Today we have three videos about spiny things, but only one is related to kittehs. First, if you have a male cat, you may have noticed that his penis has spines on it (these seem to disappear after castration). As this National Geographic video shows, the spines are essential for successful mating. (Although the video suggests that the female’s postcopulatory rolling may help sperm get to the eggs, I’m not convinced.)
Here’s the penis of a male cat, showing the spines:
Although the spiny anteater, or echidna, eats ants, it isn’t really an anteater in the classical sense (those tube-nosed South American mammals of the order Pilosa). It is, instead, a monotreme: one of the two primitive mammals that, along with the platypus, lays eggs. And males have a bizarre generative organ, a penis with four heads. It looks for all the world like the creature from Alien bursting from the groin:
The function of the echidna’s clumped sperm that swim as a unit is unclear, but recent work suggests that, in species where females mate multiply, it’s an adaptation for a male’s sperm to win the race to the egg. By joining with another sperm from the same ejaculate, your swimming speed increases, upping your chance of being the first to fertilize. Clearly, two tails are better than one. (Note that this behavior is facilitated if the sperm are related. Because only one sperm can fertilize an egg, if two join together and penetrate the egg, only one of them will pass on its genes. But if you’re related to other sperm, a form of kin selection can promote the evolution of clumping.)
It’s been shown in deer mice (whose females mate multiply) that when you mix sperm from ejaculates of different males, the sperm that clump together tend to be those from the same male. There may be some “recognition molecule” on the sperm’s surface that helps it discriminate between “brother” sperm and unrelated sperm. In contrast, when sperm from males of a monogamous mouse species are mixed together, there is no tendency for related sperm to clump. Presumably this is because in those species the ejaculates of different males never co-occur in a wild female.
Finally, just for lolz, here’s a hedgehog in the bath. Be sure to watch until he inverts. (Warning: baby talk!)