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Scientists don’t know much about how tardigrades have sex.
That’s a shame. Tardigrades — microscopic animals that primarily live in water — are some of the most fascinating creatures on Earth, with biological powers of resilience usually found in comic books.
They’re able to survive in just about any environment. They can withstand the shock of boiling water and temperatures that near absolute zero. They can survive in the crushing pressures of the deep ocean or go without water for decades. They’ve even survived in the vacuum of space. In 2014, Japanese researchers thawed a group of tardigrades that had been frozen for 30 years. It took just a few weeks for them to fully reanimate. And then they quickly reproduced.
If we know all that about tardigrades, we ought to know how they mate, right? Right?
“Although tardigrades have been studied for almost 245 years and by now more than 1200 species have been described, there are only a few publications concerning the life-history or mating behavior of tardigrades,” researchers at Germany’s Museum of Natural History Görlitz explain in the Journal of Zoological Systems and Evolutionary Research.
So the researchers set out to correct the gap in the science, filming 30 tardigrade couples copulating for a first-of-its-kind study.
First the scientists separated out males from females (a painstaking task because there are few clues as to a tardigrade’s sex). Once the males and females were separated, it wasn’t hard to pair them off to mate. The study authors write:
When put together with gravid [egg-carrying] females, males seemed to be attracted, moving directly towards the female and joining her for mating. On rare occasions males were not attracted to females, and this presumably occurred when females had started to absorb eggs.
The result: For the first time published in a scientific journal, here’s a video of two tardigrades getting it on.
Yeah, it’s a little hard to see what’s happening. Luckily, the scientists drew a cartoon diagram to help. Basically, the male (at the bottom of the diagram and on the right-hand side of the GIF) curls up around the female’s head and holds himself there with his front legs. The female then stimulates the male “by moving her stylets [mouth-like openings] and contracting the sucking pharynx [the throat],” according to the study authors.
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Put another way: The male tardigrade puts the female in a cuddly headlock, and then the female coughs a little bit to start the show.
The male’s semen then enters the female’s body, where it finds the eggs (pictured in the diagram as the three oval shapes on the female’s back).
The scientists note the whole process takes about an hour, during which “semen [is] ejaculated several times.” Now we can add marathon copulation to the list of this animal’s impressive abilities.
Further reading:
- This is how tardigrades achieve their remarkable resilience: When faced with harsh conditions, they can curl up and turn into “tuns,” expelling all water and bringing their metabolic processes to a screeching halt. It’s basically suspended animation.
- Watch tardigrades wake up after 30 years of hibernation and act like nothing happened.
