Charles D. Derby

Morphology of the Brain of Crayfish, Crabs, and Spiny Lobsters: A Common Nomenclature for Homologous Structures

The morphologies of the cerebral ganglia (brains) of three infraorders of the decapod crustaceans (Astacura-crayfish; Brachyura-crabs; Palinura-spiny lobsters) are described. A common nomenclature is proposed for homologous nerve roots, brain regions, tracts, commissures, neuropils, and cell body clusters.

Chemically stimulated feeding behavior in marine animals : Importance of chemical mixtures and involvement of mixture interactions.

A review is provided of the chemical components in tissue extracts that elicit feeding behavior in marine fish and crustaceans. For most species, the major stimulants of feeding behavior in excitatory extracts are an assemblage of common metabolites of low molecular weight including amino acids, quaternary ammonium compounds, nucleosides and nucleotides, and organic acids. It is often mixtures of substances rather than individual components that account for the stimulatory capacity of a natural extract. Recent studies using a shrimp,Palaemonetes pugio, are described in which behavioral bioassays were conducted with complex synthetic mixtures formulated on the basis of the composition of four tissue extracts. These results indicate that synergistic interactions occur among the mixture components. The neural mechanisms whereby marine crustaceans receive and code information about chemical mixtures are also reviewed. Narrowly tuned receptor cells, excited only by particular components of food extracts such as specific amino acids, nucleotides, quaternary ammonium compounds, and ammonium ions, are common in lobsters and could transmit information about mixtures as a labeled-line code. However, since physiological recordings indicate that most higher-level neurons in the brain each transmit information about many components of mixtures, rather than about a single component, it is suggested that information about a complex food odor is transmitted as an across-fiber pattern, instead of a labeled-line code. Electrophysiological recordings of responses of peripheral and central neurons of lobsters to odor mixtures and their components reveal that suppressive interactions occur, rather than the synergistic interactions noted earlier in the behavioral studies. Possible reasons for these differences are discussed. Evidence from the behavioral study indicates that the “direction” of a mixture interaction can be concentration-dependent and the synergism may occur at low mixture concentrations, while suppression may occur at high concentrations.

Neural processing, perception, and behavioral responses to natural chemical stimuli by fish and crustaceans

This manuscript reviews the chemical ecology of two of the major aquatic animal models, fish and crustaceans, in the study of chemoreception. By necessity, it is restricted in scope, with most emphasis placed on teleost fish and decapod crustaceans. First, we describe the nature of the chemical world perceived by fish and crustaceans, giving examples of the abilities of these animals to analyze complex natural odors. Fish and crustaceans share the same environments and have evolved some similar chemosensory features: the ability to detect and discern mixtures of small metabolites in highly variable backgrounds and to use this information to identify food, mates, predators, and habitat. Next, we give examples of the molecular nature of some of these natural products, including a description of methodologies used to identify them. Both fish and crustaceans use their olfactory and gustatory systems to detect amino acids, amines, and nucleotides, among many other compounds, while fish olfactory systems also detect mixtures of sex steroids and prostaglandins with high specificity and sensitivity. Third, we discuss the importance of plasticity in chemical sensing by fish and crustaceans. Finally, we conclude with a description of how natural chemical stimuli are processed by chemosensory systems. In both fishes and crustaceans, the olfactory system is especially adept at mixture discrimination, while gustation is well suited to facilitate precise localization and ingestion of food. The behaviors of both fish and crustaceans can be defined by the chemical worlds in which they live and the abilities of their nervous systems to detect and identify specific features in their domains. An understanding of these worlds and the sensory systems that provide the animals with information about them provides insight into the chemical ecology of these species.

