Even without noses, octopuses are able to determine which food sources are good to eat and which have gone past their prime simply by touching them. The secret, says a new study, lies with surface microbiomes and some very sensitive suckers.
The study was carried out by a team working out of the lab of Nick Bellono, a Harvard biologist concerned with how organisms adapt to their environments on a molecular level. Previous research from the Bellono Lab revealed that octopuses – yes, that really is how you pluralize “octopus” – have chemical sensors in the suckers on their eight arms that let them effectively “taste by touching.”
Now, new work from the team adds even more information about how the cephalopods sense their world, particularly when it comes to detecting healthy compounds from unhealthy ones.
In a companion news piece in the American Association for the Advancement of Science (AAAS), Margaret McFall-Ngai, a physiologist and biochemist at the California Institute of Technology who was not involved in the research, called the study “the most breathtaking paper I’ve read in a long time.”
Bellono and fellow postdoc researcher Rebecka Sepela noted that California two-spot octopus mothers would regularly select and discard certain eggs from their own clutches. When examining the eggs under a scanning electron microscope, they found that the discarded eggs were covered in microbes.
This led to them to culture nearly 300 strains of microbes and experiment in ways in which the chemical they produce could activate the octopuses’ chemical sensors.
“The idea was, 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,” Sepela said.
Chemical translator
Sure enough, Sepela and her team were able to find the exact compounds that triggered the sucker-based receptors. For example, the team discovered that the bacterial species Vibrio alginolyticus produces a chemical called H3C on the decaying shells of dead crabs. When the team put that chemical on certain plastic toy crabs, the octopuses avoided those crabs, instead, trying to feast on the non-tainted versions.
The researchers also found that other microbes called Vibrio mediterranei appeared on octopus eggshells and produced a compound called LUM when the eggs aren’t viable. When the team created fake gel-based eggs covered in the substance, the octopuses tossed them out of their clutch, choosing to nurture the microbe-free eggs instead.
“The microbiome is acting almost like a chemical translator,” said Sepela. “It integrates environmental signals – like changes in temperature or nutrient levels – and outputs molecules that inform the octopus how to behave.”
While this particular study uncovered even more information about the mysteries of the octopus, the researchers feel that their finding could have implications in determining how microbiomes might affect the behavior of other species. We already know, for example, how our own internal microbiomes can shape things like depression and memory, so the team is curious to see how external microbial communities might steer the behavior of animals in the wild.
“The octopus gives us a way to study cross-kingdom communication with reduced complexity,” Bellono said. “It’s a system where we can link a microbial signal directly to a behavior – whether that’s predation or parental care.”
The study has been published in the journal Cell.
Sources: Harvard University, AAAS