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Scientists have found that male blue-lined octopuses inject venom and paralyse females during sex to avoid being killed and cannibalised by their much larger partners.
The male octopus of this species precisely injects a dose of its deadly tetrodotoxin venom into the females to immobilise them during copulation, say researchers at the University of Queensland.
Several creatures, including flatworms, mollusks, amphibians, and fish such as the pufferfish use the deadly neurotoxin for killing prey and for self-defence.
The new study, published in the journal Current Biology, found that male blue-lined octopuses precisely target and bite the female’s main artery to make them immobile to avoid being cannibalised post reproduction.
The species, closely related to the blue-ringed octopus, uses symbiotic bacteria to sequester the tetrodotoxin venom in its salivary glands.
Scientists have previously documented the octopus using its toxin-laden saliva to paralyse large prey before it proceeds to devour them.
There have also been instances recorded in the past of the highly potent toxin causing lethal envenomation in humans.
While female blue-lined octopuses are about twice the size of males, scientists observed in the new study that the salivary gland in the males is about three times heavier than that of females.
Researchers have also known that males bear the risk of being cannibalised during reproduction.
By conducting octopus mating experiments in the lab, scientists found that the males use a “high-precision bite” to target the female’s aorta and inject tetrodoxin during copulation, which tends to last about an hour.
The toxin causes the female octopuses to stop breathing after about 8 minutes, turning their bodies pale, and their pupils to become unresponsive to light – signs indicating they’re paralysed.
“In this asphyxia-like state, the female body colour turned pale. The pupils also constricted, losing all reflexes to bright light flashes, symptomatic of a loss of nerve control such as during tetrodotoxin envenomation,” scientists wrote.
“Once the females were immobilised, the males successfully copulated and mating ended when the females regained control of their arms and pushed the males off,” they wrote.
None of the female octopuses in the study died, suggesting they are resistant to the deadly venom.
They did however show signs of injury, including humps and open wounds at the site of bite.
This strategy by the males to paralyse their partners likely evolved to mitigate the dangers of being cannibalised post copulation, scientists say.
“Envenomating the females renders them immobile, enabling the males to mate successfully,” they wrote.
Source: independent.co.uk
