Do antennule and aesthetasc structure in the crayfish Orconectes virilis correlate with flow habitat?

The local flow environment affects the shape of waterborne chemical signals through a variety of physical mechanisms and at several scales. Since crayfish rely on these chemical signals to extract information about predators, prey, and mates, one might expect the chemical sensors (aesthetascs) on crayfish antennules to be physically tuned to the presentation of chemical cues by the flow environment. This hypothesis was tested by comparing length, diameter, and spacing of antennules and aesthetascs among geographically distinct populations of Orconectes virilis. Crayfish were collected from the Chagrin river, Hebron hatchery, and Burt lake. In addition, antennules were sampled from 43 museum populations representing 12 lake, 10 creek, and 21 river populations from multiple states and river drainages. Mean velocities from the collection sites were either measured directly or calculated from United States Geological Survey (USGS) historical data. Structural parameters were measured using Scion Image software on Scanning electron microscope micrographs, and analyses of variance were performed using StatView. Structural parameters of aesthetascs were found to vary with flow environment. Aesthetascs from lake populations were inserted at a larger angle, extended out farther from the supporting antennule relative to the width of the antennule, and were more widely spaced than aesthetascs from creek, hatchery, and river populations.     

Development of functional adaptation to clasping behaviour in harpacticoid copepods (Copepoda,Harpacticoida)

The copepodite antennule development of several harpacticoid families is studied and male antennule development of 5 species is schematically illustrated. The origin of newly formed segments can be determined by seta numbers of segments, relative segment length, furrows indicating previous articulations and by the position of the segment which bears the proximal aesthetasc. At least in some species sexual dimorphism of antennules is present from C II onwards. Females practically reach the adult antennular state at C V whereas males undergo drastic changes from C V to C VI with proximal addition of segments, and often with distal fusions and formation of a unique armature due to functional adaptations in clasping behaviour. No correlation has been found between clasping mode, male antennule type and taxonomic level. In closely related species of the same genus both chirocer and subchirocer antennules are found. The postnaupliar development of the chirocer type can proceed along different ways. Consequently it is suggested that at least chirocer antennules have originated several times independently during harpacticoid evolution.     

Antennular sensilla of the brine shrimp, Artemia salina.

1. Scanning electron microscopy was used to characterize the external morphology of setae found on the antennules of adults and nauplii of the brine shrimp, Artemia salina (L.). The permeability of the antennular setae was studied by means of Slifer's crystal violet method. 2. Each antennule of an adult brine shrimp possessed a terminal cluster of sensory setae. Within a cluster there were two morphologically distinct kinds of sensilla, here designated type 1 and type 2. Three type 1 sensilla were observed on every antennule examined. The number of type 2 sensilla per antennule was usually four or five. 3. Type 1 sensilla of adults were 43 to 80 micrometer long and simple in external morphology. They were widest at the base, decreased in diameter gradually, and terminated as a finely tapered tip. No pores were resolved by scanning electron microscopy. 4. Type 2 sensilla of adults were shorter (shaft length, 12 to 23 micrometer) and displayed a single pore at the tip (average pore diameter, 0.4 micrometer). In thin section they were seen to possess a distinctive articular specialization of the cuticle at the base of the seta. 5. Dye penetration experiments indicated that type 2 sensilla were permeable to aqueous crystal violet, whereas type 1 sensilla were not. 6. The antennular setae of nauplii resembled type 1 sensilla in general shape, in being impermeable to crystal violet, and in lacking a terminal pore and basal articular specialization. Moreover, a total of three setae was normally present on each naupliar antennule, and the same number of type 1 sensilla was found on each adult antennule examined. If the three naupliar setae represent a developmental stage in the formation of three adult sensilla, available observations suggest that the larval setae are developmentally related to type 1, rather than to type 2 adult sensilla.     

