A team of biologists from the University of Queensland (Australia) has discovered that male blue-ringed octopuses (Hapalochlaena fasciata) inject venom into females during mating to prevent being eaten. The blue-ringed octopus is one of four species in the genus Hapalochlaena, all of which are deadly to humans. The male octopus administers a dose of tetrodotoxin to immobilize the female during reproduction. The toxin doesn’t kill her; it paralyzes her temporarily. Other animals — flatworms, mollusks, amphibians, and fish — also use this lethal neurotoxin for defense, hunting, and to fend off aggressive mates.
Here’s what else the team found. The authors of the new study reported that female blue-ringed octopuses are twice the size of males. Despite this, the salivary glands of males are about three times heavier than those of females. During mating, males risk being eaten by their partners, as reported by the Independent. To protect themselves, males bite the females, rendering them immobile for the mating process, which typically lasts about an hour. In a laboratory experiment, the researchers found that males use a “precision bite” to inject tetrodotoxin into the female’s aorta during copulation. Within about eight minutes the female stops breathing, her body turns pale, and her pupils no longer respond to light — signs of paralysis.
“In this state — resembling asphyxiation — the female’s body color became paler. The pupils constricted and lost their reflex to bright flashes of light, a symptom of loss of nerve control seen in tetrodotoxin poisoning,” the researchers wrote. After mating, females regained limb control and pushed the males away, the researchers reported. The study added, “None of the female octopuses involved in the study died, indicating their resilience to the lethal toxin.” However, they did sustain injuries at the bite sites.
The study authors suggest this male strategy likely evolved to reduce the risk of cannibalism after mating. The team wrote, “Poisoning the females renders them immobile, allowing males to successfully mate.” The results of the study were published in the journal Current Biology.
