Octopuses can taste with their arms, and a new study reveals that specifically, they’re tasting chemical cues from microbes that grow on the surface of objects like dead crabs and living octopus eggs. These ‘flavors’, it turns out, can signal which prey is worth pursuing, or which egg isn’t going to make it.
Octopus arms bristle with neurons that inform these fascinating animals’ behaviors, sometimes even independently of their brains. Sensory receptors in their arms enable them to ‘taste by touch’, which is essential to how they decide what to nurture, what to hunt, and what isn’t worth their time.
That’s important information for these opportunistic hunters, who forage mainly at night and in shadowy crevices.
“If a microbial strain could activate a receptor, then it could generate a neural signal that tells the octopus: This is something I care about,” says Harvard University biochemist Rebecka Sepela, who led the research.
Related: Male Octopuses Stun Females With Venom to Survive Mating, Study Finds
“The microbiome is acting almost like a chemical translator. It integrates environmental signals – like changes in temperature or nutrient levels – and outputs molecules that inform the octopus how to behave.”
Proving this to be the case was an ambitious mission. The team isolated 295 different strains of bacteria from ‘biologically meaningful’ surfaces in the natural environments of wild-caught California two-spot octopuses (Octopus bimaculoides). Those meaningful surfaces included food and family: the shells of fiddler crabs (Leptuca pugilator), and egg casings of the octopus’s own offspring.
“Those microbes produce molecules that allow the octopus to tell the difference,” Sepela says. “Microbes are chemical factories. They constantly take in environmental cues and produce molecules that reflect their surroundings.”
The shells of living crabs, for instance, are surprisingly sterile, while those of decaying crabs are quickly colonized by a dense tapestry of bacteria.
Octopus egg casings tended to by a mother octopus have a curated balance of microbes, but when discarded, this is thrown off by an overgrowth of spiral-shaped bacteria.
The screening – in which Sepela’s team painstakingly tested how octopus sensory receptors reacted to each of the nearly 300 strains – revealed that just a few of these microbes, found on decaying prey or unhealthy eggs, activated the octopuses’ receptors.
To test these signals in action, octopuses who were actively brooding a clutch of eggs were given a collection of egg mimics, some marred with the spiral bacteria. The octopuses tended to these false eggs for a while, except for those bacterially marked as ‘bad eggs’, which were quickly discarded.
The researchers were even able to identify which specific molecules the octopuses responded to. This chemical ‘language’ is enabled by molecules that, despite the submarine environment, are not readily washed away from the surface on which they are formed.
While the research focuses on octopuses, Sepela and her colleagues believe this sort of chemical signaling may apply to many other kinds of microbiomes; even our own.
“This might seem like a very specific case… but what we’re seeing is actually a general rule about how organisms sense microbiomes,” says Harvard cell physiologist Nicholas Bellono.
“Across life, evolution, and organ systems, microbes are essential – and this study shows another example of how deeply they influence physiology and behavior.”
This research was published in Cell.