Male blue-lined octopuses inject females with venom during sex, paralysing their larger mates to avoid being eaten, new research has found.
The blue-lined octopus is a tiny, highly dangerous cephalopod found commonly in shallow reefs and tide pools.
One of the four species of blue-ringed octopus, it uses an extremely potent neurotoxin called tetrodotoxin – also found in pufferfish – to immobilise its prey.
A new study suggests that male blue-lined octopuses use a precise bite to inject the venom into the female’s aorta at the beginning of mating.
Full-sized females are about the size of a golf ball – around two to five times bigger than their male counterparts – according to the study’s lead author, Dr Wen-Sung Chung of the University of Queensland.
Female octopuses are prone to eating their mates, he said.
“Sexual cannibalism is very common in cephalopods.
“When female blue-lined octopuses lay eggs, they spend roughly six weeks without feeding just looking after the eggs. They really need a lot of energy to get them through that brooding process.”
Male octopuses have a specialised arm for mating – known as the hectocotylus – which transfers a sperm capsule into the female’s oviduct.
Males have developed distinct strategies to avoid falling prey to their mates during copulation: the argonauts, for example, sacrifice their mating arm and let it drop off after mating. Other species have an elongated hectocotylus.
“The blue-lined octopus’s mating arm is much shorter,” Chung said. “Unable to do long-distance mating, they need to do a mounting mating strategy.”
The researchers observed male octopuses immobilising females during mating sessions that lasted between 40 and 75 minutes. As the tetrodotoxin took effect, the females stopped breathing after about eight minutes, turning pale and their pupils no longer responding to light.
“Mating ended when the females regained control of their arms and pushed the males off,” the scientists noted.
None of the females died during copulation, and they fed normally the following day, suggesting resistance to tetrodotoxin, Chung said.
Envenomation by blue-lined octopuses can be deadly to humans; fatal cases have also been documented in green sea turtles in Moreton Bay, who accidentally ingested the octopuses while eating seagrass.
Blue-lined octopuses, like most octopus species, exhibit semelparity, a breeding strategy in which an organism dies after it reproduces once. The males die soon after copulation, while the females die after their larvae hatch.
Chung called the unusual mating technique in blue-lined octopuses an evolutionary “arms race” between the two sexes.
“Because the females became much bigger and stronger … the male eventually needed to have a specific strategy to make sure his genes can be transferred to the next generation.”
The research was published in the journal Current Biology.
