Deadly secrets uncovered

Scientists have laid bare some of the poisonous secrets of the spectacular blue-ringed octopus.

James Cook University PhD student Brooke Whitelaw led the study. She said the animal is unique, renowned for their striking iridescent blue rings, which are flashed to advertise a potent neurotoxin located in their venom and tissues.

“In order to understand the evolution of this unique genus we sequenced and examined the genome of the southern blue-ringed octopus. They are the only octopods known to store large quantities of the potent neurotoxin, tetrodotoxin, within their tissues and venom gland,” said Ms Whitelaw.

Tetrodotoxin is more toxic than cyanide and causes muscle paralysis which stops the octopus’ prey from breathing. It is also effective against potential predators, including humans.

“We found that the southern blue-ring octopus displays a different venom composition to other octopods, which do not possess tetrodotoxin.

“Most other octopods carry an array of venoms within them. We found differences in the blue-ringed octopus’ genes that suggest the quantity of tetrodotoxin within its venom may be so potent that many toxins necessary to other octopods are not required by the blue-ringed octopus to hunt and protect itself,” said Ms Whitelaw.

She said the origin of tetrodotoxin in the blue-ringed octopus is still under investigation, however some bacterial species are known to produce tetrodotoxin in the marine environment.

“Our results show a diverse array of bacterial species in the venom gland, some of which may be potential sources of tetrodotoxin. Identifying, which species are capable of producing tetrodotoxin and the possible relationship between the octopus and its bacteria will be a complicated job for the future,” said Ms Whitelaw.

She emphasised how little is currently known about the genomic evolution of octopuses and other cephalopods (octopus, cuttlefish and squid). As the first cephalopod genome (Californian two-spot octopus) was only published in 2015.

“Our analysis provides the first glimpse into changes underlying the genome evolution of the southern blue-ringed octopus relative to closely related octopod species. Overall, it’s a substantial contribution to understanding the evolution of this genus.”

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