Caturday felid: spines!

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!)

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10 thoughts on “Caturday felid: spines!

  1. LOL, unexpected! Fortunately something of teh cute too.

    Clearly, two tails are better than one.

    Not so clearly to me – roughly same mass-to-force relationship, how the tails interact can go either way, and if it’s a shorter race the backup/rest opportunity from a “twin engine” isn’t all that it is said to be.

    But clumping should diminish the effective viscosity-to-force ratio. Slick swimmers FTW!?

    1. At low values of the Reynolds number, friction is proportional to the diameter. So a clump of four cells has four times the power, but only twice the drag force.

    1. I’m not sure what you are saying. That foreskin is hindsight (selected) or purely accidental?

      Foreskin is claimed to have at least two functions – it or its neighboring tissue is connected to the immune system, and it makes mechanics of sex different and claimed to be more gratifying for the female. Both would be selected for, right?

      1. Um, and of course they could both be connected, as prolonged time before ejaculation (one of the gratifying effects, I take it) would mean more immune system exposure. Or is it only females that are thought to adjust the later to promote fertility?

      2. And more gratifying for the male.

        Isn’t it anthropomorphic to describe the female’s sensation as “pain”?

        Wouldn’t flat blades be more efficient at scraping out predecessors’ sperm?

        Those spines seem homologous to the spines on the tongue. Their layout is similar.

        Are they also homologous to the “pearly penile papules” of the human corona glandis?

  2. Good stuff as always.

    Caught one typo: “those tube-nosed South American mammals of the genus Pilosa”

    Pilosa is an “order” of xenarthran placentals that also includes the sloths. To get to exclusively anteaters, we need to get down to the “suborder” Vermilingua (a good example of colorful taxonomy).

    1. Oh dear. Yes, I meant “order.” At least I didn’t say “Edentata,” which is now obsolete. I’ve corrected it, thanks.

      1. At least I didn’t say “Edentata,” which is now obsolete.

        Crap. So am I, apparently.

        (Interestingly [and once more belatedly] I was just reading about how the acoel flatworms are no longer platyhelminths…)

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