Tuesday, January 01, 2008

Promiscuity: An Evolutionary History of Sperm Competition Chapter 2

I recently recommended Dr. Tatiana's Sex Advice to All Creation to someone and was reminded that I had Promiscuity waiting for me on the shelf upstairs. Over the next few posts I'll jot down a few notes and afterwards boil those down for your perusal along with a few of my personal observations. It should be noted that these posts will likely be extraordinarily graphic and thus not recommended for the faint of heart. That said, they should at least be interesting but don't expect it to hang together like a proper narrative since I'm just going over my notes, not retyping the whole text.

Chapter 2

Birds, it turns out, are total sluts. Studies indicate that 70% of bird species engage in sex outside their brooding partnership. A notable example is the purple martin; when given access to a multi-apartment birdhouse in the spring, the entire house will be first taken over by one male who will protect it fiercely until he attracts a mate. Once he has his mate in place and she's attending her nest he'll invite other males to join the household and when they do so he'll also have his way with their mates as well. Genetic studies show that the dominant male in fact fathers half the offspring in the entire complex. The amount of sluttiness (and the success of it) seems to be directly related to just how different the males look from the females. Apparently females need a particularly studly-looking guy to make it worth the effort.

On the flip side, monogamous females are relatively rare and when they do occur it's usually under somewhat unusual circumstances. Among some insect species which reside in dormancy underground before sexual maturity, males will actually dig up dormant females and copulate with them before they are fully developed. Some butterflies even go so far as to have a long, hard penis which can penetrate the female's pupal casing. Even more bizarrely, female angler fish support their tiny male counterparts for life. The male lodges himself inside the female and sucks her blood to stay alive ready at any moment to perform his function.

The Corydoras Catfish takes no chances with the father of her children. When mating the female places her mouth directly over the male's genitalia, sucks his sperm out and reissues it through her own genitalia seconds later to fertilize her eggs. Male seahorses and pipefish are similarly cautious since responsibility for the eggs lies with them. The female lays her eggs in the male's brood pouch and only after the eggs are secure does the male fertilize them by himself with a box of tissue and some hand lotion.

While the female is out seeking the attentions of others the male is working on a plan of his own to keep her faithful. The most common of these is 'mate guarding.' In many species the male will simply follow the female wherever she goes when he senses she is fertile. For insects, the last male to copulate with a female has an advantage over those who have come before so they tend to guard their females after the act. One extreme is the male dungfly who will hang on his mate's back for 20 minutes while she lays her eggs to ward off any latecomers. Alternatively, some species of shrimp have reproductive processes which favor the first male to copulate with a female. Males range far in wide in search of virgins and in some cases will go so far as to pick up an immature female and carry her around for several days until she's ready to be fertilized. Depending on the male to female ratio a male may cart around a woman for 9 whole days before he has his way with her and leaves her forever.

If a male can't guard his mate he may resort to just doing it with her over and over again. Giant water bugs have been known to copulate 100 times in 36 hours during periods of egg laying. Birds may do the act from 1 to 500 times over a single clutch of eggs.

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