Friday Weird Science: Echidnas like it cold and torpid

Ok, I'll admit, this post is kind of stolen from the fabulous Ed Yong of Not Exactly Rocket Science, who just won the Association of British Science Writers' Best Newcomer award! Imitation is the most sincere form of flattery, Ed. :)

Well, the post isn't stolen, but the subject is. And it's actually been a little disappointing. When I first scanned the title, I thought it said "echinoderm", rather than "echidna", and I thought "Starfish sex!!! w00t1!!!" But no. Instead of talking about these getting it on:

(oh yeah)

We're talking about these:

(Via Ed)

You see? It's just...not the same...sigh...well, ok, they're pretty cute. Check out Ed's post for an adorable video.

Morrow and Nicol. "Cool sex? Hibernation and reproduction overlap in the echidna" PLoS ONE, 2009.

I'm sure you all know by now about the many types of animals that hibernate. Echnidnas (echidnae?) are one of them. Hibernation is more than just a nice snooze, the body temperature drops almost to that of the surrounding environment, and metabolism also drops accordingly. As you might imagine, this is not really conducive to a good sexual time. Especially not for males, who need to be energetic enough to find something and mount it, but also for females, who have slowed fetal development (if they're pregnant), and inhibited lactation.

But all this could change if competition for mates is really fierce. This can happen in two situations. 1) When there aren't enough females, and 2) when the females are promiscuous. Not enough females seems pretty obvious, but if females are promiscuous, mating competition will also increase. After all, then you not only have to find something and mate with it, you have to ensure that what you found isn't going to go off and mate with something else, displacing your sperm and maybe your babies in the process.

Echidnas are known both for being extremely promiscuous and for having "bouts" of hibernation, wherein they are sometimes more torpid than others. So in this study, the authors wanted to find out if the extreme promiscuity of the females led to the males taking to extreme measures and shorting themselves on sleep. They tagged and radio tracked (as well as video-taped) a whole bunch of echidnas. And the females they could catch, they swabbed to see if they had sperm in their vaginal tract, and if they could tell, who the sperm was from.

First off, they found that echidnas don't seem to suffer from as much delayed reproduction as other mammals. One of the echidnas they tracked had an egg in her uterus, though it's possible that she was delaying parturition until she woke up. And from patterns of breeding in other echidnas, it seems that this is pretty common. When a female wakes up from hibernation, she's often already pregnant.

So how does one get in this delicate condition while torpid? Well, the male takes advantage while you're sleeping. The scientists found numerous mating groups of echidnas, some of which had FOUR males to one poor, sleepy female. This seems like a bit much, but when echidnas are fully awake, they can form "mating trains" of up to 11 males and females, all gettin' it on ("come on ride the train...and ride it.."). So four isn't that excessive. Interestingly, while the males were all at normal body temperature and activity, the female often wasn't, and sometimes, though not completely torpid, wasn't what you would call awake.

So how does it happen that the males are all active while the females are sleeping? The hibernation cycles of male and female echidnas actually do not overlap. While male echidnas sleep from May to August, females snooze from June to September. This means that the males wake up and have a full month to find some females and get a round in before she wakes up. As the gestation period for the echidna is only 22-24 days, she has time to get pregnant, and then when she wakes up, she can have the egg almost immediately. Since echidnas only have one egg per mating, this could be pretty useful in keeping the population up.

So how did the males figure this bit out? When there's a lot of competition for mates, nature favors males who are sly, or have traits that increase their competitiveness. This could include anything from, say, having sperm that dissolves or blocks other sperm, to simply switching your sleep schedule a little, giving you an extra window of time. Then the male echidna can latch on to a female, mate with her, and guard her while she's asleep, so she will bear his egg when she gets up. This is smarter than it sounds, as I imagine a fully awake lady echidna is a lot harder to guard than a hibernating one.

On the other hand, this also has to select for a subset of male echidnas that find the relative coldness and total torpor of the lady very fascinating. While she wakes up a little, she often goes back into hibernation immediately afterward, and her body temperature will probably not get back up to normal. Oh yeah, look at that cute lady echidna, so cold, so slow moving...

Morrow, G., & Nicol, S. (2009). Cool Sex? Hibernation and Reproduction Overlap in the Echidna PLoS ONE, 4 (6) DOI: 10.1371/journal.pone.0006070