The Duck Penis (and Vagina), Part II: Fowl Designs

The Duck Penis (and Vagina), Part II

After reading the title of this post you might object, “But Richard this is duck penis month! Why let the duck vagina share the spotlight, too?” Well,  it was a tough editorial decision, but after steeping myself in Prof. Brennan’s work on duck genitalia for the last few weeks I have come to undeniable conclusion that I cannot make the duck penis explicable without at least some discussion the duck vagina as well.

In this undertaking, I ask you to please bear with me, dear reader, because despite being an expert in penis science, Franz Liszt studies, and food/wine pairings, “vagina science” is entirely virgin territory for me. But if my mentor Tad Everhard taught me one thing it is to never be afraid of the unknown.

The Duck Vagina

Let’s start with the basics. First, the vagina, in my understanding, is best defined as where the penis goes.  Say you’re studying a certain penis and the literature makes reference to copulation or intromission, then the vagina is where the penis is during this time. Typically it is located on the female where the penis would be in the male, but “reflected” inside her body like an inverted penis. Or, no–it’s more like if you were to wrap one long penis around another penis, then remove the inside penis, that’s basically a vagina.

Does that make sense? Is any of this making sense right now?

*sigh*

Honestly, this is going to be even harder than I thought. The few things I know–or used to know–about vaginas I learned in grad school decades ago. Maybe if I revisit my old notes they’ll help me to get my bearings.

So, I apologize, but a full account of the evolution of the duck penis will have to wait until I can get a grapple on this slippery “vagina science.” In the meantime I can still give a descriptive account of the duck penis and its basic functionality, which I assure you is fascinating in its own right.

Duck Penis Anatomy and Erections

Anatomists describe the duck penis as an “out-pocketing” of the wall of the duck’s cloaca, which is the bird’s multi-purpose hole for the urinary, intestinal, and reproductive tracts. Curiously, the penis is connected lymphatic system rather than the vascular system like in mammals; that is, duck erections are powered by lymph, not blood. Also unusual is that normally the penis is held inverted inside the duck abdomen “outside-in”, and males do not display their penis prior to copulation (Brennan et. al 2010) .

This is unfortunate, because a duck erection is truly a sight to behold. After the duck mounts the female to copulate, the erect duck penis emerges–nay, explodes–into the female reproductive tract, spiraling out of the male in a corkscrew shape like the contrail of a sidewinder missile. This all occurs in under half a second, during which the duck penis can reach velocities of up to 1.6 m/s (3.6 mph)!  Ejaculation soon follows: semen rushes out from the base of the penis and follows a recessed groove along the outside of the penis until it cascades off the tip. The penis then inverts itself back inside the male, as if nothing ever happened. See the duck erection for yourself in the video below from Brennan et. al (2010):

Duck Penis Diversity — An Evolutionary Puzzle

Perhaps even more astounding–and puzzling–is the sheer diversity of duck penises. Between species the length of the erect penis ranges from 2.5 cm in the Common Goldeneye to up to 42.5 cm in the Argentine Lake Duck (Coker et al. 2002, McCraken et. al 2001).

Array of duck penises

Diverse array of duck penises. Left-to-right: Harlequin duck penis, African goose penis, Long-tailed duck penis, Mallard penis. Figure adapted from Brennan et. al (2007).

And many duck penises are elaborated with various spines, barbs, knobs, ridges, grooves, and other ornaments (yes, ducks belong the barbed penis club along with cats, most primates, and many other mammals and reptiles, too).

Argentine Lake Duck penis and spines

Left: Everted penis of the Argentine Lake Duck. Right: Close-up of the spines and ridges of Argentine Lake Duck penis (McCraken 2001).

What can account for this wild variability among duck penises? For instance, what is the purpose of the seemingly gratuitous half-meter penis in the Argentine Lake Duck? Do female ducks simply prefer longer and more ornamented penises, and hence choose mates with them? Or is it some form of sperm competition between males which is driving the evolution of more powerful sperm-displacing penises?

Or maybe the causal mechanism lies so far outside the current accepted framework of evolutionary penis science that most researchers could not even conceptualize it, like black holes before the theory of general relativity.

Stay tuned, dear reader, for the surprising conclusion in my last installment on the duck penis (and vagina).

References

Brennan, P. L., Prum, R. O., McCracken, K. G., Sorenson, M. D., Wilson, R. E., & Birkhead, T. R. (2007). Coevolution of male and female genital morphology in waterfowlPLoS one2(5), e418.

Brennan, P. L., Clark, C. J., & Prum, R. O. (2010). Explosive eversion and functional morphology of the duck penis supports sexual conflict in waterfowl genitaliaProceedings of the Royal Society B: Biological Sciences277 (1686), 1309-1314.

Coker, C. R., McKinney, F., Hays, H., Briggs, S. V., & Cheng, K. M. (2002). Intromittent organ morphology and testis size in relation to mating system in waterfowlThe Auk119(2), 403-413.

McCracken, K. G., Wilson, R. E., McCracken, P. J., & Johnson, K. P. (2001). Are ducks impressed by drakes’ display?Nature413(6852), 128. (pdf)

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