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. According to the researchers, the male octopus administers a dose of tetrodotoxin to immobilize the female during reproduction. This toxin does not kill the female; it merely paralyzes her for a short time. The scientists also noted that other members of the animal kingdom, such as flatworms, mollusks, amphibians, and fish, can use this lethal neurotoxin to protect themselves from aggressive sexual partners, as well as for hunting and self-defense.
What else did the scientists learn? 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. Under the influence of the toxin, the female stops breathing in about eight minutes, her body turns pale, and her pupils cease to respond to light. These are signs that the partner is paralyzed.
“In this state, resembling asphyxiation, the female’s body color became paler. The pupils constricted, losing their reflexes to bright flashes of light, which is a symptom of loss of nerve control, such as in tetrodotoxin poisoning,” the scientists shared in their observations. After mating, the females regained control of their limbs and pushed the males away, the researchers reported. They also noted, “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 scientists explained that this strategy of males to paralyze their partners likely evolved to reduce the risk of cannibalism after mating. Thus, “poisoning the females renders them immobile, allowing males to successfully mate.” The results of the study were published in the journal Current Biology.