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In this De-Natured segment of Nature League, Brit breaks down a recent scientific journal article about the effect of MDMA on social behavior in octopuses.

Article citation:

Edsinger, E. and Dölen, G.

A Conserved Role for Serotonergic Neurotransmission in Mediating Social Behavior in Octopus

Current Biology, 2018

Article link:
https://www.cell.com/action/showPdf?pii=S0960-9822%2818%2930991-6


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On Nature League, we spend the third week of each month exploring a current trending article from the peer-reviewed literature.

Scientific information isn’t just for scientists- it’s for everyone! It just requires a bit of a break down. [CHEERY INTRO MUSIC].

For this month’s De-Natured segment, we’re going to look at an article released in September 2018 in the journal Current Biology. In this month’s Lesson Plan, we talked about the different ways that organisms send and receive signals. We discussed the main categories of communication, which are auditory, visual, tactile, and chemical, and we also touched on some behaviors that help facilitate these types of communication.

For many species, social behaviors in particular are a huge factor in communication between individuals. In fact, even asocial species that spend the majority of their time alone will briefly suspend that asocial behavior to allow things like mating. Cause...y’know...gotta do what you gotta do...

In this paper entitled, “A Conserved Role for Serotonergic Neurotransmission in Mediating. Social Behavior in Octopus”, scientists from a marine lab and a medical school teamed up to explore a very unique aspect of social behavior- specifically, the role of social behavior heightening chemicals in an asocial octopus. Let’s start by breaking down the title. “A conserved role” as stated in the article title has to do with the conservation of a certain mechanism.

In biology, a conserved role of some molecule is one that persists over time, and across different species. How about “serotonergic neurotransmission”? Neurotransmission is when neurons, or nerve cells, release signals called neurotransmitters to communicate with other neurons.

Serotonergic neurotransmission is when serotonin is the neurotransmitter involved. So all together, the title is describing a persistent and shared mechanism of serotonin and other chemicals affecting social behaviors. Moving on...

So what’s already known? Well for one, scientists estimate that humans and octopuses are separated in evolutionary time by more than 500 million years. However, we share more in common than one might imagine.

For example, octopuses are insanely smart. They exhibit all kinds of problem solving skills, and anyone who’s worked at an aquarium can tell you that these guys get into constant trouble, whether it’s escaping from enclosures or shooting passerbys with water. In this particular study, the researchers wanted to find possible evolutionary links between social behavior in humans and in octopuses.

Despite our differences in body plans and nerve tissue organization, both vertebrates and invertebrates demonstrate complex, social behaviors. What’s more, these social behaviors are party regulated by the neurotransmitter serotonin. Even though vertebrates and invertebrates might seem really different on the outside, our social behaviors are regulated by some shared chemicals.

This means that the prosocial functions of serotonin might be conserved evolutionarily. This possibility led the team to investigate if we might have some genes in common with octopuses when it comes to social behavior. Here’s where the study gets admirably creative.

They wanted to investigate prosocial behaviors, which are behaviors that generally help or benefit others- like cooperating, donating, or sharing. It just so happens that prosocial behavior in humans goes up big time with the help of a chemical called methylenedioxymethamphetamine, or MDMA. This chemical is so efficient in humans that some people use it as a recreational drug.

In these cases, it’s also called ecstasy for...obvious reasons. Scientists know which parts of the human genome are affected by MDMA, so this team set out to sequence these regions in the California two-spot octopus. Note that this species is asocial, and only really exhibits social behavior during mating, so there wasn’t any obvious reason to suspect any conserved machinery between humans and this species.

However, some regions of the octopus gene sequence for SLC6A4 perfectly lined up with that of humans. The importance here is that this gene is part of the machinery that helps bind both MDMA and serotonin. They also found that in this same region, the amino acids that aid in MDMA binding in humans were completely conserved in this octopuses genome.

It’s one thing to know that the genetic material is similar, but it’s another thing to see it in action. The team now wanted to observe the behaviors of these normally asocial octopuses to the drugs that boost social behaviors in humans. To demonstrate their experiment, let’s take a trip to headquarters!

To see if the effects of MDMA were conserved functionally, the researchers tested whether octopus exposure to MDMA would promote positive behaviors in response to an object that typically causes aversive behaviors. They set up a social task experiment with three separate chambers. In earlier experiments, the team demonstrated that octopuses of this species preferred female social objects significantly more than male social objects.

With this in mind, they observed how octopuses approached a male social object with and without. MDMA. The three chambers were interconnected and set up like this: the center was empty, one side had a novel object, and the other side had a male social object.

For our purposes, we’ll call these the object, center, and social chambers. The experiment was observational, and went like this. They placed an octopus in the enclosure for 30 minutes and recorded the amount of time spent in each chamber.

Then, between 5 and 24 hours later, they exposed the test octopus to MDMA, and then into the tank it went for another 30 minutes. Once again, the scientists recorded how much time the octopus spent in each of the three chambers. So here’s what they found.

The octopuses spent significantly more time in the social chamber while on MDMA when compared to pre-MDMA exposure. Not only that, but the nature of the interactions were different as well. Without MDMA, when the octopuses interacted with the social object, direct contact was rare, and at most included reaching and touching of a single arm.

Well, I bet you can guess where we’re headed next. After MDMA exposure, octopus interactions with the social object were much more involved, and included extensive surface contact. A nd while this might all seem a bit absurd, the results of the experiment provide some scientifically relevant points.

For the first time, there’s evidence that the prosocial effects of MDMA that we observe in humans are conserved in an octopus, despite us being such different organisms on the surface. Despite being published in a prestigious peer-reviewed journal, I think the reason this study has gained so much traction in the public sphere is because on the surface level, the premise is just plain /strange/. This study showed up in most of my academic and non-academic circles the week it came out.

I had friends post it to my wall on Facebook; I saw it trending on popular science news sites; I definitely came across it on Twitter; and even the mainstream news media got ahold of it. And while the research itself is solid and commendable, the general topic and methods pretty much let the headlines write themselves. For better or worse, the absurd makes a good news story, and in this case, the idea of octopuses on party drugs was just bizarre enough to make it a shareable favorite.

Headline potential aside, there’s another reason why I think this study was shared so broadly. One part of the human condition is interacting with other species on Earth, and humans in general seem to enjoy seeing themselves in non-human animals. It reminds us that we’re connected not only in space and time, but in terms of the very chemicals that make us do the things we do.

As with any piece of new research, there are several areas of improvement that exist in this study for follow-up research. My first issue with the study is the sample size. For the MDMA behavioral observation experiment, they only had four octopuses do the task.

This doesn’t allow a lot of room when in comes to statistical tests, and although the team reported significant differences, a larger sample size is badly needed in subsequent studies. That said, the authors directly state that this study is the first step of a larger research program, and that these are only preliminary results. Fair enough.

However, another spot of potential contention is that the entire purpose is medical in nature. In their concluding statement the authors state that these results are a first step toward developing octopuses as model organisms. This means that the applications of the research will be more testing on non-humans animals for human purposes, which could potentially be an issue when it comes to ethical considerations.

Whether the information is used to help humans or not, the fact remains that it is simply incredible for such different species to have the same genetic machinery and behavioral responses to the same drug. It reminds us that 500 millions years of separation, and having a backbone or not doesn’t mean we’re all that different. If this is conserved across the animal kingdom, who know what other similarities we’ve yet to discover.

Thanks for watching this episode of De-Natured here on Nature League. Nature League is a Complexly production: check out this episode from our sister channel SciShow if you’d like to learn more about the intelligence of octopuses.