Friday Weird Science: Slutty Sloppy Barnacle Spermcasting

Jan 18 2013 Published by under Friday Weird Science

Ah, barnacles. You wouldn't really think that something with the reputation of...well, of being a barnacle, would really have an exciting sex life. I mean, they're barnacles. They are the very definition of something that is stuck in the mud. They hatch, they head to the open ocean for a few glorious weeks as whale-food, and if they survive the experience, they find a nice rock (or pier, or the bottom of a boat, or possible a whale if it wants to see the world) to call home. And never move again. Thus, the reputation of the barnacle is sealed as being possibly the most boring of creatures.

But it's not true. You see, when you're stuck to a rock, well, it's hard to meet people. If you know what I mean. You don't get out much. And so when it comes to passing on the species, barnacles have had to get creative.

The first thing that this results in is the biggest penis (relative to body size) in the world. It can be up to eight TIMES as long as the animal itself. When you're stuck to a rock, and you feel the need to breed, sometimes you have to let your penis do the walking.

barnacle penis
(Heeeeeey, ladieeeees. Source)

And of course, you have to watch these things in action.


(Source. Did you see the one in the back just whip it out?! Barnacle porn, my friends)

You can see above how the barnacle gets it on. The penis basically hunts blind until it hits another barnacle. Then it deposits sperm into the mantle of the barnacle, which can then be used to fertilize eggs.

The longest penis in the world works well if your lover is just the next barnacle over. But what if you're all alone? What do you do?

Well, barnacles are hermaphrodites, and for many years (since Darwin, in fact) it's been thought that if they can't find someone to do for them, they just do for themselves. Self-fertilize, etc. People have often found lone barnacles with fertilized eggs, so they just assumed it happened. But while there's great video of barnacle mating, there isn't any of self-fertilization. Are barnacles just shy masturbators?

Nope, it's more than that.

Barazandeh et al. "Something Darwin didn't know about barnacles: spermcast mating in a common stalked species" Proceedings of the Royal Society B, 2013.

So, barnacles in general have long penises. But some barnacles are more well-endowed than others. Observe, for example, the Pacific gooseneck barnacle (Pollicipes polymerus).

barnacle penis3
(Source)

Though really very pretty, this barnacle is not exactly packin', at least, not by barnacle terms. Considering that some species of barnacle have penises 8 times their body length, this one is really not that much longer than the barnacle itself (though longer when it gets exicted).

barnacle penis2

See the arrow up there? That's pointing to the penis. I think we're all pretty unimpressed.

So really, this barnacle is limited to more immediate neighbors. So how well does mating happen? And the solitary barnacles that don't have neighbors, how are they supposed to get by?

Well, the authors of this paper noticed something. They noticed that the barnacles they were observing were releasing something during low tide. Something that looked a lot like sperm.

bernacle penis4
(Look carefully. Notice the foamy stuff. Yeah)

What was the purpose of that sperm? Were the barnacles blowing off some extra steam? Or does that sperm release have a purpose?

The authors collected a bunch of isolated barnacles, ones not growing around others and so not within "penis length". Many of these had fertilized egg masses. They took the masses and did, basically, barnacle paternity testing. You can look for sets of single nucleotide polymorphisms (where one base in the DNA is a little different), and compare to various fathers to find out who's most likely. If the barnacles were self-fertilizing, the eggs would all be the same and so would the DNA.

But if the DNA was different...

...and so it was. The barnacles were definitely getting their sperm from somewhere. It turns out that the sperm released by barnacles at low tide was just...floating around in the water until a lonely barnacle could pick it up. This is a technique that's often used by sponges, and is called "spermcasting", when you release a ton of sperm into the water (don't drink the water), and hope it finds the right egg. But no one ever thought that barnacles did that before. Now we know.

So these barnacles...well they'll pick up anything! Any sperm! They aren't picky! It's just floating around in the water and they go ahead and snatch it up, like the sex version of the 5-second rule. It's still good!

Also, this just reinforces my feeling that ocean water is...just don't swallow. There's barnacle sperm in there. Unless, of course, you're into that.

Barazandeh, M., Davis, C., Neufeld, C., Coltman, D., & Palmer, A. (2013). Something Darwin didn't know about barnacles: spermcast mating in a common stalked species Proceedings of the Royal Society B: Biological Sciences, 280 (1754), 20122919-20122919 DOI: 10.1098/rspb.2012.2919

*One of the things I most value in papers is when the authors themselves know they are writing something FANTASTIC. These authors...they know it's funny. They like that it's funny. And I love them for it.

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