Morphology and distribution of antennular setae of scyllarid lobsters (Scyllarides aequinoctialis, S. latus, and S. nodifer) with comments on their possible function

Abstract. Lateral flagella of the antennules of scyllarid lobsters were examined for setal morphology and distribution via scanning electron microscopy. Setal distribution patterns were mapped directly for 3 regions of the antennule ( base, tuft , and tip ) and analyzed for differences: (1) between left and right antennules, (2) between males and females within a species, and (3) among species by comparing counts of setae per annulus in the ventral tuft region only. Six types of antennular setae were identified based on their external morphology: aesthetases, simple, modified simple, asymmetric, hemi-plumose, and toothbrush setae. These different types were organized in a clear pattern over the ventral and dorsal surfaces of the lateral flagella of the antennule. Aesthetase, asymmetric, modified simple, and hemi-plumose setae were found only on annuli in the tuft region between the distal and proximal ends of the flagellum. Simple setae were found on all annuli of all regions of the antennule, and toothbrush setae were mainly concentrated on all annuli of the base region and on proximal annuli of the tuft region . All species of scyllarids examined had the same general pattern of setal distribution and no differences were found between left and right, or male and female antennules. Similar setae located on the lateral antennules of species from the families Nephrophidae and Palinuridae (clawed and spiny lobsters) have been previously described as chemo- and/or mechanoreceptive for use in distance chemoreception (i.e., detection and orientation to olfactory stimuli). Based on work on clawed and spiny lobsters, we predict that the aesthetases on slipper lobsters have a chemoreceptive function and that simple and toothbrush setae may have a bimodal chemo- and mechanoreceptive function.     

Predation impact of Leptodora kindtii on population dynamics and morphology of Bosmina fatalis and B. longirostris in mesocosms

1. We assessed the impact of predation by the invertebrate predator Leptodora kindtii on Bosmina longirostris and B. fatalis, which show seasonal and reciprocal succession patterns in Lake Suwa, in a mesocosm experiment using 20‐L tanks with or without the predator under different food conditions. We also analysed morphological responses of the two Bosmina species to the predator in the tanks. 2. Bosmina fatalis dominated B. longirostris regardless of predator presence under high food density. However, the presence of Leptodora induced the dominance of B. fatalis more rapidly than its absence. On the contrary, no dominance of B. fatalis was observed in tanks with low food density, irrespective of the presence of the predator. Only B. fatalis showed morphological changes in response to the presence of Leptodora. 3. Mucrone length and antennule shape (angle between body and antennule and angle between antennules) showed marked responses at both high and low food densities, but antennule length responded only at high food density. Mucrone length seems to be a more effective defence against Leptodora. 4. The results suggest that B. fatalis is a superior competitor against B. longirostris and is more resistant to Leptodora predation, especially in good food conditions. The repeatedly observed seasonal succession of the two Bosmina species in the eutrophic Lake Suwa – the replacement of B. longirostris by B. fatalis following the occurrence of abundant Leptodora– seems to be caused by the selective predation of Leptodora on B. longirostris as well as the competitive ability of B. fatalis.     

Fluid dynamic design of lobster olfactory organs: high speed kinematic analysis of antennule flicking by Panulirus argus

Many organisms use olfactory appendages bearing arrays of microscopic hairs to pick up chemical signals from the surrounding water or air. We report a morphometric and high speed kinematic analysis of the olfactory organs (lateral flagella of the antennules, which bear chemosensory aesthetasc hairs) of the spiny lobster, Panulirus argus. Panulirus argus sample specific locations by executing a rapid series of antennule flicks at one position, moving the antennule to a different spot and then performing another series of flicks. Odorant delivery to an aesthetasc depends on the water motion near it, which depends on its Reynolds number (Re, proportional to both the diameter and speed of the hair). High speed video enabled us to resolve that during a series of flicks, an antennule moves down rapidly (aesthetasc Re = 2) and up more slowly (Re = 0.5), pausing briefly ( approximately 0.54 s) before the next downstroke. The antennules of P. argus operate in a range of Re values and inter-aesthetasc spacings in which penetration of fluid between the hairs in an array is especially sensitive to changes in speed. Therefore, when antennules flick 'old' water is flushed out of the aesthetasc array during the leaky downstroke and is not picked up again during the less leaky upstroke, hence the antennules can take discrete samples. Thus, by operating in this critical Re range these antennules should be particularly effective at sniffing.     

