The impact of the crayfish Orconectes virilis on aquatic macrophytes

SUMMARY. 1. The impact of crayfish on the biomass, density and shoot morphology of four submersed plant species was examined under semi-natural conditions. Male or female crayfish ( Orconectes virilis ) were held for 5 weeks at biomasses of 0, 5, 10 or 18 g m⁻² (live weight) in twelve plastic pools (4.67 m², surface area) containing Potamogeton richardsonii, Myriophyllum exalbescens, Nuphar variegatum and Sparganium eurycarpum .
2. Crayfish significantly affected biomass, density and/or shoot morphology of all four macrophyte species. Differences in the effect of crayfish on macrophyte growth were related to plant species, crayfish sex and activity, and the abundance of alternative foods.
3. The effect of female crayfish on macrophyte growth was generally stimulatory. Myriophyllum and Potamogeton biomass, Potamogeton density and Myriophyllum length increased in the presence of female crayfish, possibly due to the reduction in herbivorous snails as a result of crayfish predation. In contrast, plant growth decreased in the presence of male crayfish: Myriophyllum, Nuphar and Potamogeton biomass, Myriophyllum and Sparganium density, and Sparganium and Poiamogeton length were reduced at male crayfish biomasses between 5 and 18 g m⁻².
4. These results indicate that even relatively low densities of crayfish can greatly affect the growth of submersed aquatic plants. Because of their ability to modify aquatic macrophyte, macroinvertebrate and, ultimately, fish communities, the introduction of crayfish into lakes where they do not occur could have a major effect on the structure and composition of the littoral zone.     

Selective foraging by the crayfish Orconectes virilis and its impact on macroinvertebrates

SUMMARY. 1. The impact of crayfish predation on the abundance of macroinvertebrates was examined under semi-natural conditions. Female (Experiment 1) or male (Experiment 2) crayfish (Orconectes virilis) were held for 5 weeks in twelve small pools (4.67 m² surface area) at biomasses of 0. 5, 10 or 18 g m^?2 (live weight). The pools were stocked with known densities of macroinvertebrates. 2. Crayfish significantly affected the abundance of macroinvertebrates in the pools. Differences in the effects of crayfish on macroinvertebrates were related to crayfish sex, the presence of age-0 crayfish, and the species of macroinvertebrate. 3. The abundance of snails (Stagnicola elodes and Physa gyrina) was greatly reduced, in comparison with controls, by biomass of female crayfish ≥10 g m^?2 and by biomasses of male crayfish ≥5 g m^?2. The total density of non-molluscan invertebrates was inversely correlated with the biomass of female crayfish but the total biomass of non-molluscan invertebrates did not differ between treatments. This is consistent with our observation that small invertebrates (<2 mg wet weight) were less numerous, and large amphipods (32–64 mg) were more numerous, in pools stocked with female crayfish. In contrast, male crayfish had little apparent effect on the abundance of non-molluscan invertebrates. 4. Age-0 crayfish hatched at the end of Experiment 1 and were present in each pool at the start of Experiment 2. Surprisingly, male crayfish preyed little on age-0 crayfish. At the end of Experiment 2, the densities of age-0 crayfish varied between six and 116 individuals m^?2 and there was a strong inverse correlation between the mean biomass and density of age-0 crayfish recovered from the pools. This suggests age-0 crayfish were food limited in the pools and may explain the dominance of oligochaetes (which largely escape predation by burrowing) in the invertebrate community at the end of Experiment 2. 5. These results indicate that even relatively low densities of crayfish could greatly affect the abundance of macroinvertebrates in lakes. The introduction of crayfish into lakes (most lakes in Alberta currently have no crayfish) could substantially affect abundance and species composition of the macroinvertebrate community and, ultimately, the fish populations.     

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.     

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.     

The tradeoff between reproductive and food resources in the crayfish Orconectes virilis

The conflict between mating and foraging is one of the many tradeoffs associated with reproduction. The relative attraction to sex pheromone and food stimuli by male virile crayfish (Orconectes virilis) were tested using two experiments. In the first experiment, the responses by males to pheromone and food stimuli alone were assessed. In the second experiment, males were exposed to both pheromone and food stimuli in a choice maze. To determine the effects of feeding motivation, the males in the choice experiment were fed either one day or seven days prior to observation. Male crayfish exhibited similar responses to the pheromone and food stimuli individually. Males exhibited a preference for the pheromone stimulus over the food stimulus in the choice trials, and that preference that was not influenced by starvation.     

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.     

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.     

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.     

