Natures wonders: some bird sex organs are weird (Introduction)

by David Turell , Friday, April 01, 2022, 01:48 (966 days ago) @ David Turell

Three percent of birds have complex sex organs:

https://www.smithsonianmag.com/science-nature/why-have-female-animals-evolved-such-wild...

"Ninety-seven percent of all bird species have no phallus. Those that did, including ostriches, emus and kiwis, sported organs quite different from the mammalian variety. Corkscrew-shaped, they exploded out into the female in one burst, and engorged with lymphatic fluid rather than blood. Sperm traveled down spiraling grooves along the outside.

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"But she knew there was no way an appendage as complex and unusual as the duck penis would have evolved on its own. If the penis were a long corkscrew, the vagina ought to be an equally complex structure.

"The first step was to find some female ducks. Brennan and her husband drove out to one of the surrounding farms and purchased two Pekin ducks, which she euthanized without ceremony on a bale of hay. (Brennan’s husband is used to these kind of excursions: “He brings me roadkill as a nuptial gift,” she says.) Instead of slicing the reproductive tract up the sides, she spent hours carefully peeling away the tissues, layer by layer, “like unwrapping a present.” Eventually, a complex shape emerged: twisted and mazelike, with blind alleys and hidden compartments.

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"By carefully dissecting the genitals of 16 species of waterfowl, Brennan and her colleagues found that ducks showed unparalleled vaginal diversity compared to any known bird group. There was a lot going on inside those vaginas. The main purpose, it appeared, was to make the male’s job harder: It was like a medieval chastity belt, built to thwart the male’s explosive aim. In some cases, the female genital tract prevented the penis from fully inflating, and was full of pockets where sperm went to die. In others, muscles surrounding the cloaca could block an unwanted male, or dilate to allow entry to a preferred suitor.

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"Whatever the females were doing, they were succeeding. In ducks, only 2 to 5 percent of offspring are the result of forced encounters. The more aggressive and better endowed the male, the longer and more complex the female reproductive tract became to evade it. “When you dissected one of the birds, it was really easy to predict what the other sex was going to look like,” Brennan told the New York Times. It was a struggle for reproductive control, not bodily autonomy: Although a female couldn’t avoid physical harm, her anatomy could help her gain control over the genes of her offspring after a forced mating.

"The duck vagina, Brennan realized, was hardly the passive, simple structure that biologists had made it out to be. In fact, it was an expertly rigged penis-rejection machine. But what about in other animal groups?

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"What they found at first reminded them strongly of the duck story. In the harbor porpoise, for instance, the vagina spiraled like a corkscrew and had several folds blocking the path to the cervix. Porpoise penises, in turn, ended in a fleshy projection, like a finger, that seemed to have evolved to poke through the folds and reach the cervix. Just as in ducks, it seemed that males and females were both evolving specialized features in order to gain the evolutionary advantage during sex.

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"What she found in dolphins gave her pause. The substantial clitoris before her was a hint at something that seems obvious, but often isn’t: sex isn’t just for reproduction.

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"Today, we know that genitalia do far more than just fit together mechanically. They can also signal, symbolize and titillate—not just to a potential mate, but to other members of a group. In humans, dolphins and beyond, sexual behavior can be used to strengthen friendships and alliances, make gestures of dominance and submission, and as part of social negotiations like reconciliation and peacemaking, points out evolutionary biologist Joan Roughgarden,

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"Focusing solely on a few dramatic cases of sexual conflict—the “battle of the sexes” approach—obscures some of the other powerful forces that shape genitals. Doing so risks leaving out species in which the sexes cooperate and negotiate, including monogamous seabirds like albatrosses and penguins, and those in which homosexual bonds are as strong as heterosexual ones. In fact, it appears that the stunning variety of animal genitals are shaped by an equally stunning variety of driving forces: conflict, communication, and the pursuit of pleasure, to name a few."

Comment: So it is not just two by two up Noah's gangplank. These arrangements give some animals a sexual choice of mate. But not all. In domesticated beef cattle the cow goes into heat and wants someone, anyone quick. Vagina and penis are just like ours, so we might have changed them from what happens in the wild. The photos in the article show amazingly complex shapes. Look at them. Were they designed for the purpose of selection?