Ultrastructural changes of the microvillar cytoskeleton in the photoreceptor of the crayfish Orconectes limosus related to different adaptation conditions

In the retina of crayfish microvilli of seven of the eight photoreceptor cells build highly organized structures, the rhabdoms. Cytoskeletal elements inside the microvilli were investigated in conventional and slightly extracted electron microscopical preparations. In conventional preparations the ultrastructure of these cytoskeletal elements depended on the adaptational state of the animal. They appeared as central filament-like structures inside each microvillus when dark-adapted retinae were prepared and fixed at night in the absence of calcium. Changes of these conditions (light, daytime, or calcium concentration) impaired the detectability of these central filaments; in light-adapted eyes prepared at midday they were rarely seen. Nevertheless, single microvillar filaments were present in light-adapted retinae after mild cell permeabilization with the saponin beta-escin. They appeared as a regular structure in each microvillus, often attached to the membrane. Their fine structure was consistent with the ultrastructure of single actin filaments as indicated by fast-Fourier-analysis and further supported by the presence of anti-actin immunoreactivity in electron microscopical and immunocytochemical preparations. These results indicate that microvillar filaments are not necessarily destroyed by light as previously described; we suggest that their appearance inside the microvillus might be altered by the properties of associated, maybe sidearm-like proteins.     

Micro-scale fluid and odorant transport to antennules of the crayfish, Procambarus clarkii

A numerical model was developed to determine advective-diffusive transport of odorant molecules to olfactory appendages of the crayfish, Procambarus clarkii. We tested the extent of molecule transport to the surfaces of aesthetasc sensilla during an antennule flick and the degree of odorant exchange during subsequent flicks. During the rapid downstroke of a flick, odorant molecules are advected between adjacent aesthetascs, while during the slower return stroke, these odorants are trapped between the sensilla and molecular diffusion occurs over a sufficient time period to transport odorants to aesthetasc surfaces. During subsequent flicks, up to 97.6?% of these odorants are replaced with new odorant molecules. The concentration of molecules captured along aesthetasc surfaces was found to increase with increased gap spacing between aesthetascs, flick speed, and distance from the proximal end of the aesthetasc, but these changes in morphology and flicking kinematics reduce the animal's ability to take discrete samples of the odorant-laden fluid environment with each flick. Results suggest that antennule flicking allows discrete sampling of the time- and space-varying odorant signal, and high concentration odorant filaments can be distinguished from more diffuse, low concentration filaments through changes in both the timing and the encounter rate of odorant molecules to aesthetasc surfaces.     

The diet of the spiny-cheek crayfish Orconectes limosus in the Czech Republic

The composition of the diet of the invasive spiny-cheek crayfish Orconectes limosus was studied using qualitative and quantitative analyses of stomach contents. A total of 368 specimens collected in 2003–2005 and 2008 in Czech localities were examined, predominantly from the Labe (Elbe) and Vltava River basins. Food components were compared for three size classes of crayfish and both sexes. The following conclusions were reached: (1) the spiny-cheek crayfish is an omnivorous species consuming plants, animals and detritus; (2) quantitatively, the main food component of O. limosus is detritus, while the plant component was second; (3) O. limosus may swallow whole food particles up to 4 mm in size, and the bodies of small animals may sometimes be found undamaged in their stomachs.     

Histological and histochemical observations of the hemolymph cells in the crayfish, Orconectes virilis

Hemolymph cells of Orconectes virilis were stained during the months of August to November by a variety of histological and histochemical techniques. Cells were classified as hyaline cells, small granulocytes, and large granulocytes. Presence of mitochondrial enzymes was indicated by tests for succinic dehydrogenase and cytochrome oxidase. Reaction to test for the hydrolytic enzyme, leucine acylnaphthylamidase was intense in the granules of the large granulocytes. The PAS reaction indicated a mucopolysaccharide at the cell membrane. Lipid was found in all three hemolymph cell types of Orconectes virilis at the time of this study.     

Spiny-cheek crayfish Orconectes limosus carry a novel genotype of the crayfish plague pathogen Aphanomyces astaci

The oomycete Aphanomyces astaci causes mass mortalities of European crayfish. Different species of North American crayfish, original hosts of this parasite, seem to carry different strains of A. astaci. So far, four distinct genotype groups have been recognised using Random Amplification of Polymorphic DNA (RAPD-PCR). We succeeded in isolating A. astaci from the spiny-cheek crayfish Orconectes limosus, a widespread invader in Europe, and confirmed that this species carries a novel A. astaci genotype. Improving knowledge on the diversity of this parasite may facilitate identification of genotypes in mass mortalities of European crayfish, thus tracing the sources of infection.     

The mate pursuit-predation avoidance tradeoff in the virile crayfish, Orconectes virilis

To better understand the tradeoff between mate pursuit and predation risk avoidance, the responses of male virile crayfish (Orconectes virilis) to female sex pheromone and conspecific alarm cue, alone and in combination were tested. Male crayfish were more active and exhibited less antipredator behavior in the pheromone treatment than in either the pheromone + alarm or alarm treatment. The results suggest a tradeoff in favor of risk avoidance when pheromone and risk stimuli are encountered together.     

