upright=1.5|thumb|right|Animated representation of lobstering.

The caridoid escape reaction, also known as lobstering or tail-flipping, is an innate escape behavior in marine and freshwater eucarid crustaceans such as lobsters, krill, shrimp and crayfish.

The reaction, most extensively researched in crayfish, allows crustaceans to escape predators through rapid abdominal flexions that produce powerful thrusts that make the crustacean quickly swim backwards through the water and away from danger. The type of response depends on the part of the crustacean stimulated, but this behavior is complex and is regulated both spatially and temporally through the interactions of several neurons.

Discovery of the first command neuron-mediated behavior

thumb|left|The tail-flip escape behavior was first described in the crayfish [[Procambarus clarkii]]

In 1946, C. A. G. Wiersma first described the tail-flip escape in the crayfish Procambarus clarkii and noted that the giant interneurons present in the tail were responsible for the reaction. The aforementioned neuronal fibres consist of a pair of lateral giant interneurons and a pair of medial giant interneurons, and Wiersma found that stimulating just one lateral giant interneuron (LG or LGI) or one medial giant interneuron (MG or MGI) would result in the execution of a tail flip. Wiersma and K. Ikeda then proposed the term "command neuron" in their 1964 publication, and applied it to the giant interneuron's ability to command the expression of the escape response. This was the first description of a command neuron-mediated behavior and it indicated that the depolarization of a neuron could precipitate complex innate behaviors in some organisms.

This concept was further fleshed out with more specific and stringent conditions in 1972 when Kupfermann and Weiss published The Command Neuron Concept. The paper stated that command neurons were neurons (or small sets of neurons) carrying the entire command signal for a natural behavioral response. According to the authors, command neurons were both necessary and sufficient in the production of a behavioral response. The concept of command neuron-mediated behaviors was both ground breaking and controversial, since determining command neuron-mediated behaviors was a problematic process due to difficulties in understanding and interpreting anatomical and behavioral data.

Research with crayfish

Behavioral neurobiologists in the field of neuroethology have researched this behavior extensively for over fifty years in the crayfish species Procambarus clarkii. The type of escape response depends on the region of the crayfish that is stimulated but all forms require abdominal contractions. When a strong, unpleasant tactile stimulus is presented, such as a burst of water or the prod of a probe, a stereotyped behavior occurs in which the muscular tail and wide tail fan region of the telson are used like a paddle to propel the crustacean away from harm using powerful abdominal flexions. The entire process occurs in a fraction of a second as movements are generated within two hundredths of a second (20 milliseconds) from the original trigger stimulus and the period of latency after a flexion is a hundredth of a second (10 milliseconds).

Anatomy involved

Like other decapod crustaceans, the crayfish possesses a hard, segmented exoskeleton that reflects muscular and neural segmentation. The anterior portion of the crayfish is the cephalothorax region. The region rostral to the cephalic groove, which separates the head and thorax region, is characterized by the presence of eyes, antennae and claws while the region caudal contains four pairs of walking legs. This is the crayfish's primary mode of locomotion. Their projections extend through the third root in each ganglion, and Furshpan and Potter found that the synapses they subsequently made with the MoG passed depolarizing currents in a direct and unidirectional manner. These electrical synapses account for the speed of the escape mechanism and display some features of chemical synapses such as LTP and LTD.

Non-giant escape often occurs during situations where lateral or medial giant-mediated escape may not be beneficial or during times where those behaviors are suppressed. This allows the crayfish to attack offenders, escape during feeding, or wriggle free when it has been restrained by the carapace.

Lateral giant-mediated escape

The lateral giant (LG)-mediated escape mechanism is the most extensively analyzed form of the tail flip. The LG is not actually one neuron, but rather a group of closely associated neurons arranged end to end and connected by electrical synapses (also called septate synapses). As a result, the LGI functions as one giant, continuous neuron, such as the MG.

3 – Swimming

Non-giant-mediated responses are initiated after the tail flip, creating cycles of flexion followed by extension. This non-giant system is activated parallel to the LGI circuit when the hair cells receive input. However, this behavior has a longer delay that allows the onset of swimming to occur after the completion of the tail flip. The non-giant swimming occurs independently of the LGI response since direct stimulation of the LGI with the electrodes results in a tail flip but not the subsequent non-giant swimming. This swimming response seems to be a fixed action pattern mediated by a central pattern generator since it does not require sensory feedback for physical and temporal maintenance.

Learning

Repeated tapping of the abdomen leads to habituation of the tail flip mechanism. However, self–habituation is prevented by command neuron–derived inhibition because when a tail flip is begun, the mechanisms that induce habituation are repressed. The habituation occurs at the level of the A type and C type interneurons, which experience synaptic depression. The habituation process is also mediated further up the circuit through the buildup of tonic inhibition, brought on by the repeated stimulation. shrimp or prawn, which is the root of the name of the taxonomic infraorder Caridea, a large group of crustaceans also known as the caridean shrimp.

See also

  • Coincidence detection in neurobiology
  • Pain in crustaceans

References

Further reading

  • Roberts, A., Krasne, F. B., Hagiwara, G., Wine, J. J., and Krarner, A. P. (1982) "Segmental giant: Evidence for a driver neuron interposed between command and motor neurons in the crayfish escape system". Journal of Neurophysiology. 47: 761–781.
  • Wine, J.J. and Hagiwara, G. (1977) "Crayfish Escape Behavior I. The Structure of Efferent and Afferent Neurons Involved in Abdominal Extension". The Journal of Comparative Physiology-A 121: 145–172.
  • The Lobster Conservatory includes information on the biology and conservation of lobsters. The majority can be applied to crayfish due to common ancestry and homology.
  • Neural and tail anatomy provides an idea of the organization of the segmental ganglia in the tail of the crayfish. The second diagram on the page is a transverse section through the tail that highlights the positions of the LGI, MGI and non-giant neurons. At the bottom of the page it also has diagrams of the tail flips caused by stimulation of the LGI (on the left half of the diagram) and the MGI (on the right half of the diagram). This accurate diagram appears to be similar to that found in Wine and Krasne's 1972 publication.
  • Lobster Body Plan presents information on decapod anatomy.
  • Cornell University's Neuroethology Course page