Amputation‐induced activity of progenitor cells leads to rapid regeneration of olfactory tissue in lobsters

Lobsters have a self‐renewing olfactory system and, like many animals, continuously replace old or dying olfactory receptor neurons. In addition, lobsters are able to regenerate the peripheral olfactory system even after complete loss. The olfactory sensors in lobsters are located distally on a pair of antennules. These antennules are often damaged, but this has little impact on the lobster's sense of smell because damaged olfactory tissue is rapidly replaced. In this study, we investigated damage‐induced regeneration of the olfactory system by measuring cell proliferation following controlled amputation. We show that amputation‐induced regeneration occurs as a result of up‐regulating the normal development of olfactory sensors. A unique feature of up‐regulated development is the formation of patches of proliferating cells within the antennular epithelium. Epithelial patches were typically formed between 3 and 10 days postamputation on the amputated side. They were characterized by their: proximal position with respect to developing clusters of olfactory receptor neurons (ORNs); tendency to form two discrete patches within the borders of each existing annulus; cell size, which was approximately twice that of mature ORNs; and location within the ventral epithelium. The development of epithelial patches was immediately followed by proliferation of clusters of ORNs and associated glial cells, and the level of this proliferation increased significantly during the premolt stage of the lobster's molt cycle. These epithelial patches may represent populations of precursor cells, because they develop in response to amputation and immediately precede development of cell clusters composed of ORNs and glia. Possible regulatory signals controlling epithelial patch development are discussed. © 2003 Wiley Periodicals, Inc. J Neurobiol 55: 97–114, 2003     

Amputation-induced activity of progenitor cells leads to rapid regeneration of olfactory tissue in lobsters

Lobsters have a self-renewing olfactory system and, like many animals, continuously replace old or dying olfactory receptor neurons. In addition, lobsters are able to regenerate the peripheral olfactory system even after complete loss. The olfactory sensors in lobsters are located distally on a pair of antennules. These antennules are often damaged, but this has little impact on the lobster's sense of smell because damaged olfactory tissue is rapidly replaced. In this study, we investigated damage-induced regeneration of the olfactory system by measuring cell proliferation following controlled amputation. We show that amputation-induced regeneration occurs as a result of up-regulating the normal development of olfactory sensors. A unique feature of up-regulated development is the formation of patches of proliferating cells within the antennular epithelium. Epithelial patches were typically formed between 3 and 10 days postamputation on the amputated side. They were characterized by their: proximal position with respect to developing clusters of olfactory receptor neurons (ORNs); tendency to form two discrete patches within the borders of each existing annulus; cell size, which was approximately twice that of mature ORNs; and location within the ventral epithelium. The development of epithelial patches was immediately followed by proliferation of clusters of ORNs and associated glial cells, and the level of this proliferation increased significantly during the premolt stage of the lobster's molt cycle. These epithelial patches may represent populations of precursor cells, because they develop in response to amputation and immediately precede development of cell clusters composed of ORNs and glia. Possible regulatory signals controlling epithelial patch development are discussed.     

Molecule capture by olfactory antennules: Mantis shrimp

 A critical step in the process of olfaction is the movement of odorant molecules from the environment to the surface of a chemosensory structure. Many marine crustaceans capture odorant molecules with arrays of chemosensory sensilla (aesthetascs) on antennules that they flick through the water. We developed a model to calculate molecule flux to the surfaces of aesthetascs in order to study how the size, aesthetasc spacing, and flick kinematics of olfactory antennules affect their performance in capturing molecules from the surrounding water. Since the three-dimensional geometry of an aesthetasc-bearing antennule is complex, dynamically-scaled physical models can often provide an efficient method of determining the fluid velocity field through the array. Here we present a method to optimize the incorporation of such measured velocity vector fields into a numerical simulation of the advection and diffusion of odorants to aesthetasc surfaces. Furthermore, unlike earlier models of odorant interception by antennae, our model incorporates odorant concentration distributions that have been measured in turbulent ambient flows. By applying our model to the example of the olfactory antennules of mantis shrimp, we learned that flicking velocity can have profound effects on odorant flux to the aesthetascs if they operate in the speed range in which the leakiness of the gaps between the aesthetascs to fluid movement is sensitive to velocity. This sensitivity creates an asymmetry in molecule fluxes between outstroke and return stroke, which results in an antennule taking discrete samples in space and time, i.e. “sniffing”. As stomatopods grow and their aesthetasc Reynolds number increases, the aesthetasc arrangement on the antennule changes in a way that maintains these asymmetries in leakiness and molecule flux between the outstroke and return stroke, allowing the individual to continue to take discrete samples as it develops. Received: 24 May 2000 / Revised version: 8 May 2001 / Published online: 7 December 2001     

