Great moments in crayfish research: Serotonin, octopamine, and social status

The paper is usually remembered as using lobsters, probably because many of the later papers springing from it used lobsters. But there were crayfish in there too, and I have the photographic evidence to prove it.


These two pictures show good old Louisiana red swamp crayfish, Procambarus clarkii, the lab rat of the crustacean world. The animal on the left is in a pose that would normally be associated with an aggressive animal, one gearing up for a fight. The animal on the right is in a pose that would normally be associated with, “Please don’t kill me.”

Crayfish fighting has been consistently studied for over half a century (Bovbjerg 1956 is a seminal paper), and are a fairly well used model for aggression. There are many reasons for this, but one is that crayfish will fight early, often, and for no reason. They fight when they are small, so the behaviour is completely “hard wired.” They fight if there is no food, shelter, or mating opportunities at stake. Fighting is just something they do.

Now, we normally think of fighting as a fairly complicated behaviour. You have to assess your opponent. Make tactical decisions to continue on the fight or leave. Thus, you would think that finding a way “into the system” would be quite tricky.

That’s where the experiment pictured above comes in. The crayfish shown are not animals that are in a fight. instead, they have been injected with the neuroactive chemicals. The individual on the left has been injected with serotonin (also known as 5-hydroxytryptamine, or 5-HT). The individual on the right has been injected with octopamine.

What looked to be a potentially intractable problem involving many neurons was simplified and made tractable at a stroke. It now appeared that crayfish – and other similar decapod crustaceans – had a couple of fairly simple “master dials” on their behavioural control panel relating to aggression and social status. And those fairly simple dials were things that experimenters could use to fiddle with the system. Finding out that simple injection of these chemicals mimicked some important aspects of fighting behaviour paved the way for many later papers.

References

Bovbjerg RV. 1956. Some factors affecting aggressive behaviour in crayfish. Physiological Zoology 29: 127–136.

Livingstone MS, Harris-Warrick RM, Kravitz EA. 1980. Serotonin and octopamine produce opposite postures in lobsters. Science 208(4439): 76-79. doi: 10.1126/science.208.4439.76