The sensory abilities of vertebrates and invertebrates are generally more similar than they are different: both groups can detect light, sound, pressure, and so on. One of the few cases of a sensory ability that seemed to be the domain of vertebrates alone was the ability to detect electrical signals: electroreception. Several fish have it, and use electrical signals to communicate. Platypus have it. Electric signaling in fish is a classic examples of behaviour understood at the neural level.
For a long time, people argued that invertebrates don’t have electroreception, for reasons that were perhaps a bit idiosyncratic. One explanation I heard given was that something like a crayfish was too small. And I’ve seen crayfish much bigger than knifefish.
A few years ago, a couple of papers came out that started to pick apart that idea, and showed that crayfish could respond to electrical signals. This new paper by Patullo and Macmillan* pushes the state of the art forward in a couple of ways (And it does so with some rather graceful prose, I might add.)
First, it expands the number of species. The authors used Cherax destructor, which they’d used in a previous study, and also tested Cherax quadricarinatus (pictured). Both species decreased their activity in the presence of electric fields, at about the same intensity levels.
The intensity levels were the second way this paper pushed things forward: it showed that crayfish were responding to much lower levels of electricity than previous studies – about ten times lower. Because neurons run on electricity, if you give an intense enough signal, animals will respond, even if they have no specialized sensory apparatus for detecting electical fields. This paper goes further towards suggesting that crayfish can respond to a biologically relevant electrical signal. And, indeed, one of the key features is that the electrical signal played to the crayfish was derived from a swimming tadpole, which crayfish will prey upon.
These experiments seem rather tricky to pull off and calibrate. Behavioural analysis is complicated by there not be any particular behaviour identified (yet!) that is reliably and consistently evoked by an electrical signal. This is going to make the next stage of this research, locating the neurons responsible for crayfish electroreception, a challenge.
* Full disclosure: I have worked with both authors on this paper, so I think of them as Blair and David. And, as an example of how long it takes to get things out in science, I helped them start this project over ten years ago.
Crossposted at Marmorkrebs blog.
Patullo, B., & Macmillan, D. (2010). Making sense of electrical sense in crayfish Journal of Experimental Biology, 213 (4), 651-657 DOI: 10.1242/jeb.039073