The modality of the dominance signal in snapping shrimp (Alpheus heterochaelis) and the corresponding setal types on the antennules

Previous behavioural experiments showed that snapping shrimp lacking lateral antennular filaments, i.e. without chemosensory aesthetascs, lose the ability to distinguish between conspecifics that are inexperienced in fighting and former winners. A chemosensory dominance signal was assumed to be present, although other receptors unique to the lateral filaments may have been responsible for the behavioural changes. In the present study, the antennules of snapping shrimp were examined for differences between the lateral and medial antennule filaments to identify the modality of the dominance signal. We found six different types of setae and two types of pores. A new probably bimodal setal type is described, the broad long simple seta. Only the chemosensory aesthetascs and their associated hydrosensory companion setae are unique to the lateral filament. Thus we conclude that the dominance signal is chemical, because a hydrodynamic signal would be also received by the simple setae distributed on both filaments.     

Variability of morphological characteristics in <Emphasis Type="Italic">Oithona similis</Emphasis> (Copepoda: Cyclopoida) in the White Sea

The spatial variability of the body size and morphological structures of the planktonic copepod Oithona similis in the White Sea was studied. From north to south, there was a tendency for the male cephalothorax length to decrease. In moving from the central to the northern part of the sea and from the eastern to the western part, the relative antennule length in both sexes increased. The average body size of copepods was positively and the absolute (and relative) lengths of the antennules were negatively correlated with water salinity. The morphological variations have adaptive significance and are determined by environmental factors.     

The modality of the dominance signal in snapping shrimp (Alpheus heterochaelis) and the corresponding setal types on the antennules

Previous behavioural experiments showed that snapping shrimp lacking lateral antennular filaments, i.e. without chemosensory aesthetascs, lose the ability to distinguish between conspecifics that are inexperienced in fighting and former winners. A chemosensory dominance signal was assumed to be present, although other receptors unique to the lateral filaments may have been responsible for the behavioural changes. In the present study, the antennules of snapping shrimp were examined for differences between the lateral and medial antennule filaments to identify the modality of the dominance signal. We found six different types of setae and two types of pores. A new probably bimodal setal type is described, the broad long simple seta. Only the chemosensory aesthetascs and their associated hydrosensory companion setae are unique to the lateral filament. Thus we conclude that the dominance signal is chemical, because a hydrodynamic signal would be also received by the simple setae distributed on both filaments.     

Role of the olfactory pathway in agonistic behavior of crayfish, <Emphasis Type="Italic">Procambarus clarkii</Emphasis>

Crayfish establish social dominance hierarchies through agonistic interactions, and these hierarchies are maintained through assessment of social status. Chemical signals influence several aspects of fighting behavior, but the specific chemosensory sensilla involved in detecting these signals in crayfish are unknown. The goal of our study was to examine the importance of aesthetasc sensilla—olfactory sensors on the antennules of decapod crustaceans—in regulating changes in fighting behavior in crayfish, Procambarus clarkii, over the course of repeated pairings. We selectively ablated aesthetascs from pairs of crayfish after the first day of trials and compared the behavior of these ablated animals to that of pairs of intact controls. Results show that unablated crayfish significantly decreased the number and duration of fights over repeated pairings, whereas crayfish lacking aesthetascs continued to engage in similar amounts of fighting across all three trial days. This difference shows that aesthetascs regulate fighting behavior in P. clarkii.     

