Callinectes sapidus (Atlantic blue crab) is an endangered invertebrate. It has recently been discovered by Ram? et al. (PNAS 101: 11857-61, 2004) that crayfish sleep, a state during which they are relatively insensitive to stimulation, and their electroencephalogram (EEG) shows a slowing of activity similar to that of vertebrates. If the crabs sleep, then understanding its sleep patterns would be significant in understanding how to help these invertebrates survive in their natural habitat.
The 21st Century Biology class at Sidwell Friends School is a research oriented course. The blue crab is a good model for classroom use because they are hardy and fairly easy to maintain in the lab. We are studying crabs throughout their development from zoea to megalop to crab stages. We have set up a continuous video recorder to monitor the crabs' behavior throughout a 24 hour light-dark cycle, and are using continuous EEG recordings from electrodes inserted near the crab brain to analyze their neurological activity. Digitized video is stored on a computer and then played back at compressed time scales for reviewing and scoring of crab activity. EEG signals are filtered and digitized with an analog to digital converter, stored on computer, and the frequency content of the signal is analyzed over time with a windowed Fourier transform. The behavior scoring and frequency content of the EEG are then compared. If apparent sleep is characterized, the threshold to vibratory stimulation will be tested during putative sleep versus awake states. This work is being done in collaboration with scientists at George Mason University.
If we succeed in discovering sleep in crabs, this would add evidence to the hypothesis that sleep evolved early on in evolution, which would be important in discovering how and when sleep became evolutionarily important to higher taxa. One suspects that if blue crabs sleep, the ones that sleep deeper and longer are more vulnerable to predation, as they would be relatively helpless and insensitive to danger in such a state.