Lonely Drunk Crayfish

Your (Belated) Random Science News Story From the Month of April

You might think that getting inebriated is a uniquely human one. You’d be wrong. Bees drink fermented nectar to the point where they “can’t find their way back to the hive, bang into trees or simply fall to the ground“. Bohemian waxwing birds eat fermented berries to the point of getting sent to rehab. 1 in 5 velvet monkeys prefer alcohol over water, at least according to a study of 35 of them…Animals like their booze, too.

As amusing as it may be to watch drunken honeybees ruin their waggle dances, scientists actually study the effects of alcohol – that is, the chemical ethanol – on simpler life forms in an attempt to understand how it affects us.

That’s why we now know that crayfish forced not to socially interact with others of their species hold their liquor better than their “gregarious” counterparts.

Procambarus_clarkii
Wikimedia Commons, Public Domain

You can read the results yourself in the open-access JEB article, here.

What happened?

The University of Maryland’s Jenz Herberholz, Matthew Swierzbinski, and Andrew Lazarchik wanted to study how ethanol affects the nervous systems of “juvenile” crayfish,1 and how that manifests in behavior. Specifically, they were looking at whether or not social history affects intoxication.

This is kind of the opposite of most of the previous research looking at social situation and intoxication. For example, squirrel monkeys (and rats) lower in rank have been observed to drink more than their social superiors, and cynomolgus monkeys (and rats) forced into individual housing drink more than those housed in groups. So, instead of how social situation affects how much crayfish drink, Herberholz and team were looking at how social situation affects crayfish reaction to how much alcohol is in their systems.

To do this, Procambarus clarkii were housed in a large (76x30x30 cm) communal tank – a population between 50-100 – and either kept there until the day of testing, or placed in isolation (15x8x10 cm tank) 7-10 days before testing. All crayfish that were selected for the experiment were weighed and measured immediately prior to placement in an isolation tank filled with a mixture of “200 Proof Ethyl Alcohol” (aka 100% ethanol) and deionized water. The ‘loner’ crayfish were all exposed to a 1 mol/L concentration – that’s about .058% ethanol by volume – but the ‘social’ crayfish got either 0.1 mol/L (15 of them), 0.5 mol/L (16) and 1 mol/L (24). For each crayfish, they timed the onset of different behaviors associated with intoxication, like tail-flipping (“short swimming sequences mediated by rapid flexions of the abdomen”) and the inability to “immediately” right itself after landing on its back (i.e. assuming a “supine position”).

After being observed to be properly drunk, they were thrown in a large heated skillet with some onions and garlic butter – probably some kind of herb, too – then served to the researchers on top of a nice bed of alfredo-ed linguine. Sorry, I’m hungry…They were put back in a tank of solely deionized water and got back to normal behavior after a couple hours.

Secondary experiments looking at the anatomical (i.e. nervous system) responses2 were also conducted. These crayfish either underwent surgery prior to experimentation to put in electrodes that stimulate neuron activity leading to the previously-mentioned tail flipping (The aim – to see how much electricity was required to activate the action), or got their abdomens completely cut off (or, merely had all their muscles in the abdomen removed, depending on the test) and had axons “impaled”, which sounds absolutely delightful.

What’d they find?

Unsurprisingly, the more highly concentrated the alcohol solution, the more quickly the crayfish exhibited intoxicated behavior:

  • For tail-flipping: 20 min for the 1 mol/L solution, 45 minutes for the 0.5 mol/L solution, and 106 min for the 0.1 mol/L solution (These, of course, are averages).
  • For the supine position, the times were 36 min, 72 min, and 162 min, respectively.
  • Of the crayfish exposed to the lowest concentration, 9 never were observed tail-flipping, and 12 never ended up on their backs during the 180-minute observation maximum.

As for the social aspect, the average time to observe tail-flipping and supine positions were 28 and 43 minutes, respectively. Based off the amount of data collected, the difference between these times and those of the non-isolated crayfish (in the 1 mol/L solution) are statistically significant. As the paper concludes,

“This result indicates that crayfish from an environment that provides opportunities for frequent interactions with other conspecifics are more sensitive to acute alcohol exposure than animals that are depleted of any social interactions for 1 week.”

In other words, lonely crayfish don’t get drunk as fast.

Through the secondary experiments the researchers were able to show that the observed changes in behavior could be directly tied to changes in the level of ‘excitability’ of the nervous system.

The researchers hypothesize that different social environments cause lasting changes3 in the neurotransmitter systems that alcohol interacts with, and these changes affect which receptors the ethanol molecules decide to target.

Thus, acute alcohol exposure affects individuals differently because their nervous system changes according to their social environment, which alters the interactions between alcohol, brain receptors, neural activity and corresponding behavior.

So what?

This is yet another study seeking to provide answers to how exactly ethanol interacts with the nervous system. Other drugs (both of the legal and il- variety) target very specific receptors; ethanol doesn’t, so it’s a much more complicated puzzle.

Even though crayfish are only crustaceans – and therefore in a completely different taxonomic phylum than humans – this result begs the question of whether or not a similar biological system is at least partly responsible for the drinking habits we observe in our own species. Does social exclusion cause humans to drink more because ethanol doesn’t affect them as quickly? The paper authors say even if the crayfish results don’t perfectly correspond to those in humans (or mammals in general), they can at least “contribute to the development of better options for the treatment and prevention of the negative consequences of alcohol abuse” – especially because other studies have shown crayfish display drug-seeking, withdrawal, and tolerance behaviors.

 

While we wait for more research in this area, let’s all pour one out for all those poor creatures that got their butts cut off in the name of science.


1. Otherwise known as crawfish, otherwise known as crawdads, etc. They’re basically tiny lobsters. 
2. Specifically, “Lateral giant interneuron threshold tracking” and “Intercellular recordings” 
3. How long it takes to cause said changes wasn’t tested – i.e. we don’t know the length of time a crayfish needs to spend isolated before its response to alcohol noticeably differs from its social peers. 

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s