Male octopus poisons its mate to avoid becoming post-sex snack

While the bite from a venomous blue-lined octopus (Hapalochlaena fasciata) can result in a painful, potentially life-or-death emergency for humans, new research indicates it’s part of everyday courtship for the eight-limbed mollusks. And in the case of the male blue-lined octopus, his neurotoxin supply serves as a defensive mechanism against his mate.

Sexual cannibalism is documented across a wide range of species, particularly in many mantises and spiders. While unfortunate for the males, becoming a post-sex meal offers the females vital nutrients needed to sustain themselves and their soon-to-be hundreds of gestating offspring. This practice is especially common in animals exhibiting female sexual dimorphism, an evolutionary trait in which one sex is larger than the other.

Cannibalism among sexually dimorphic animals isn’t restricted solely to insects and arachnids. It also occurs with some crustaceans, gastropods, and even octopuses. And while a female blue-lined octopus is usually about double the size of a male, they are still prone to hunger pangs after mating. Unlike some species’ males who willingly allow themselves to be eaten, the male blue-lined octopus isn’t too thrilled by the prospect. According to recent evidence from researchers at the Queensland Brain Institute, their toxic saliva is often key to increasing the octopod’s odds of survival.

The new findings are documented in a study published on March 10 in the journal Current Biology. In laboratory observations, a team found that male blue-lined octopuses will bite their chosen mate near her aorta at the beginning of courtship. Within minutes, the neurotoxin known as tetrodotoxin (TTX) floods the female’s system as their breathing slows to a literal stop. During this hour-long asphyxia-like state, her skin turns pale, pupils construct, and she will become unresponsive to many external stimuli. The male, meanwhile, transfers his spermatophore (sperm packet) into the female. But instead of slowed breathing for him, his respiration actually increases from 20-25 to 35-45 breaths per minute. The female octopus eventually pushes away her mate shortly as the TTX effects subside, giving the male additional time to flee to a safe distance.

Although both sexes produce TTX for immobilizing prey and defending themselves, researchers noted the male blue-lined octopus salivary glands are as much as three times heavier than those found in females. But because killing the mother of their offspring defeats the whole purpose of reproduction, the team believes female blue-lined octopuses have likely evolved a higher tolerance to TTX, similar to their close relatives, the blue-ringed octopus.

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