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    Evolution in Your Own Backyard
    By Enrico Uva | October 10th 2011 07:45 AM | 2 comments | Print | E-mail | Track Comments
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    About Enrico

    After majoring in chemistry at Concordia University I worked briefly at Fisheries and Oceans' Arctic Biological Station and in the food industry...

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    It may be more of a case of inadvertent artificial selection rather than natural selection, but weed picking and lawn mowing may be changing the nature of dandelions in our lawns. There are a variety of root lengths among dandelions. If you succeed in completely removing a plant down to its root tip, it will not be able to grow back or flower or reproduce. The longer the root, the less likely it is that the plant will meet such a fate. Since dandelions can regenerate themselves from a root fragment, eventually those with longer roots will leave more offspring and become more common than the shorter rooted variety. That could explain the ridiculously long root I dug up this weekend. It's not apparent in the picture, but the tip from the longer one still remained underground.

    Shorter stemmed flowers also have a selective advantage as they escape the cutting action of the lawn mower, and there's no doubt that the typical dandelion in a lawn is shorter-stemmed than those that grow in unattended fields.



    Comments

    Gerhard Adam
    There may some element of truth to this, but it seems unlikely that our lawns are sufficiently closed to elicit much in terms of direct selection pressure.

    In fact, it seems more probable that if a plant is pulled out and the root tip remains, that new growth will use that as a starting point and grow up as well as down.  Therefore, the more you tend to pull up plants and leave a tip behind, the longer the root will eventually become.  Just as the example you showed, I would expect that next year the plant will have even longer roots since the tip remained behind (at a greater depth already).

    Just a thought.
    Gerhard Adam | 10/10/11 | 12:18 PM
    UvaE
    It's a good alternate explanation. But given that the soil layer in many lawns is so thin(including mine), I would imagine that most of the root fragment's subsequent growth would occur upward. Especially since  the root has limited energy reserves, it would be to its advantage to surface as soon as it can. That's not to say that more downward growth won't occur afterwards.

    To test the idea, I would have to collect seeds from long-rooted dandelions. Since they are curiously produced asexually in this species, measuring the root length of the subsequent generation would reveal whether any selection has really taken place.
    There may some element of truth to this, but it seems unlikely that our lawns are sufficiently closed to elicit much in terms of direct selection pressure.
    In urban areas, as the unattended areas have become increasingly scarce, lawns may have become closed enough to succumb to selection pressures.
    Enrico Uva | 10/10/11 | 14:43 PM