Learning from spiny lobsters about chemosensory coding of mixtures

Studies of the peripheral olfactory system of the Caribbean spiny lobster Panulirus argus and related decapod crustaceans have helped us understand mechanisms of coding of mixtures, some of which are discussed in this review. Although the number of cells in the lobsters olfactory system is much lower than in vertebrate olfactory systems, it is a highly complex system. The receptor neurons (RNs) of this olfactory system are complex processors that cannot be categorized into discrete cell types, but rather have a diversity of response profiles. Each RN can have different types of receptor proteins, second messengers, and/or ion channels, which undoubtedly contributes to the functional diversity of these neurons and makes them complex peripheral integrators. The RNs probably encode information about the quality of mixtures as a distributed or population code, providing a basis for behavioral discrimination of natural food stimuli. Analysis of distributed codes for a series of blend ratios of binary mixtures reveals that the qualities of individual compounds are probably not lost when mixed. Such peripheral processing allows spiny lobsters to perceive complex odors as a set of elemental cues if the salience of the components is sufficiently high.

Escape by Inking and Secreting: Marine Molluscs Avoid Predators Through a Rich Array of Chemicals and Mechanisms

Inking by marine molluscs such as sea hares, cuttlefish, squid, and octopuses is a striking behavior that is ideal for neuroecological explorations. While inking is generally thought to be used in active defense against predators, experimental evidence for this view is either scant or lacks mechanistic explanations. Does ink act through the visual or chemical modality? If inking is a chemical defense, how does it function and how does it affect the chemosensory systems of predators? Does it facilitate escape not only by acting directly on predators but also by being an alarm signal for conspecifics? This review examines these issues, within a broader context of passive and active chemical defensive secretions. It focuses on recent work on mechanisms of defense by inking in sea hares (Aplysia) and extends what we have learned about sea hares to other molluscs including the cephalopods.

The sensory basis of feeding behaviour in the Caribbean spiny lobster, Panulirus argus

A complex nervous system enables spiny lobsters to have a rich behavioural repertoire. The present paper discusses the ways in which the sensory systems of the Caribbean spiny lobster, Panulirus argus, particularly its chemosensory systems, are involved in feeding behaviour. It addresses the neural mechanisms of three aspects of their food-finding ability: detection, identification, and discrimination of natural food odours; the effect of learning on responses to food odours; the mechanisms by which spiny lobsters orient to odours from a distance under natural flow conditions. It demonstrates that the olfactory organ of spiny lobsters might use acrossneuron response patterns in discriminating odour quality; that the hedonic value of food can be modified by experience, including associative and nonassociative conditioning; that spiny lobsters can readily orient to distant odour sources; and that both chemo- and mechanosensory antennular input are important in this behaviour. Either aesthetasc or nonaesthetasc chemosensory pathways can be used in identifying odour quality, mediating learned behaviours, and permitting orientation to the source of distant odours. Studying the neuroethology of feeding behaviour helps us understand how spiny lobsters are adapted to living in complex and variable environments.

Functional organization of olfaction in crustaceans

Abstract Many of the stimulatory components of complex food odors for marine animals such as lobsters and crabs are common, low molecular weight organic molecules. Crustaceans possess very narrowly tuned receptor cells for these substances, which contribute to coding the quality and quantity of food-related odors. Activity evoked by odorant mixtures cannot always be predicted from responses to the individual components of the mixture; this general phenomenon, termed mixture interaction, is a result of events both at the primary receptor cells and in the CNS. With neurons at various levels of the olfactory pathway tractable for physiological, morphological and biochemical analyses, crustaceans provide useful animal models with which to study olfaction.

Chemoreceptor Cells in Aquatic Invertebrates: Peripheral Mechanisms of Chemical Signal Processing in Decapod Crustaceans

The sensory capabilities of any animal are determined by a sequential set of physical and biological filters that regulate which environmental disturbances will stimulate the receptive surface of the animal. The environment itself is the first filter as it transmits physical or chemical disturbances from one or another source. The animal’s sense organs contain additional physical filters that select—each with its own degree of specificity—which part of the disturbances will have best access to the receptor membrane. Subsequent filtering occurs at the level of receptor cells and at each next level of the CNS. Environmental disturbances that alter the activity of receptor cells are called stimuli: they include disturbances that trigger molecular mechanisms, such as adaptation in the cell without necessarily causing it to fire nerve impulses or other means of information coding. Subsequent interneuronal steps of information processing are all based on neural signals that code certain aspects of the original stimuli.

