Revealed: the toxic sex life of the blue-lined octopus
Both male and female blue-lined octopuses produce a powerful neurotoxin called tetrodotoxin (TTX), used for hunting prey and as a defence against predators.
Now, scientists from The University of Queensland (UQ) have discovered that males also use TTX to immobilise females while mating, reducing the chance of being eaten afterwards.
It may explain why the venom gland in the male blue-lined octopus is about three times the size of the female’s.
As one of several blue-ringed octopus species endemic to Australia’s east coast, the blue-lined octopus (Hapalochlaena fasciata) is one of the deadliest marine creatures, its venom capable of killing people.
Hungry females
Female blue-lined octopuses are significantly larger than their male counterparts, posing a challenge for males.
“The female body size is usually about twice [the male’s] body weight. Some get up to five times bigger. So that’s a dramatic difference between the sexes,” explained Dr Wen-Sung Chung, a neuroscientist from UQ’s School of the Environment who is lead author on a report about the discovery in the latest issue of the journal Current Biology. “Because the male is so small, it [could] very likely be eaten by the female.”
But to boost his chance of reproductive success he deploys his venom during mating to reduce the likelihood of becoming a victim of sexual cannibalism.
Octopuses are semelparous animals, meaning females only breed once but prior to that both sexes are promiscuous.
“Sexual cannibalism is common in the animal kingdom,” Dr Chung said.
“The blue-lined octopus has used a very different strategy to try to avoid [being eaten]. I guess that’s the reason why evolution made the small male octopus be able to copulate with the much larger female.”
The female, meanwhile, has a vested interest in eating the male; she needs to hoard calories before her weeks-long fast while guarding her clutch of eggs.
“[After breeding] the female blue-lined octopus looks after her eggs for roughly six weeks, without feeding,” Dr Chung said.
Different species of octopus have evolved different strategies for males to avoid being eaten by females.
Some have a disproportionately long hectocotylus – the ‘mating arm’ that holds and transfers spermatophores (a package of sperms) to a female – allowing males to keep their distance from females during mating.
The male dwarfed Argonauta (also known paper nautilus) shed or discard their mating arms after copulation, allowing a quick getaway for males.
Toxic masculinity
During copulation, a male blue-lined octopus latches onto a female from behind and bites into her aorta, injecting her with TTX venom.
“After roughly 8-10 minutes the female [stops] breathing,” Dr Chung said.
“This neurotoxin basically makes the female lose all her muscle control. It’s very dramatic.”
The female then enters an asphyxia-like state; her pupils shrink, and her skin turns pale, losing its colouration.
Copulation typically lasts an hour, until the female regains her muscle control and shoves the male off.
Not all males were successful in their mating efforts. More than one met a gruesome end when eaten by the female.
