Tuesday, December 23, 2008


The following I got from my reading this morning over at the Border's Books near our new condominium. I walked over because my car is snowed in and I don't have a snow shovel. We left our snow shovel back in Spokane at the house we sold there. The new owner is getting a lot of use out of it, no doubt, but we could use it here, where Vancouver is experiencing near record snowfall. Anyhow, evolution has certainly developed many unique ways to foster reproduction. I found this one in Stephen J. Gould's The Panda's Thumb:

Consider the curious life of a male mite in the genus Adactylidium, as described by E.A. Albadry and M.S.F. Tawfik in 1966. It emerges from its mother's body and promptly dies within a few hours, having done apparently nothing during its brief life. It attempts, while outside its mother, neither to feed nor to mate. We know about creatures with short adult lives—the mayfly's single day after a much lengthier larval life, for example. But the mayfly mates and insures the continuity of its kind during these few precious hours. The males of Adactylidium seem to do nothing at all except emerge and die.

To solve the mystery, we must study the entire life cycle and look inside the mother's body. The impregnated female of Adactylidium attaches to the egg of a thrips. That single egg provides the only source of nutrition for rearing all her offspring—for she will feed on nothing else before her death. This mite, so far as we know, engages exclusively in sib mating; thus, it should produce a minimal number of males. Moreover, since total reproductive energy is so strongly constrained by the nutritional resources of a single thrips' egg, progeny are strictly limited, and the more females the better. Indeed, Adactylidium matches our prediction by raising a brood of five to eight sisters accompanied by a single male who will serve as both brother and husband to them all. But producing a single male is chancy; if it dies, all sisters will remain virgins and their mother's evolutionary life is over.

If the mite takes a chance on producing but a single male, thus maximizing its potential brood of fertile females, two other adaptations might lessen the risk—providing both protection for the male and guaranteed proximity to his sisters. What better than to rear the brood entirely within a mother's body, feeding both larvae and adults within her, and even allowing copulation to occur inside her protective shell. Indeed, about forty-eight hours after she attaches to the thrips’ egg, six to nine eggs hatch within the body of a female Adactylidium. The larvae feed on their mother’s body, literally devouring her from inside. Two days later, the offspring reach maturity, and the single male copulates with all his sisters. By this time, the mother’s tissues have disintegrated, and her body space is a mass of adult mites, their feces, and their discarded larval and nymphal skeletons. The offspring then cut holes through their mother's body wall and emerge. The females must now find a thrips’ egg and begin the process again, but the males have already fulfilled their evolutionary role before "birth." They emerge, react however a mite does to the glories of the outside world, and promptly die.

Gould in the brief essay which includes the snippet above is talking about why almost all sexed species produce males and females at about the same 50/50 ration. The
Adactylidium mite is the exception that tests the rule.

1 comment:

Thomas J. Brown said...

The new owner probably is getting a lot of use out of it, but I hope he has a snow blower too!

I was going to try to be green this winter and shovel the whole time. I thought, "Spokane never really gets a lot of snow, it'll be fine."

Not this year.

And after doing the research, it turns out that the snow blower I want usually sells out in October.

The best laid schemes, eh?