National Geographic

The Alligator Has a Permanently Erect, Bungee Penis [Video]

In the video above, Brandon Moore from Louisiana Tech University is dissecting a freshly dead male alligator. You’re looking at the creature’s underside, near its hip area. As the sequence begins, Moore’s scalpel touches the alligator’s pelvic nerve. The metal makes the nerve fire and… well… just watch the video.

That’s the alligator’s penis—ten centimetres long, ghostly white, and surprisingly quick-moving. It flips out in an instant and just hangs there for a few seconds to greet a startled Moore, before twanging back inside just as quickly. I love that Moore back-steps and freezes. There’s no audio. I wish there was audio.

The video was a revelation to Diane Kelly from the University of Massachusetts, and the key to interpreting the utterly bizarre penis of the American alligator. Here are the highlights: it’s permanently erect; it shoots out like toothpaste from a tube; and it bounces back because it basically has a rubber band attached to it. “It is really weird,” says Kelly. “Really weird.”

That’s not something she’d say lightly. Animal penises are her speciality. She has studied and dissected the male organs of mammals and turtles to better understand their anatomy and their evolutionary history. Meanwhile, her close colleague Patricia Brennan—“the other penis lady”—had done a lot of work on birds, snakes and lizards (remember the infamous duck penis video?). The crocodilians—crocodiles, alligators and their kin—seemed like the obvious group to target next.

Here’s what we knew about their penises before Kelly started. The males have a single large phallus stashed within the cloaca. That’s the joint opening you can see in the video above, which also gives way to the urinary and digestive tracts. Sperm travels along a deep groove running the length of the penis, which is surrounded by dense tissue. Okay, but how does a crocodilian inflate its penis or eject it from the cloaca?

To find out, Kelly needed to get her hands on some crocodilians. Fortunately, she didn’t have to work with living ones. In September, she headed down to the Rockerfeller Wildlife Refuge in Louisiana, which has an annual cull to control the local population of American alligators. They let her work with four of the animals that had been shot, including a huge four-metre-long bull. “It was really scary, even though it was dead!” says Kelly.

Through dissection, she discovered that the alligator’s penis doesn’t inflate at all. It’s permanently erect. The whole structure is filled with dense layers of a stiff protein called collagen. Even the central bit, where blood would normally flow down, is just collagen, collagen and more collagen.

That’s bizarre. Whenever a reptile, bird or mammal has a penis (and some don’t), it always inflates in some way. Maybe blood pumps into it, as in humans, other mammals, and turtles. Maybe it explosively turns inside-out like in ducks and some lizards or snakes. Either way, some shape-changing occurs. But not in alligators—when Kelly tried to artificially inflate the penis by pumping saline, it didn’t change in either length or diameter.

So, if the penis doesn’t inflate, how does the male alligator extrude it from the cloaca? Muscles would be the obvious answer, but continuing the theme of “really weird”, the penis has no muscles attached to it. It’s almost free-floating. One pair of muscles—the levator cloacae—cradle the penis like a sling, but doesn’t actually connect.

This stumped Kelly until she saw Moore’s video. She now thinks that when the levator cloacae contract, they force the penis out by squeezing the cloacal chamber. “This squishes the whole penis and pops it out of the vent,” she says. Indeed, when Kelly yanked on the levator cloacae by hand, the penis of her dead alligator leapt into the outside world.

I said the penis is almost free-floating. It’s got a tendon that connects to its middle, which helps to swivel it forwards when it pops out. Its base is also attached to the hip bone by a pair of large ligaments, that are “the consistency of the big rubber bands the post office uses,” says Kelly. When the penis comes out, these rubber bands are stretched. As soon as the levator cloacae relax, the elastic ligaments yank the penis back in.

Alligator penis. Credit: Diane Kelly

Alligator penis. Credit: Diane Kelly

This is just a hypothesis. Kelly now wants to do some tests of the muscles, tendons and ligaments to check that the “ones I think are everting the penis are actually the ones that are doing this”. Then, it’s time to look at living crocodilians to see how they actually use their penises, and how they might benefit from a permanently erect organ.

I leave you with this—an autographed cocktail napkin on which Kelly sketched out the alligators’ genital tract for me at a bar in Raleigh, North Carolina. She would like me to note that is it not to scale.

Cocktail napkin with schematic of alligator gentalia (NOT TO SCALE). Drawing by Diane Kelly; photo by Ed Yong

Cocktail napkin with schematic of alligator gentalia (NOT TO SCALE). Drawing by Diane Kelly; photo by Ed Yong

Reference: Kelly. 2013. Penile Anatomy and Hypotheses of Erectile Function in the American Alligator (Alligator mississippiensis): Muscular Eversion and Elastic Retraction. Anatomical Record http://dx.doi.org/10.1002/ar.22644

More on crocodilians:

 

There are 8 Comments. Add Yours.

  1. Noumenon72
    February 13, 2013

    I was kind of bummed that the link to “infamous duck penis video” doesn’t seem to contain a video. This is a cool article though.

    Fixed! – Ed

  2. Laurie Wiegler
    February 13, 2013

    Is there any correlation between this weird phenomenon and the alligator personality? Are other animals/reptiles who might exhibit such a, uh, trait and who are equally aggressive? Could the erection possibly make the alligator very uncomfortable, and how does this influence mating when the gators get together and sing for the ladies?

    • Laurie Wiegler
      February 13, 2013

      Is there any correlation between this weird phenomenon and the alligator personality? Are other animals/reptiles who might exhibit such a, uh, trait equally aggressive? Could the erection possibly make the alligator very uncomfortable, and how does this influence mating when the gators get together and sing for the ladies?

  3. Jeff Hertrick
    February 13, 2013

    The World’s Weirdest Penis? Might be the echidna: http://channel.nationalgeographic.com/wild/videos/worlds-weirdest-penis/

  4. Noumenon72
    February 14, 2013

    Okay, my mind is blown by that duck one.

    I like Diane Kelly’s bio, it’s just so science-y.

  5. Jo Brodie
    February 14, 2013

    I’m now wondering if alligators have featured much in local medicine anywhere, similar to the use of tiger penis in traditional Chinese medicine as a supposed cure for erectile dysfunction. Tigers perhaps easier to shoot though.

    I also have to admit that I initially misread “mississippiensis”.

    Jo

  6. Julie
    February 14, 2013

    Wired

  7. Richard M Jones
    March 3, 2013

    Mother Nature, for the careful observer, generally evolves using a “replicate and differentiate” strategy starting at the genetic level, as all things do start at the level.

    Mother Nature, also observed another rule, called if it “works don’t change it”, or the old saw, “if isn’t broke don’t fixit.”

    What we see here is doesn’t lack for variety, as much as it affirms sameness preserved for very long time.

    So which is it? The size of the wave, or the motion of the ocean?

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