Lobster signaling

This section reviews the complex currents lobsters generate to eliminate metabolites and broadcast chemical signals and the return currents from which they obtain chemical signals and metabolic energy. Lobsters are examples of hard-shelled animals that store urine and feces, allowing them to be chemically "quiet" when necessary. 

Together, the two lobster-generated currents that can be measured around the animal s anterior end are complex and carefully controlled. They are ideally suited to carry urine, urine pheromones, and gill metabolites away from the lobster to specified directions. Simultaneously, the water displaced by these outgoing currents results in incoming currents with chemical signals from the environment that can be sampled by the antennular chemoreceptors. 

All indications are that we are only just beginning to see a few threads of the rich fabric of chemical signals that link lobsters to each other and to their environment. Exoskeleton, bladders, glands, and control of currents all indicate that these animals can be chemically quiet and release specific signals at critical times during aggression and courtship. Chemical signals appear to be used to remember individuals and to facilitate stable dominance hierarchies. 

One may wonder why lobsters appear to use urine as a dispersal solvent for chemical signals, whereas terrestrial arthropods such as the well-studied insects use direct release of gland products into the air. Perhaps the answer is that small animals in air (such as insects) are always in danger of desiccation. By contrast, marine lobsters and crabs are relatively large and may experience only minor water loss problems due to osmosis. Thus, it may not be difficult for a 500-g lobster to store 10 ml of urine and release it during a dominance battle at a rate of up to 1 ml/min (27). The advantage of urine-carried pheromones is that the dispersal mechanism already exists urine is injected into the gill current, which in turn injects into ocean currents. 

Stream. Lobster, tail-waving newts, and possibly fanning fish produce information currents that propel chemical signals toward recipients. In the lobster, the female sends a current with pheromone into the male s shelter. The male, in turn, draws water toward himself and fans it out into the surroundings, signaling his mating status (Atema, 1986). 

A radiation-induced signal can be detected in the exoskeleton of Norway lobster (Nephrops norvegicus) (Stewart etal., 1992) and other species of prawn and shrimp (Morehouse and Desrosiers, 1993). In the case of Norway lobster, the signal in both irradiated and unirradiated cuticle is complex because of the presence of the six resonance peaks due to Mn2+. In the irradiated samples there is an additional free radical peak in the centre of the Mn2+ signal at 349.5 mT (Figure 6). This signal is more easily seen when the... 

Figure 7. Effect of processing on the radiation-induced EPR signal in Norway lobster cuticle. (From Stewart et al.. 1993bl.

The shape of the radiation-induced signal was similar in different components of the exoskeleton of Norway lobster but the intensity of the peak varied (Stewart etal., 1993a). Consequently, the part of the cuticle used for EPR analysis will not affect identification of irradiation treatment but could influence the estimation of dose in samples of unknown processing history. 

Stewart, E.M., Stevenson, M.H and Gray, R. (1993a) The effect of irradiation dose and storage time on the ESR signal in the cuticle of different components of the exoskeleton of Norway lobster (Nephrops norvegicus) Appl. Radiat. Isot. 4, 433. 

Crustaceans are known to use pheromones in behavioral contexts other than avoidance, including reproduction and social interactions. For example, at least one spiny lobster, the California spiny lobster Panulirus interrupts, has been shown to be attracted to the odor of conspecifics.131 This pheromonal phenomenon is taken advantage of by workers in the lobster fishery, who use live lobsters as bait in their pots.132 However, relatively little research has been performed on the topic of aggregation pheromones, including the nature of the signal and its sensory reception. Pheromonal chemical signals are also involved in the establishment and maintenance of social hierarchies in crustaceans.133 134... 

Fadool, D. A. and Ache, B. W., Plasma membrane inositol 1,4,5-trisphosphate-activated channels mediate signal transduction in lobster olfactory receptor neurons, Neuron, 9, 907, 1992. 

While experimental evidence concerning the molecular mechanisms and the diversity of reaction cascades involved in olfactory signal transduction in antennal cells of insects is still fragmentary, a much more detailed picture has been established for signal transduction in chemosensory cells of the lobster, another member of the arthropod phyla. The bipolar chemosensory neurons of the lobster antennule respond to stimulation with odorous compounds either with an excitation or an inhibition i.e. cells are equipped to respond to one odor with a depolarization and excitation as well as to another odor with a hyperpolarization and inhibition. 

The existence of a variety in response kinetics and excitatory and inhibitory responses in the same ORN are not easily explained in terms of a single signal transduction cascade. They hint at the possibility of multiple transduction pathways, as has been demonstrated in lobster ORNs (Ache and Zhainazarov, 1995). This could lead to simple forms of stimulus integration at the level of the ORN (Derby, 2000). Do multiple pathways function in complete isolation or is there crosstalk The presence of a variety of reversal potentials in patch clamp studies of Drosophila antennal ORNs suggests that odorants do not all elicit the same transduction mechanism (Dubin and Harris, 1997). What is the evidence in Drosophila for the presence of transduction element of the main pathways, the cyclic nucleotide pathway and the IP3/DAG pathway Is there coexpression in single neurons ... 

Figure 4.6. Absorbance-over-time for cobalt in the TORT-2 Lobster Hepatopancreas CRM at 240.725 nm using HR-CS ET AAS gray line uncorrected signal black line corrected signal (from Ribeiro et al. [14]).

Effect on the Central Nervous System. Perfusion of the central nerve cord with 10 7 M avermectin eliminated the nerve excitation induced by y-BHC (10 6 M) (44). Within 15-20 min after perfusion of avermectin the nerve became completely calm. Under the experimental conditions a few random single spikes per minute were observed but only in the control nerves. Avermectin completely eliminated such background signals. Shortly before transmission blockage occurred, the nerve treated with y-BHC and avermectin showed severe but transient excitation. Recently Mellin et al. (49) observed an initial enhancement by avermectin of the facilitation response of excitatory postsynaptic potentials to a train of stimuli in the stretcher muscle of the lobster. Nerve excitation by DDT (10 5 m) was also found to be eliminated by avermectin (10 7 m). 

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