Identification of chemosensory sensilla activating antennular grooming behavior in the Caribbean spiny lobster,Panulirus argus

Crustaceans such as crabs and lobsters clean or 'groom' their olfactory organ, the antennule, by wiping it through a pair of mouthpart appendages, the third maxillipeds. In the lobster, only a few chemicals found in prey extracts, especially glutamate, elicit grooming. Chemosensory input driving grooming is likely to be mediated via sensilla located on antennules and third maxillipeds. Chemosensory antennular sensilla are innervated by neurons with central projections either to the glomerular olfactory lobe (aesthetasc sensilla) or to non-glomerular antennular neuropils (nonaesthetasc sensilla). By selectively ablating the chemosensory sensilla on the antennules and the third maxillipeds we have determined that the aesthetascs are necessary and sufficient to drive grooming behavior. Chemosensory activation of antennular grooming behavior likely follows a 'labeled-line' model in that aesthetasc neurons tuned to glutamate provide adequate input via the olfactory lobe to motor centers in the brain controlling antennular movements.     

Biogenic amines stimulate regeneration of cilia in Tetrahymena thermophila

Serotonin and catecholamines affect the regeneration of cilia in Tetrahymena thermophila in a dose-dependent manner: micromolar concentrations are stimulatory, whereas millimolar concentrations have little or no effect. This conclusion is based on motility measurements in regenerating cells and on ciliary counts in scanning electron micrographs. In addition, the recognition mechanism for each hormone appears to be specific and independent. Our results suggest an evolutionary link with hormonal mechanisms in multicellular eukaryotes.     

Heteromorphic antennules protect the olfactory midbrain from atrophy following chronic antennular ablation in freshwater crayfish

Posthatch larval crayfish (Procambarus clarkii) were unilaterally antennulectomized and maintained in the laboratory for a 6-month period, during which time all regenerating antennular stumps were periodically excised. In another group of animals at a similar developmental stage a heteromorphic antennule was induced on the side of the head ipsilateral to the chronically sectioned normal antennule. After 6 months, all experimental animals were sacrificed and their brains were fixed and sectioned. Computer-aided quantitative measurements were obtained for the volumes of the olfactory lobes on both the experimental and control sides of the brains of both groups of crayfish. In the brains of the crayfish group in which only chronic antennualectomy had been performed, the olfactory lobe ipsilateral to the lesion was reduced in volume by about 80% compared to the olfactory lobe on the control side. In animals in which the normal antennule had been chronically ablated, but which possessed a heteromorphic antennule on the same side, the olfactory lobe on the lesioned side differed in volume from the control side by a mean value of only 28%. We conclude that afferent fibers from a heteromorphic antennule ipsilateral to a chronically lesioned normal antennule can assume some of the central trophic functions of the afferents from the normal antennule; thus, the presence of a heteromorphic antennule offers some measure of protection from the dystrophic effects of chronic ablation of the normal antennule during development and growth in crayfish.     

Developmental Patterns and Hypotheses of Homology in the Antennules of Thecostracan Nauplius Larvae (Crustacea)

Abstract Antennular development is summarized for non–brooded nauplius larvae of the Ascothoracida (families Lauridae and Petrarcidae) and for selected nauplii of the Facetotecta. In the Cirripedia Thoracica, nauplii of the Lepadomorpha and Scalpellomorpha/Sessilia are shown to differ in their patterns of antennular setal addition and division into articles, and one or two possible apomorphies for each group are identified. Several variations of the scalpellomorphan/sessilian pattern are outlined. These data on the Ascothoracida, Facetotecta, and Cirripedia provide the basis for modifying an earlier proposal of structural homologies among the naupliar antennules of thecostracan maxillopodans. ‘Virtual’ articles (ones that are never completely free) are invoked to account for setae that ‘jump’ across article boundaries at molts and for supposedly homologous setae found on adjacent articles in different taxa. The identities of the preaxial setae in the Cirripedia are ambiguous and force consideration of two models for that group and for the thecostracan antennular Bauplan; the latter may have included up to 11 or 12 articles, more than the previously supposed 8 or 9. The scoring of characters used in an earlier cladistic study of thecostracan and other maxillopodan taxa is not seriously affected. A comparison with the Cambrian maxillopodan Bredocarissuggests that division of the antennule into discrete articles in extant thecostracans is an apomorphic state and that yet one more apical article once existed in the maxillopodan antennule.     

