Friday Weird Science: Millipedes "talking" dirty

Feb 17 2012 Published by under Friday Weird Science, Uncategorized

This paper is one of those papers that gives official science manuscript writing a bad name. It's not that the paper is badly written, nor is it that the science is bad (in fact it's pretty cool). No, it's the JARGON.

"...posterior surface of the posterior telopod, which is actively moved over a field of sclerotized nubs on the inner margin of..."

"seems to prevent the female from volvating..."

"...and seems to be species-specific, arguing for a species recognition function of the stridulation during courtship..."

You know what this all translates as? Millipedes. Making sexy noises for the ladies.

With their BUTTS.

But I guess reviewers wouldn't be thrilled at that kind of description.

This is the creepiest thing I've seen today.


(Source)

But they DID go most of the way with the title.

Wesener et al. "How to uncoil your partner—“mating songs” in giant pill-millipedes (Diplopoda: Sphaerotheriida)" Neturwissenschaften, 2011.

The story behind this study is actually very sweet. Dr. U. Haacker was an entomologist in Germany who apparently did a lot of work on millipedes and their sounds. Unfortunately, when Dr. Haacker died in 1972, much of his work remained unpublished, the data unanalyzed. The authors of this study obtained his original recordings, specimens, and notes, and set out to complete his work. And here it is, in 2011 and in English, to bring his work to the largest possible audience. Science lives on.

The authors of this study were looking into the sounds of the millipede. Specifically, they are looking at Sphaerotherium a genus of millipedes belonging to the pillbugs (the giant pill millipedes, to be exact). They are native to South Africa. And they are BIG. When rolled up, they are the size of a golf ball.


(Source)

You might look at a millipede and think...well those things can't produce sounds! But they can, they just don't produce them with their mouths. Instead, they rub bits of themselves together to create sounds...and most importantly, to make vibrations. Because not only can these pillbugs not make SOUNDS, they can't HEAR either (or at least, they have no auditory parts as we recognize them).

And what are these vibrations for? Well, obviously, they are for the ladies. The idea is this:

1. Male giant pillbug comes across a likely other giant pillbug.

2. The male begins to try and angle his butt over near the potential partner. Right now, it cannot distinguish between a male and a female. So it's just guessing.

3. If the other giant pillbug feels the touch of the first, it might roll up immediately into a defensive ball. These guys aren't poisonous, so rolling up into a ball is about all they've got in the way of defense. To keep this from happening (if the target pillbug in question is a female, anyway), the male starts "stridulating", making noise. He does this by rubbing body parts together. Specifically, he rubs the body parts together near his anus. He rubs together two sclerotized (that's "hardened") sections of his body, two joints in his telopods, which are modified appendages in the back of the male, near the anus. These are used in sexual reproduction (hey, male reproductive parts are at there best when sclerotized), and it looks like they could also be used for making vibrations. By rubbing these hard bits together, these pillbugs can make quite a noise (you can hear it over at Wired, which covered this paper a while back).


(These are the millipede parts near the anus. You're looking at an electron microscope portrait of a pillbug's butt)

4. The male continues his stridulations. The female (we're assuming it's a female at this point), may try to crawl away, in which case he'll crawl after, and keep trying. Science fails to note whether the stridulations take on the desperate tone of "no baby! Don't leave!".

5. If the female stays put, the male crawls up and latches on, using his telopods (the body parts mentioned above) to grab her front legs. He then wriggles and stretches up so his head is near her anus and his anus is near her head (yes, this means millipedes ALWAYS 69).

6. After a suitable interval (1-2 minutes), the male ejects sperm near his HEAD (at the second leg pair), and transports the sperm with his legs down his body, depositing it near HER second leg pair, where her reproductive opening is located.

7. The male releases the female. Some short stridulations keep going in some species, probably along the lines of "That was great baby, I'll call you!"

The whole thing looks like this:

(This is a figure in the paper. I love this paper, despite the jargon)

So what is the purpose of all those stridulations, those loud noises? The authors hypothesize that it has to do with species identification. The patterns of stridulations varied according to species, most particularly in the timing and pattern. This makes sense for things like sensing vibrations, as there's no proof that these pillbugs can hear. And this is important for mating. The female wants to know that she's going todo her thing with the right species, and it's possible that, if confronted by the wrong pattern of stridulations, she'll roll up into her little hermetically sealed ball and he'll never get a date.

Unfortunately, right now a lot of this is a hypothesis, there are no direct experiments showing that females will uncoil in response to the right stridulations. But it seems pretty reasonable. After all, with those kind of sexy sounds, who wouldn't relax a little?

Wesener, T., Köhler, J., Fuchs, S., & Spiegel, D. (2011). How to uncoil your partner—“mating songs” in giant pill-millipedes (Diplopoda: Sphaerotheriida) Naturwissenschaften, 98 (11), 967-975 DOI: 10.1007/s00114-011-0850-8

Acknowledgements: Special thanks to @TGIQ, "The Geek in Question", who was kind enough to answer all of my questions on millipede anatomy!! And check out TGIQ's blog, it's good some cool entomology!

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