Octopuses given the powerful “party drug” MDMA get all cuddly with each other, new research shows.
Using molluscs to test the effects of an illicit substance more usually associated with all-night dance parties might sound initially like a prank by drunken marine biology students – or an attempt to revive the legacy of neuroscientist John Lily – but in this case the experiment had serious and valuable intent.
The research, conducted by Eric Edsinger of the Josephine Bay Paul Centre for Comparative Molecular Biology and Evolution, and Gul Dolen of Johns Hopkins University, both in the US, show that genetic and neural mechanisms governing social behaviours are conserved in both humans and octopuses – despite an evolutionary divergence of more than 500 million years.
To make their findings, Edsinger and Dolen took advantage of a 2015 study that succeeded in sequencing the genome of a species known as the California two-spot octopus (Octopus bimaculoides). Edsinger was a contributor to the project.
The full genome was found to contain a gene known as Slc6A4, which codes for a transporter of the chemical messenger serotonin. In humans, this messenger plays a crucial role in neurological wellbeing, helping to regulate the sleep-wake cycle. It is known to contribute to feelings of happiness, and, when in sub-optimal quantities, depression.
The serotonin transporter encoded by Slc6A4 is known as SERT. In humans, it is the primary site to which the chemical phenethylamine (+/-)-3,4- methylendioxymethamphetamine – better known as MDMA – binds.
Edsinger and Dolen have now shown that the same function persists in two-spot octopuses. This is interesting for several reasons, not the least of which is that for most of its life O.bimaculoides is a defiantly solitary animal. It associates with others of its species during a brief mating period – the only time when its behaviour can be described as “prosocial”.
To test whether this was a hard-wired behaviour or a consequence of environment – that is, whether the octopuses were antisocial because they were genetically programmed to avoid each other, or simply because they never encountered each other in normal circumstances — Edsinger and Dolen observed captive O.bimaculoides placed into tanks with other members of the species.
They discovered, contrary to expectations, that while males would avoid other males, they would spend more time than expected interacting with females. Direct contact, however, was limited to touching with a single tentacle.
Such interactions, however, could hardly be described as a love-fest. All that changed when the animals spent time in water containing MDMA.
Not to put too fine a point on it, the octopuses came over all huggy. As the researchers describe it: “after MDMA treatment, social interactions were characterised by extensive ventral surface contact, which appeared to be exploratory rather than aggressive in nature.”
This, suggest Edsinger and Dolen, implies that octopuses are in fact genetically programmed to be social, but that such behaviours are held in check “outside ethologically relevant periods, such as mating”. These constraints disappear when the molluscs are given a hefty dose of party drug.
And dosage was interesting. Despite the vast evolutionary gulf between mammals and molluscs, and the extremely different neurological systems at work in each phylum, for the octopi “effective doses of MDMA are in the same range as those described for humans and rodents”.
The results, the researchers conclude, mean that in future drugs intended for use in humans, if they bind to a genome site that is also conserved in molluscs, could be usefully tested on octopi.
The work is published in the journal Current Biology.