Cellular origin and ultrastructural changes of regenerating shoots from tobacco (Nicotiana tabacum) internodes cultured in vitro

Ultrastructural changes were studied during shoot formation from tobacco internode slices cultured on Murashige and Skoog's (MS) basal medium plus 0.54 μ M naphthaleneacetic acid, 0.44 μ M 6-benzyladenine, 3% (w/v) sucrose and 0.8% (w/v) agar. Dramatic structural changes were observed in cortical cells below the internodal epidermis, especially those immediately centripetal to the stomata, by light and scanning electron microscopy. Transmission electron microscopic investigation revealed conspicuous structural changes to plastids at each stage during shoot regeneration. To confirm the significance of the cortical cells in shoot regeneration, protoplasts were isolated from them and shoots regenerated successfully. The ability of single cortical cell protoplasts to differentiate into shoots was demonstrated.     

Some Aspects of Regeneration in the Scyphistoma of Cassiopea (Class Scyphozoa) as Revealed by the Use of Antimetabolites and Microspectrophotometry

As a continuation of studies of the regenerative capacitiesof the scyphistoma of Cassiopea, a series of experiments wasundertaken in which (i) regenerating fragments were culturedin the presence of various antimetabolites and (ii) Feulgenstainednuclei from control animals and regenerating fragments weremeasured by scanning, integrating microspectrophotometry. Theresults of the antimetabolite experiments were complex and variablebut nonetheless suggested that normal regeneration of functionalheads from fragments requires the synthesis of DNA, RNA, andprotein. Regardless of the type of antimetabolite, the mostfrequently observed morphological effect was prolonged or arresteddevelopment. None of the antimetabolites produced characteristicor unique abnormalities, although variation was observed inthe ability of the inhibited fragments to recover from the variousantimetabolites. Microspectrophotometric measurements of Feulgen-stainednuclei from control animals revealed that approximately 25%of the nuclei contained more than the diploid amount of DNAand thus were in either the S or G₂ phases of the cell cycle.In regenerating fragments, the frequency of nuclei in this categorydropped progressively to less than 6% by the end of 3 days butreturned nearly to control levels by the end of six days. Thenuclei also became somewhat enlarged and less dense during regeneration.     

Morphology of anterior regeneration in two spionid polychaete species: implications for feeding efficiency

Abstract. In marine soft‐sediment habitats, tissue loss by infuanal invertebrates can provide significant energetic input to higher trophic levels, have substantial impacts on individual behavior, growth, and fecundity, and resulting changes in bioturbation rates can secondarily affect community dynamics. The degree to which a community is affected by such sublethal predation depends in part on whether injured individuals can regenerate and on the speed at which they do so. Previously, we demonstrated differences in the rate of anterior segment and palp regeneration by the spionid polychaetes Pygospio elegans and Dipolydora quadrilobata. The current study examined the morphology of the anterior segment and palp regeneration in these species using scanning electron microscopy (SEM) and indirect immunohistochemistry with confocal laser scanning microscopy at 3, 6, 9, and 12 d post‐ablation. Antibodies for acetylated α‐tubulin and the neural tetrapeptide FMRFamide were used to label the regenerating nervous system. SEM revealed that the morphology of anterior tissue regeneration was similar for both species, but the ciliated food groove tended to form sooner on palps in P. elegans than on those of D. quadrilobata. In both species, palp regeneration and ciliated food groove formation were faster when only palps were removed. A shortened ciliated food groove is likely to reduce particle contact and transport efficiency in suspension and deposit feeding. Regenerating palp nerves were initially visible at 3 d following ablation of palps only, but at 6 d following ablation of five anterior segments. Following ablation of anterior segments, the regenerating nervous system was largely complete by 9 d, nuchal organs were innervated by 6 d, and processes of palp sensory cells were visible at 12 d. Contact chemoreception by sensory cells on the palps may be diminished during the early stages of regeneration, but chemoreception of waterborne cues via the nuchal organ should not.