the world is awash in sperm

The Navanax sea slug is a sort of legend in its own lifetime according to zoologist Janet Leonard. It’s known as the “if you can’t eat it, mate with it” slug.

Navanax is a hermaphrodite: like many other species, it has the anatomy and the ability to be either male or female. And Navanax gets to choose between the genders over and over again–it never has to settle for one or the other.

The name of the mating game, after all, is to pass along the most DNA, and sperm cells, which are small, require far less energy to make than do the much larger eggs. Eggs are expensive, but the world is awash in sperm, says evolutionary biologist Eric Fischer. Accordingly, females make many fewer eggs than males make sperm. And while males try to spread their inexpensive, abundant sperm far and wide, females try to invest their precious and limited store of eggs carefully.

Janet Leonard has been peeping in on and videotaping Navanax sex for more than a decade now. And, she reports, it’s a curious affair. Every Navanax comes equipped with a penis on the right side of its head; a few inches behind is a genital slit that leads to an ovary. Mating begins when one slug follows the trail of another and comes up from behind. The first slug pokes its head under the other’s tortilla of skin, twisting around to position its penis near the other’s genital opening. The second slug responds to this courting by raising its tail and unwrapping the sheath of skin around its body. After the sperm has passed from the first animal to the other, the female swings around and begins nudging its penis toward the genital slit of the male. If all goes well, they exchange jobs.

The animals keep trading roles, four, five, or more times. Fittingly, it’s a sluggish affair. One round of copulation, Leonard sighs, can take five hours. One of the first things you learn working with these animals is patience.

Often chains of three or more mating animals will form with those in the middle acting as male and female simultaneously.

This is a video of a Navanax biting an Aplysia, not having sex. I’ve included it because the two researchers making the video get so damn excited… “Hold on, Lafonda… this is a beautiful thing… atta girl”

Published in: on March 8, 2010 at 7:12 am  Comments (37)  
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