Functional units of a compound nose: Aesthetasc sensilla house similar populations of olfactory receptor neurons on the crustacean antennule

The lateral flagellum of the antennule of the spiny lobster Panulirus argus houses more than 1,000 morphologically similar olfactory sensilla, called aesthetascs. By using a high‐resolution activity labeling technique that depends on entry of agmatine into olfactory receptor neurons (ORNs) through cation channels during odor stimulation, we examined the distribution of different functional types of ORNs within and across mature aesthetascs. A significant number of ORNs in mature aesthetascs are labeled with agmatine during stimulation by single odorants, including adenosine‐5`‐monophosphate, ammonium chloride, cysteine, glycine, proline, and taurine. The percentage of ORNs per aesthetasc that was agmatine labeled during odor stimulation averaged 0.5–1.6% for single compounds and 4.6% for a 33‐component mimic of oyster tissue. For most antennules and antennular regions studied, the percentage of agmatine‐labeled ORNs by stimulation with single or complex odorants was statistically homogeneous across most or all aesthetascs. The extent of heterogeneity among mature aesthetascs was correlated with their age: extensive heterogeneity was observed only in the distal part of the flagellum containing the oldest aesthetascs and their ORNs. Thus, it appears that over most of the length of the aesthetasc‐bearing region of the lateral flagellum, different and distinct functional types of aesthetascs do not exist. Rather, aesthetascs appear to be repetitive morphological and functional units in olfactory coding. However, because odor sensitivity of ORNs can change with the age of an aesthetasc, some development‐related functional heterogeneity exists among aesthetascs. J. Comp. Neurol. 418:270–280, 2000.

Narrow-spectrum chemoreceptor cells in the walking legs of the lobsterHomarus americanus: Taste specialists

Summary1.The chemoreceptors in the legs of lobsters function in the localization and handling of food (Derby and Atema 1982b). Multi-unit neurophysiological analysis of these receptors has demonstrated that certain amino acids and amines are highly excitatory stimuli, some peptides and proteins are moderately excitatory, whereas carbohydrates, alcohols, nucleosides, and nucleotides are in general only slightly excitatory (Derby and Atema 1982a). By single-unit extracellular recording techniques, the specificity of single primary chemoreceptor cells is described here in detail.2.In contrast to what is known in vertebrates, narrow-spectrum chemoreceptors of several different types were found, each type responding with maximal sensitivity to only one of the following compounds: L-glutamate, L-glutamine, L-arginine, taurine, betaine, and ammonium chloride. Narrow-spectrum cells responsive to glutathione, hydroxy-L-proline, L-aspartate, glycine, and γ-aminobutyrate (GABA) were searched for but were not found.3.The most extensively studied type of receptor — thel-glutamate sensitive cell group — responded with less than 8% of thel-glutamate response to 25 other compounds at equimolar concentrations.4.Ammonium chloride sensitive cells were also highly specific. The most effective stimuli for these cells, other than ammonium chloride, werel-ornithine andl-citrulline; however, even at 3.5×10−4 M, these compounds were only 11.6% and 6.2%, respectively, as effective as 3.5×10−6 M ammonium chloride.5.The other groups of narrow-spectrum cells -l-arginine,l-glutamine, taurine, and betaine sensitive chemoreceptors — showed equally strong specificity. There is also evidence for a protein-best cell, which responded to hemoglobin but not to its enzymatically-digested components.6.There was one cell that did not fit the narrow-specificity response pattern. It responded to at least 7 of 15 compounds tested at 3.5×10−4 M, 4 of 15 at 3.5×10−5 M, and 3 of 15 at 3.5×10−6 M.7.These results indicate that the peripheral coding system in the legs of lobsters is based largely but perhaps not exclusively on narrow-spectrum chemoreceptor cells.