When I first heard about giant sperm, I thought those MUST be the greatest. I mean, why have a giant copulatory organ when you can let the sperm speak for itself? Some species of ostracods (a type of crustacean) can have long sperm that are TEN TIMES the body length of the ENTIRE ANIMAL. I mean, it's sooooo big.
So why would it be hard to have big sperm? Well...you have to get them out there SOMEHOW. And when your sperm is bigger than you are, that's got to be a difficult proposition.
And in the super tiny ostracod Pseudocandona marchica, it means having a special organ, a strong, filamentous, muscular tube, that resembles nothing so much to me as...a sperm cannon.
Yamada and Matzke-Karasz. "How is a giant sperm ejaculated? Anatomy and function of the sperm pump, or “Zenker organ,” in Pseudocandona marchica (Crustacea, Ostracoda, Candonidae)"
(That's not the sperm, it's not the cannon. It's the whole animal. Source)
NOTE: Today's post comes to you from Improbable Research, where they did a profile of this paper. And me? I'm a sucker for a giant sperm.
There are so many things I love about this study. Giant sperm. Sperm cannons. Beautiful pictures of sperm cannons. And the best part? All specimens for this study were collected from a flooded flower pot on the campus where the scientists worked.
A flower pot.
Man I wish I could get specimens like that. My jealousy has no bounds.
So, Pseudocandona marchica is a VERY small microscopic organism that...lives in flower pots, apparently. And it has giant sperm, long filamentous cells much longer than the P. marchica (can I call you P. chica?) itself. Giant sperm that it has to get OUT of its tiny little body somehow.
But how? Well, studies of the organism had long noticed a particular body part on this creature. You see that spirally thing up there in the photo? The bit that's circled? That is Zenker's Organ (so called after the dude who named it. Again, I'm jealous. If anyone ever wants to name an organism's copulatory machinery after me, I would be nothing short of honored. Biologists, take note). They knew it had something to do with reproduction (the first person, in a burst of awesome, called it “Ejakulationsapparat”), but no one was quite sure how it worked. It appeared to be an ejaculatory apparatus, but no one knew quite how.
But the authors of this paper took one look at that spirally organ and knew they had to figure it out. They gathered their P. chicas, and did some really lovely scanning and transmission electron microscopy. The pictures they got are wonderfully detailed and really very artsy (I would have all of these as art!)...and also pretty dirty when you realize what you're looking at.
What we have here is the tube itself, made of chitin, a strong filamentous material. This tube is in turn surrounded by smooth muscle going the length of the tube. And at one end, there is a "cogwheel" type shape, which in non-mating animals is closed.
So it's a pretty nice basic structure, with six repeating segments.
But how does it work?
But of course, where are the giant sperm during all this? The authors observed that there were no sperm in the tube in non-copulating males, but in a mating pair of the animals, they found a HOLE. A hole at the end of the tube, a hole in the cogwheel! That had been opened during copulation.
But what caused the opening? After all, the smooth muscle runs up and down the length, there's NO muscle in the cogwheel shape at the tip...and the cogwheel itself is closed. So how does the cogwheel shape open? The authors performed various models, and concluded that it's not muscle that opens the tip of the tube. It's pressure. The pressure from the giant sperm opens the tip of the cogwheel, allowing one sperm through at a time to head over toward the chosen lady. Once the one sperm is through, the smooth muscle along the sides of the tubes contracts to help propel it out into the world. Like a very slow cannon. Which is why I'm calling it the sperm cannon, though it's technically the "ejaculatory apparatus".
And this is pretty different. Most animals like this have smooth muscle around the base of the ejaculatory organ, where the cogwheel is, which can contract to open the duct. But not P. chica. It needed another method. A pressure method. And with this method the giant sperm can move, one at a time in what I would like to think is a stately procession, down the tube and out toward the female, propelled by pressure and by smooth muscle contractions.
So HOW do you ejaculate a giant sperm? Slowly, man, slowly.
Yamada S, & Matzke-Karasz R (2012). How is a giant sperm ejaculated? Anatomy and function of the sperm pump, or "Zenker organ," in Pseudocandona marchica (Crustacea, Ostracoda, Candonidae). Die Naturwissenschaften, 99 (7), 523-35 PMID: 22684272