Octopus has parasites?! Octopus: That's my partner's penis...

In 1829, Georges Cuvier, a leading figure in the field of zoology, found a "parasite" in the body of an octopus (an octopus) and gave it a scientific name. But the great man did not know that it was actually a reproductive organ.

Not a parasite?

In most male octopuses and squids, one or a pair of tentacles are specialized organs for sperm delivery, called hectocotylus (the name comes from the genus name given to it by Cuvier). During mating, the male argonaut's genitals will automatically break off and remain in the female argonaut's body.

Right: Female Argonaut, Top: Male Argonaut, with long stemmed arms extended | Dr Mary Gillham Archive Project / Flickr

After leaving the body, the stem arms still have a certain degree of mobility. Cephalopod sperm is packed in spermatophores, like a package of goods, so the stem arms separated from the body will not affect the transmission of sperm.

A relative of the Argonaut, Tremoctopus violaceus, has one of the largest sex differences in the world. The female is 50 times longer than the male, and weighs 10,000 times more. To help it “explore” its huge body, Tremoctopus violaceus’s stemmed arms are longer than its body. However, we still don’t understand the details of how the stemmed arms work.

The stem arms of the deep-sea octopus Bathypolypus arcticus | Picryl

By the way, the stalked arms are not penises. Cephalopods have penises, but in species with stalked arms, the penis is not responsible for the transfer of sperm. Chiroteuthis mega of the family Chiroteuidae does not have stalked arms, but its penis is very long and can be used to place spermatophores into the female body.

Sea slug martial arts

Sad fact: In the animal world, male genitalia loss is not uncommon but fairly common. Scientists even have different terms for it: in slugs, it's called apophallation, and in spiders, it's called emasculation.

The Call of Sorrow... | Golden Kamuy

The next question is, the purpose of evolutionary adaptation is to pass on more genes, so why do animals want to kill themselves? The answer is (again) the evil sperm competition: under some extreme conditions, sacrificing the penis can increase its own fertilization rate.

A study published in the Journal of Ethology by Ayano Sekizawa et al. listed eleven sea slugs that break off their penises. Ten of them break off during mating, and the tip of the penis remains in the reproductive tract of the other slug, acting as a plug to prevent other sea slugs from fertilizing again. Goniobranchus reticulatus breaks off its penis after mating, probably because its penis has a weird structure and is difficult to retrieve, and the reason for this weirdness is that it uses its penis to scrape out sperm left in the reproductive tract by other "people".

The brightly coloured sea slug G. reticulatus | Bernard Picton / Wikimedia Commons

Because sea slugs are hermaphrodites, the pain of losing a penis must be borne by both parties. Fortunately, the sea slug has a long "spare penis" in its vas deferens, which can be "pushed out" as a replacement after losing the penis, just like a mechanical pencil.

Slugs fall

Slugs and sea slugs are both gastropods, but they are not closely related. The genus Ariolimax is the largest land slug in North America. Some species are bright yellow, which has earned them the cute nickname "banana slugs." The male genitalia of banana slugs are so large that they occasionally (about 4%) fail to pull them out during mating, and the partner will bite them off.

The female reproductive tract of banana slugs is surrounded by muscles that can clamp the penis and prevent it from being pulled out. It seems that the sea slug loses its penis because the recipient of the penis "commits the crime", which is different from the "active cutting" of argonauts and sea slugs. Banana slugs can mate with multiple of their own kind, so there is a competitive relationship between "rivals" among slugs. At this time, the strategy that can increase the rate of fertilization of eggs is evolutionarily advantageous.

Mating banana slugs | Heike Reise & John MC Hutchinson / Trends in Ecology & Evolution (2002)

Banana slugs are unwilling to mate with their own kind that cannot provide sperm. If they lose their penis, they will "fail in love" and will no longer be able to accept sperm from their "rival", thus ensuring the fertilization rate of the first slug. After the slug bites off the penis, it can also take it out and eat it, which can be regarded as making the best use of it.

However, because slugs are hermaphrodites, when both parties are being penetrated, they are also being penetrated, so there is a possibility that both parties' penises will be bitten off. The result of involutionary competition is often that both sides suffer.

Spider

The male external genitalia of spiders are a pair of tentacle-like organs growing near their mouths, called pedipalps, which work like a syringe. The male spider discharges semen, which is sucked into the pedipalps and injected into the two genital openings of the female spider. Another function of the pedipalps is to automatically break off and block the genital opening, which is very similar to the penis of sea slugs, but the degree of involution of spiders is even higher, and there are even three "schools" of "brave men breaking penises".

During mating, the male Herennia multipuncta's pedipalps used for insertion will break off, blocking the female's genital opening. The "plug" is not completely sealed, and other males can still take advantage of the gap to get in, so the male spiders who have lost their pedipalps will still stay by the female spider's side and drive away their "rivals". Spiders that have lost their pedipalps are even more ferocious than intact male spiders. Is this considered a master of the palace?

Echinotheridion gibberosum, a member of the family Theridiidae, with the pedipalps (arrowheads) remaining inside the female after copulation | Matjaz Kuntner et al. / Biol. Rev. (2015)

Argiope aurantia is even more tragic. When the male spider mates for the first time, the organ used for insertion is broken off. After the second mating, he will die directly. Because the male spider is very small (only 1/50 of the female spider), he hangs on the female spider like a towel. After the female spider "takes him off", the pedipalps will be completely broken off, blocking the entrance of the female's spermatophore.

Tidarren sisyphoides of the family Theridiidae advocates the idea of ​​letting go. They are one of the spiders with the largest gender disparity. The weight of a female spider is 100 times that of a male spider. To match, the pedipalps are also quite large. The two pedipalps together account for 20% of the weight of a male spider. But the side effect is that the male spider cannot run fast with such a huge burden. Therefore, he will cut off one of his pedipalps and go out to find a mate with a light load. This is not enough. After mating, the male spider will die. He has lost the ability to fertilize. From the perspective of gene transmission, he is already a meaningless stepping stone.

After molting, E. gibberosum throws away one of its pedipalps (arrowed) to reduce the burden of walking | Matjaz Kuntner et al. / Biol. Rev. (2015)

References

[1] Reise, Heike, and John MC Hutchinson. "Penis-biting slugs: wild claims and confusions." Trends in Ecology & Evolution 17.4 (2002): 163.

[2] Miller, Brooke LW. Sexual conflict and partner manipulation in the banana slug, Ariolimax dolichophallus. University of California, Santa Cruz, 2007.

[3] Sekizawa, Ayami, et al. "Another usage of autotomized penis." Journal of Ethology 39.3 (2021): 319-328.

[4] Ramos, Margarita, Duncan J. Irschick, and Terry E. Christenson. "Overcoming an evolutionary conflict: removal of a reproductive organ greatly increases locomotor performance." Proceedings of the National Academy of Sciences 101.14 (2004): 4883-4887.

[5] Daphne Fairbairn, A Mismatched Pair: Gender Culture in the Animal Kingdom, translated by Li Fang. Shanghai: Shanghai Culture Publishing House, 2018.

Author: Little Wombat

Editor: pee pee shrimp

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