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First published online April 18, 2008
Journal of Experimental Biology 211, 1355-1361 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.010165
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Behavioral and neural responses of juvenile crayfish to moving shadows

William H. Liden1 and Jens Herberholz1,2,*

1 Department of Psychology, University of Maryland, College Park, MD 20742, USA
2 Neuroscience and Cognitive Science Program, University of Maryland, College Park, MD 20742, USA


Figure 1
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  		Fig. 1. Experimental set-up and shadow velocities. (A) Top view of the experimental tank. Water containing food odor flows into a tunnel on the right side and exits on the left. Animals enter the tunnel from the start compartment and approach the food odor release point. A pair of bath electrodes is attached to the tunnel walls, 8 cm from the tunnel entrance. The bath is grounded with a ground wire. Shadows always move from right to left over the tank. (B) Side view of the set-up. Animals inside the tank are filmed with a camera positioned above the tank. The camera is connected to a TV monitor. Bath electrodes are connected to an amplifier and an oscilloscope. Signals are recorded on a computer. The shadow is produced by swinging a plastic rectangle through a light beam directed onto the tank. The tank wall facing the light and shadow apparatus is covered. (C) Average shadow velocities and accelerations derived from five repeated measurements with silicone photodiodes placed between the right tunnel wall and the bath electrodes. Velocities and accelerations for all three shadows (slow, medium, fast) are highly consistent as evidenced by small standard deviations.

 

Figure 2
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  		Fig. 2. Example of a tail-flip response and response patterns for different shadows. (A) An example of a tail-flip response of a crayfish exposed to a slow shadow. Shown are (1) the animal in the start compartment shortly after the experiment was started, (2) the animal in the tunnel walking towards the food odor release point and approaching the bath electrodes, (3) the animal producing a tail-flip in response to the shadow and (4) the animal in its final position after completing the tail-flip. (B) Patterns of behavior in response to shadows of different velocities. The number of tail-flips decreases with increasing shadow velocity while the number of stops increases. The differences in response pattern are statistically significant (*P<=0.01).

 

Figure 3
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  		Fig. 3. Electric field potentials recorded with bath electrodes during tail-flips. (A) An example trace of a tail-flip in response to a slow shadow. The action potential of the medial giant neuron (MG, asterisks; magnified in the inset) can be seen and enables non-ambiguous identification of the tail-flip as mediated by giant neuron activity. The large deflections that follow are field potentials generated by simultaneous muscle contractions caused by the giant spike. (B) A second example trace of a tail-flip in response to a slow shadow that is followed 43 ms later by a second tail-flip. The action potential of the MG neuron (asterisks; magnified in the inset) can be seen for the first tail-flip while the much smaller and less phasic potential for the second tail-flip is characteristic of field potentials caused by activity in the non-giant (Non-G; black arrow) circuit. See text for further explanation.

 

Figure 4
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  		Fig. 4. Comparison between crayfish that stopped and crayfish that tail-flipped in response to shadows. (A) Approach time, i.e. time to reach the bath electrodes after the experiment was started, does not differ between animals that later stopped or tail-flipped when exposed to shadows. Mann–Whitney test: P>=0.7. (B) Patterns of positions inside the tunnel for animals that later stopped or tail-flipped when exposed to shadows are not significantly different. Chi-squared test: P>=0.3. (C) Body orientation does not differ significantly between animals that later stopped or tail-flipped in response to shadows. Mann–Whitney test: P>=0.6. (D) The locations in the tunnel (past the bath electrodes) are not significant different between animals that later stopped and animals that later tail-flipped to the shadows. Mann–Whitney test: P>=0.4.

 

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© The Company of Biologists Ltd 2008