Dandelion Sex, Or The Lack Thereof

Dandelion (From Wikipedia)

I’ve just finished reading Frogs, Flies, & Dandelions: the making of species by biologist Menno Schilthuizen –an engaging and informative book on species formation. Here’s a little taste of what I learned; it illustrates that genetics isn’t perfect, and evolution is beautifully adaptive.

Historically, the common dandelion, that ubiquitous and irritating weed found in gardens and fields throughout North America and Europe, has been a puzzle to botanists. For a long time, no one was sure how many species existed. In the 1700’s, Carolus Linnaeus said only one; in the 20th century, Scandinavian botanists claimed more than two-thousands existed. But with DNA testing, came the answer. Many dandelions are, in fact, clones. In place of normal sexual reproduction with two sets of chromosomes being divided into sex cells, the ovules and pollen, some dandelions reproduce by parthenogenesis, or virgin birth, because at one point in their history they mutated into having three sets of chromosomes, a number which is sexually indivisible. The mutant dandelions instead produce unfertilized –but still viable– seeds, each with a triple set of chromosomes –in other words, a clone.

What’s most illuminating is that the same mutation has popped up several times. So there are several strains with triple chromosomes, all sexually isolated from one another because they can only reproduce by cloning themselves. But it gets better; the clones still produce pollen, except it is completely sterile. Only in the light of evolution does this sordid asexual tale make sense. Why waste the time and energy producing “irregular pollen” if it’s never going to be used? Perhaps god takes a sadistic pleasure in irritating people’s allergies. Or he’s invested heavily in big pharmaceuticals. If so, I hope he had Bernie Madoff sitting on his nest egg.