The venom of the male blue-lined octopus is made for its predators, its prey, and, apparently, its mating partners. That’s what researchers from the University of Queensland in Australia found after observing the males of the species sedating the females with venom prior to mating.
“Injecting the females renders them immobile,” the researchers wrote in a March Current Biology report, “allowing the males to mate successfully.”
Read More: The Tiny Blue-Ringed Octopus Is Iridescent and Deadly
An After-Mating Meal
All octopuses are venomous, with the majority of these cephalopods using their venom to fend off their predators or to immobilize their prey. Among the Hapalochlaena, or the blue-ringed octopuses, venom is often used in this way, being wielded by several species to fight threats and find food.
But the venom of the blue-lined octopus (Hapalochlaena fasciata) is also used for another application. Capturing 12 blue-lined octopuses — six male and six female — and monitoring them in captivity as they mated, the University of Queensland researchers revealed that the species’ venom is involved in mating, allowing the male octopuses to avoid sexual cannibalism.
Many female octopuses are bigger than male octopuses from the same species, meaning that it isn’t difficult for a female to consume a male once copulation is complete. As such, sexual cannibalism is relatively common among the cephalopods, being used by female octopuses as a way to fuel up for the demanding task of laying and looking after their eggs (a period in which they find little time to feed).
Female blue-lined octopuses are particularly prone to this behavior, thanks, in part, to their size. “Female blue-lined octopuses are about twice the size of males,” the researchers wrote in their report, “which bears the risk of males being cannibalized during reproduction.”
The team’s research reveals that the males aren’t always fated to become food, however. By biting and injecting their partners with venom before mating begins, they can safely copulate with females without becoming a meal after mating.
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Partner Paralysis
Piercing their partners’ aortas with their beaks, the male octopuses injected a dose of venom into the female octopuses’ bloodstreams. Though the venom, tetrodotoxin, paralyzes prey until they are consumed, it only paralyzed the females for about an hour — allowing the males to mount their partners and to transfer their sperm to their mates through their specialized mating arms.
According to the researchers, this strategy allowed the male octopuses to mate with the females without being cannibalized. Among the bitten females, paralysis was accompanied by slowed breathing, as well as an inability to respond to stimuli.
To successfully paralyze their partners, the males needed to access a substantial amount of venom. Luckily for them (though perhaps unluckily for their partners), the males’ salivary glands stored more venom than the females’ salivary glands, being about three times heavier.
Other male octopuses combat sexual cannibalism in other ways, by developing detachable mating arms, for instance. But none of these octopuses use toxins that are as potentially deadly as those of the blue-lined octopus, whose tetrodotoxin is dangerous to people as well as to prey and other organisms, like sea turtles.
While both male and female blue-lined octopuses are destined to die soon after mating (with the females living only long enough for their young to emerge from their eggs), the researchers found that this strategy allows males to escape from mating unscathed. Once the venom wore off, the females merely forced the males away, with all six females surviving to lay their eggs.
Read More: Octopuses Partner with Fish to Hunt, and Will Slap the Fish That Slacks Off
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
Current Biology. Blue-Lined Octopus Hapalochlaena fasciata Males Envenomate Females to Facilitate Copulation
Journal of Molecular Evolution. Tentacles of Venom: Toxic Protein Convergence in the Kingdom Animalia
Journal of Molluscan Studies. Levels and Distribution of Tetrodotoxin in the Blue-Lined Octopus Hapalochlaena fasciata in Japan, With Special Reference to Within-Body Allocation
Marine Biology. Death in the Octopus’ Garden: Fatal Blue-Lined Octopus Envenomations of Adult Green Sea Turtles
Sam Walters is a journalist covering archaeology, paleontology, ecology, and evolution for Discover, along with an assortment of other topics. Before joining the Discover team as an assistant editor in 2022, Sam studied journalism at Northwestern University in Evanston, Illinois.
