I dunno.

  13. Roy Niles

    Also you should be aware of preadaptation as a well documented phenomenon.

  14. Chispa Loro

    Uh, Roy – that link is to books about soft computing. Are you now proposing that nature models itself on computer science? I’ve long been suspicious of computer modeling to explain nature – the reverse is even worse. I think plt guy and Andrew have presented a more coherent (cogent too) statement about the relationship between the spur length and the pollinators’ tongues. The tongues have other functions for the animal in addition to acquiring nectar and so are subject to other evolutionary pressures (getting water from deep in cracks, plant apices etc). The columbine’s spurs don’t do anything except disperse nectar and aren’t influenced by other purposes. Except there may be a strategic advantage in a plant population of mixed species (assuming spur length is species-specific) for all flowers to not be ready for pollination at the same time. So different spur lengths influence how long it takes for the flowers to be ready to release pollen. This gives the population an advantage in case pollination and fertilization conditions aren’t optimum at the time the short-spur plants are releasing pollen. I like this view because it shifts from the selfish gene concept (species survival) to a larger-scale survival of the genus. None of that has anything to do with the study tho, as the study is discussing HOW the spurs grow longer not why.

  15. Roy Niles

    If you clicked the link, you’d find this:
    Anticipation: Why is it a subject of research?
    Anticipation occurs in all spheres of life. It complements the physics of reaction with the pro-active quality of the living. Nature evolves in a continuous anticipatory fashion targeted at survival. The dynamics of stem cells demonstrate this mechanism. Through entailment from a basic stem cell an infinite variety of biological expression becomes possible.
    Sometimes we humans are aware of anticipation, as when we plan. Often, we are not aware of it, as when processesembedded in our body and mind take place before we realize their finality. In tennis, for example, the return of a professional serve can be successful only through anticipatory mechanisms. A conscious reaction takes too long to process. Anticipation is the engine driving the stock market. Creativity in art and design are fired by anticipation.
    “The end is where we start from,” T. S. Eliot once wrote. Before the archer draws his bow, his mind has already hit the target. Motivation mechanisms in learning, the arts, and all types of research are dominated by the underlying principle that a future state—the result—controls present action, aimed at success. The entire subject of prevention entails anticipatory mechanisms.

We respect your privacy.