Some factors regulating cohort production of the crayfish, Orconectes virilis

SUMMARY. Cohort production of the crayfish. Orconectes virilis , ranged from 148.8 to 70.2 kg in North Twin Lake (surface area 1.9 ha) and from 151.9 to 84.9 kg in West Lost Lake (surface area 1.4 ha). Both cohort production (P) and cohort mean biomass (B) showed a long-term decrease with time. The cohort P/B ratios did not show such a trend but remained steady. The P/B ratio approximated the life cycle instantaneous rate of growth (G) which could then be used for estimating cohort production from mean biomass.
Production remained consistently higher in West Lost Lake. Analysis of horizontal life table data revealed no inherent difference between survival and fecundity rates of the crayfish population in each lake. Slight differences in basin morphometry between the two lakes determined nursery habitat availability and this affected recruitment of young from each female brood stock. Small differences in carrying capacity between two similar sized nearby lakes, along with a decrease in carrying capacity over time, were sufficient to nullify attempts to manage these populations using a maximum sustainable yield model.     

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.     

Intercellular junctions of antennal gland epithelial cells in the crayfish,Orconectes virilis

Summary Labyrinth and nephridial canal cells of the crayfish (Orconectes virilis) antennal gland possess two types of intercellular junctions revealed by freeze-fracture studies. Apical margins of the cells are connected by long septate junctions. In replicas, these junctions consist of many parallel rows of 80–140 Å intramembrane particles situated on the PF membrane face (EF and PF fracture faces of Branton et al., 1975). Rows of pits are found on the EF fracture face and are deemed complementary to the rows of particles. Moreover, lateral margins of basal regions of the epithelial cells are attached by many intercellular junctions. These contacts are characterized in thin plastic sections by a narrow dense cytoplasmic plaque located subjacent to the plasma membrane at sites of adjoined cells, and 5 to 12 fine strands of dense material that extend across the intercellular gap between adjoined cells. In freeze-fracture replicas, EF intramembrane faces basal to the region of the plasma membrane containing septate junctions exhibit numerous discoid clusters of particles. The particle aggregates, assumed to represent freeze-cleave images of adhering junctions, range from 900 to 3,700 Å in diameter, with individual particles about 185 Å in diameter. These junctions appear to connect epithelial cell processes formed by basal infoldings of the plasma-lemma, and occur between adjacent cells as well as adjacent processes of a single cell. The discrete aggregates of particles resemble replicated desmosomes (Shienvold and Kelly, 1974) and hemi-desmosomes (Shivers, 1976); therefore, they probably do not constitute a basis for electrical coupling between antennal gland epithelial cells.Supported by the National Research Council of Canada     

Cytochemical observations of hemolymph cells during coagulation in the crayfish, Orconectes virilis

Smears of Orconectes virilis hemolymph were prepared by fixation in 10% formalin immediately upon withdrawal, and after an interval of 1, 5, or 15 minutes. These smears were then stained by a variety of histochemical means designed to identify a material which is released from both hyaline and granular cells during the coagulation process. Based upon reactions to various carbohydrate, lipid and protein tests, this material appears to consist of a glycoor muco-protein, and its localization and activity coincide with the ?fibrin ferment”? described by Hardy (1892). Its release is probably initiated from the hyaline cells, followed shortly thereafter by a similar activity of the granulocytes. While it cannot be ascertained by the methods used in this study whether or not this material participates actively in clotting, its release is nevertheless coincidental with coagulation.     

Exploration of potential microbial control agents for the invasive crayfish,Orconectes virilis

The introduced crayfish, Orconectes virilis (Cambarinae; Hagen 1870), has become a serious invasive species in Arizona (USA), altering stream ecosystems and contributing to the decline of native species. But because it is native to the eastern US, and related crayfish including endangered species inhabit nearby states, introduction of a biological control agent presents a unique challenge. This represents a feasibility study, in which we explored bacteria, nematodes, and a virus as potential biological control agents for O. virilis while avoiding harm to native species. White Spot Syndrome Virus (WSSV) from shrimp was found to be highly pathogenic and readily passed by cannibalistic behavior but not by water transmission. Potential activity of WSSV against representative non-target arthropods that may be found in the same ecosystems was also explored.     

Chemical orientation to food by the crayfish Orconectes rusticus: influence of hydrodynamics

Many different organisms orient to chemicals in a variety of habitats. Each of these habitats has a unique hydrodynamic environment that is dependent upon the structure of that habitat. Differences in the hydrodynamics (i.e. turbulence) of an environment will be reflected in the fine-scale structure of chemical signals. To determine what role dispersion dynamics play in influencing orientation behaviour, we studied crayfish searching for food sources in different artificial streams. Streams differed only in substrate composition (sand or cobbles), and the hydrodynamics associated with different substrates were quantified. A detailed analysis of orientation paths showed that crayfish could orient to food sources in streams with either substrate. The most parsimonious explanation is that animals are using information contained in the spatial and temporal distribution of chemicals in the flow to make directional decisions. Crayfish located the source more quickly, spent more time moving, and walked faster while orienting in streams having a cobble substrate compared with those having a sand substrate. These differences between substrates were not seen in control streams. These results show that the hydrodynamics associated with chemical signal structure can greatly influence the temporal properties of orientation to food sources. For crayfish, differences in the turbulent structure of flow may actually increase orientation efficiency by decreasing search time. On a broader scale, these results show that it is important to quantify orientation behaviour in a number of hydrodynamically different environments. Copyright 1999 The Association for the Study of Animal Behaviour.