Field observations of intraspecific agonistic behavior of two crayfish species,Orconectes rusticus and Orconectes virilis,in different habitats

Agonistic behavior is a fundamental aspect of ecological theories on resource acquisition and sexual selection. Crustaceans are exemplary models for agonistic behavior within the laboratory, but agonistic behavior in natural habitats is often neglected. Laboratory studies do not achieve the same ecological realism as field studies. In an attempt to connect laboratory results to field data and investigate how habitat structure affects agonistic interactions, the nocturnal behavior of two crayfish species was observed by scuba diving and snorkeling in two northern Michigan lakes. Intraspecific agonistic interactions were analyzed in three habitats: two food resources-macrophytes and detritus-and one sheltered habitat. The overall observations reinforce the concept that resources influence agonistic bouts. Fights in the presence of shelters were longer and more intense, suggesting that shelters have a higher perceived value than food resources. Fights in the presence of detritus patches had higher average intensities and ended with more tailflips away from an opponent, suggesting that detritus was a more valuable food resource than macrophytes. In addition, observations of aggressive behavior within a natural setting can add validity to laboratory studies. When fights in nature are compared with laboratory fights, those in nature are shorter, less intense, and less likely to end with a tailflip, but do show the fundamental fight dynamics associated with laboratory studies. Extrinsic and intrinsic factors affect intraspecific aggression in many ways, and both should always be recognized as having the potential to alter agonistic behavior.     

Effects of declining calcium availability on the survival,growth and calcium content of a freshwater crayfish,Orconectes virilis

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Linking phenotypic correlations from a diverse set of laboratory tests to field behaviors in the crayfish,Orconectes virilis

The presence of phenotypic behavioral correlations and their connection to fitness consequences of organisms have received considerable debate within the literature. Yet, little work has been carried out to connect any behavioral correlates found within a set of laboratory studies to natural behavior observed under complex environmental conditions. To help fill this gap, individual crayfish, collected from the same local population, completed five different behavioral assays in a laboratory setting in a random order. These data were used to reveal any possible correlations for behavioral scores across all of the laboratory tests. Subsequently, these same individuals were placed into the field and video recorded for 24 hr. A separate set of field behaviors, related to the laboratory assays, were quantified from the field videos. The normalized laboratory and field behaviors were used in three stepwise statistical analyses. First, normalized data were loaded into a PCA to generate a priori hypotheses on potential behavioral correlates. These hypotheses were subsequently tested using general multiple linear regression. Finally, structural equation modeling was performed to elucidate any behavioral modules from the laboratory assays that correlated with behavioral patterns present from the fieldwork. Three laboratory‐based behavioral modules were connected to three separate field assays: exploration–avoidance, bold–shy, and aggressiveness. Yet, some behaviors exhibited in the laboratory assays were uncorrelated with any behaviors found in the field and vice versa. Results from this study provide evidence that although many different behavioral correlates may exist within laboratory settings, these same modules may not translate directly into predicting behavior under natural settings.     

Isolation and characterization of mitochondrial F(1)-ATPase from crayfish (Orconectes virilis) gills

A soluble F(1)-ATPase was isolated from the mitochondria of crayfish (Orconectes virilis) gill tissue. The maximal mitochondrial disruption rate (95%) was obtained by sonicating for 4 min at pH 8.6. A 15-fold purification was estimated. The properties for both soluble and membrane-bound enzyme were studied. Both enzyme forms were stable at 4 to -70 degrees C when kept in 20% glycerol. Soluble F(1)-ATPase was more stable at room temperature than membrane-bound enzyme. It displayed a narrower pH profile (pK(1) =6.58, pK(2)=7.68) and more acid pH optimum (7.13) than membrane-bound enzyme (pK(1)=6.42, pK(2)=8.55, optimum pH 7.49). The anion-stimulated activities were in the order HCO(3)(-)>SO(4)(2-)>Cl(-). The apparent K(a) values for soluble enzyme were 11.4, 11.2, and 10.9 mM, respectively, but the K(a) of HCO(3)(-) for membrane-bound enzyme (14.9 mM) was higher than for soluble enzyme. Oligomycin and DCCD inhibited membrane-bound F(1)-ATPase with I(50) of 18.6 ng/ml and 2.2 microM, respectively, but were ineffective in inhibiting soluble enzyme. Both enzyme forms shared identical sensitivity to DIDS (I(50)=12.5 microM) and vanadate (I(50)=9.0 mM). Soluble ATPase was significantly more sensitive to pCMB (I(50)=0.15 microM) and NO(3)(-) (I(50)=28.6 mM) than membrane-bound enzyme (I(50)=1.04 microM pCMB and 81.5 mM NO(3)(-)). In addition, soluble F(1)-ATPase was slightly more sensitive to azide (I(50)=91.8 microM) and NBD-Cl (I(50)=9.18 microM) than membrane-bound enzyme (I(50)=111.6 microM azide and 12.88 microM NBD-Cl). These data suggest a conformational change transmission between F(0) and F(1) sectors and slight conformational differences between soluble F(1) and membrane-bound F(1). In addition, an unmodified F(0) stabilizes F(1) and decreases F(1) sensitivities to inhibitors and modulators.