I’ve written before about “bee-mimicking orchids,” whose petals have evolved into a shape roughly resembling that of a female bee or wasp. Randy male hymenopterans, lured by the shape (they can’t see very well), and, I believe, by the flower’s fragrance—which in some cases has also evolved to resemble insect pheromones—land on the flower and try to copulate with it. They fail, of course, but during their fornicatory struggles the flower’s pollinia (sacs of pollen) detach from the flower and affix themselves to the insect’s head.
The frustrated insect flies away, but not long thereafter is fooled again by another flower of the same species. When it lands and tries to copulate again, the pollinia from the previous flower are transferred to the new orchid and pollinate it. In this way flowers have evolved to use the insect as a sort of flying penis, a way to effect pollination through trickery. Here’s a short video in which David Attenborough shows how it works:
Today’s xkcd describes such an orchid, Ophrys apifera, which is found throughout Europe. The kicker here is that, according to the comic (but see below), the pollinator has gone extinct, though its appearance can still be discerned through the appearance of the flower. Since there’s no insect around to pollinate it, the flower has evolved self-pollination (that is, those individuals that were able to self-pollinate were the only ones to pass their genes to the next generation).
It’s a nice story, and the part about the extinct pollinator and the evolution of self-pollination is probably true, but I’m not sure one can discern the appearance of the extinct pollinator from the flower’s appearance. The Orchids Wiki notes this:
The flowers are almost exclusively self-pollinating in the northern ranges of the plant’s distribution, while pollination by the solitary bee Eucera occurs in the Mediterranean area. The sepals are marginal and spread out, coloured mauve to pink, often with a greenish central line. The flower lip is furry to the touch and is quite variable in the pattern of coloration, but is usually brownish-red with yellow markings.
The pollinia are produced on the inner face of a greenish column overhanging the lip, ready to deposit the pollen on visiting bees. Eucera bees in the past have influenced the evolution of bee orchids. Male bees, over many generations of cumulative orchid evolution, have favoured plants with the most female-bee-shaped lip through trying to copulate with flowers, and hence carrying pollen.
The flowers have a generalized shape, and I’m not sure whether individuals of O. apifera in southern Europe, where they mimic an extant insect, differ in appearance from those in the northern part of the range, where they’re self-pollinated and supposedly resemble a “ghost insect.” If they don’t differ, then we can’t say, as the cartoon does, that the shape of flowers in, say, England tells us something about the appearance of the extinct pollinator. There must be work on this, but I don’t know of it.
It would also be worth studying whether the northern flower still retains a hymenopteran-like fragrance and, if so, whether it differs from the fragrance of southern flowers that attract Eucera bees.
Regardless, today’s xkcd is poignant, and does impart a nice lesson about biology and evolution.
h/t: David, infiniteimprobability