KEVIN GARDNER: Hi. My name is Kevin Gardner. I'm a senior here at Cornell, in the College of Agriculture and Life Sciences, and I am a biology major. And I work here in the Hopkins Lab, in the Department of Neurobiology and Behavior.
And what's really interesting about these electric fish is that they use electric signals, or electric pulses, that we call EODs, or Electric Organ Discharges, for two main reasons. One, they use them to communicate with each other, kind of like a Morse code, you can think of it as. And specifically what I am interested in is the behavior and the communication in agonistic interactions in males in this species.
So what I'm looking for is one, whether or not males in the species display territoriality during these agonistic interactions; and two, I'm looking at what exactly are the different communication signals that we see during these interactions? And we call these signals Sequence of Pulse Intervals, or SPIs for short. So we're trying to see if there are any stereotyped signals that we always see during these male to male agonistic interactions.
So welcome to our fish room. This is where we actually conduct our experiments, in my case, the male agonistic interactions. And what we have here, you can see, is our fish tanks here divided up into different sections. You can see A, B, and C. And what we have are obviously some hiding places and things like that for the fish in the tanks.
And then what we also have in each of these sections is an electrode. So if you were to look here, you can see these carbon electrodes that we use to monitor the electrical activity of these fish. Now, one of the unique things about these fish is they're actually nocturnal, which makes it obviously a little more difficult to monitor their behavior during our experiments.
So what we have to counter this is we have infrared lighting that you can see up here. So what that means is we turned on those infrared lights, and then we actually turn off our overhead lighting here. And we can monitor the fish's activity by using our camera, which can pick up infrared light using its night vision mode. So we're able to monitor these fish while they're active when the lights are off.
We have all of the males be isolated in individual sections, say sections A, B, or C. And the purpose of that time period is that we hope the males will come to recognize that section as their own home territory. Then, after the isolation period of two weeks is up, what we do is we allow the fish to interact freely for the first time. And during this time, we record both their motor behaviors and also the electrical behaviors, and you're looking for those signals during this fighting and when they're settling the dominance disputes.
So in this clip, what we're going to see here is at the top, you're actually going to see a video of the motor behavior of this fish. And we've labeled the dominant and the subordinate. And the dominant is this blue fish here, and the subordinate is the red fish on our left. What we're going to see below the video, scrolling in real time, is the actual electrical behavior of these fish.
And what we're going to see is essentially a plot of the frequency on a y-axis here versus the time on our x-axis. And obviously the higher we go up, the higher the frequency. And what we're going to see with this LRAD, which will be these red dots when we play it, you're going to see them have very high frequency, and modulate that frequency very rapidly.
And we're actually going to be able to hear this when we play the video. So here we go. And what's going to happen is our dominant is going to come over and attack the subordinate. And immediately upon being attacked, the subordinate will begin discharging this long, repeated acceleration-deceleration [ELECTRICAL NOISE]
All right. So another display that we saw was a display that we called pulse pairing. And this display we saw from the dominant male, as opposed to the LRAD which we saw from the subordinate males. And we saw this pulse pairing oftentimes when the dominant was simply patrolling around the tank, or when he was actually actively attacking the subordinate.
And what this display consisted of was it consisted of two EODs really close together, those Electric Organ Discharges, the electrical pulses. The dominant would fire two of them really close together, so duh duh. Then he would pause and repeat that. So, duh duh, duh duh, duh duh. And he would repeat this pattern over and over again. And we called this pulse pairing, just because we had those pairs of pulses repeated over and over again.
So what we're going to see in this clip is our, once again, dominant labeled in blue, and our subordinate. And we're going to see the dominant actually displaying these pulse pairs which, when we look at it on the frequency versus time plot, shows up as these two banding patterns that you can see there.
And that's just, once again, because we have two pulses close together, and then we have a pause. So we get these two bands of frequency. So we can see this when we actually play it here. [ELECTRICAL NOISE]
All right. So in this clip what we're going to see is actually some of the courtship behaviors that I was talking about before. And what we're going to see is the female, here labeled in red, will go up and actually elicit the male, who is in the upper right hand corner of the tank. The male will then proceed to swoop down, and the male will discharge an SPI, or a sequence of pulse intervals, called a creak.
And this was discovered by a student in this lab, Ryan Wong, a couple of years ago. And directly after what we call a creak, you will see the actual spawning behavior of these two fish. So here we go. [ELECTRICAL NOISE] Here's the creak that we were talking about. [ELECTRICAL NOISE] So that's a very nice illustration of both the motor and the electrical behaviors that we see during these courtship behaviors.
Well, the importance of this research is twofold. First, these electric fish, their communication method-- that of electric communication-- is a modality of communication that hasn't really been studied as extensively as, say, visual communication or audio communication. So it's really important that we study this modality in addition to those others.
And two, what's really significant about these fish is their nervous system is-- what's the best way of saying it? We can really have a good insight into the operation of their nervous system by looking at these electrical displays. And the reason for that is for every firing of their electro-motor neuron, we see one of these EODs, or electric organ discharges.
So it's just in a one to one ratio there. As opposed to, say, my voice right now, there are a lot of different neural inputs that make me be able to speak. But with these fish, it's much more simplified. So we can use the displays that I view and these studies where other people have viewed, and then we can take that and try to figure out what exactly is happening in their nervous system to produce that.
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Cornell student Kevin Gardner explains the experiment he's conducting in the Hopkins Lab to study agonistic behavior (i.e., aggressive or defensive actions like fighting and fleeing) and sequences of pulse intervals in the 'electric' mormyrid fish Brienomyrus brachyistius.
Gardner is a biology major in the College of Agriculture and Life Sciences.