Structure and dynamics of an invasive population of the red swamp crayfish (<Emphasis Type="Italic">Procambarus clarkii</Emphasis>) in a Mediterranean wetland

This study analyzes the population structure and dynamics of an invasive population of Procambarus clarkii (Girard, 1852) in a Mediterranean wetland using the Bhattacharya’s and Von Bertallanfy’s analytical methods. The main purpose was to collect biological data necessary for the management of this nuisance species. A maximum of five age classes were identified for both sexes, three of which being composed of a few or zero individuals. Age classes were classified into two subgroups––spring (SpL) and summer (SuL) lines––on the basis of the different hatching periods. Individuals of SpL showed a faster growth rate and reached a larger body size than those belonging to SuL, probably because they were able to grow for a longer time. No between-sex differences were found in growth patterns except for the asymptotic length (L_∞), which was reached faster by the females. Other population properties were analyzed, such as a high mortality rate, a maximum longevity of 4 years, and a low mean life-time (<12 months). Finally, a relatively small fraction of individuals seemed to survive after the first reproductive peak in spring. Consequently, the structure and dynamics of the study population seem to reveal its stability and spreading potential, as a confirmation of the invasiveness of P. clarkii in Mediterranean wetlands. Handling editor: P. Viaroli     

Cloning and expression of a cDNA encoding a matrix peptide associated with calcification in the exoskeleton of the crayfish

Calcification-associated peptide (CAP)-1 isolated from the exoskeleton of the crayfish, Procambarus clarkii, has anti-calcification activity and chitin-binding ability and is, therefore, considered to be associated with calcification. In this study, a cDNA encoding CAP-1 was cloned and characterized. An open reading frame encoded a pre-propeptide of 99 amino acid residues, which was composed of a signal peptide, a CAP-1 precursor and two-basic amino acid residues at the C-terminus. The dibasic residues were not observed in the natural CAP-1. Expression analyses using Northern blot and RT-PCR revealed that the mRNA encoding CAP-1 was strongly expressed in the epidermal tissue during the postmolt stage, where and when the calcification takes place. These results support that CAP-1 may play an important role in the calcification of the exoskeleton. Based on the nucleotide sequence of the cDNA encoding CAP-1, a recombinant CAP-1 and that carrying the basic residues at the C-terminus were expressed in Escherichia coli. Anti-calcification assay showed that these recombinant peptides were less active than natural CAP-1, indicating that the phosphate group at the 70th residue, Ser, in natural CAP-1 is important for inhibitory activity and that the paired basic residues have some contribution to the elevation of inhibitory activity.     

Synaptic connections between sensory afferents and the common inhibitory motoneuron in crayfish

The sensory inputs to the common inhibitory motoneuron that innervates every leg muscle of the crayfish Procambarus clarkii (Girard) were analyzed by performing intracellular recordings from its neurite within the neuropil of the 5th thoracic ganglion. Two types of sensory inputs involved in locomotion were studied, those from a movement coding proprioceptor (the coxobasal chordotonal organ) and those from sensory neu rons coding contact forces exerted at the tip of the leg on the substrate (the dactyl sensory afferents). Sinusoidal movements applied to the chordotonal organ strand induced a stable biphasic response in the common inhibitory motoneuron that consisted of bursts of spikes during release and stretch of the strand, corresponding to raising and lowering of the leg, respectively. Using ramp movements imposed on the chordotonal strand, we demonstrated that only movement-coding chordotonal afferents produce excitatory post-synaptic potentials in the common inhibitory motoneuron; these connections are monosynaptic. Mechanical or electrical stimulation of the dactyl sensory afferents resulted in an increase in the tonic discharge of the common inhibitory motoneuron through polysynaptic excitatory pathways. These two types of sensory cues reinforce the central command of the common inhibitory motoneuron and contribute to enhancing its activity during leg movements, and thus facilitate the relaxation of tonic muscle fibres during locomotion.Abbreviations ADR anterior distal root - A Lev anterior levator nerve - CB coxo-basipodite joint - CBCO coxo-basal chordotonal organ - CI common inhibitory motoneuron - Dep depressor nerve - DSA dactyl sensory afferents - EPSP excitatory post-synaptic potential - IN interneuron - MN motoneuron - PDR posterior distal root - P Lev posterior levator nerve - Pro promotor nerve - Rem remotor nerve     

Multivesicular body formation and function in the light-adapted crayfish retina: a new interpretation

Summary Quantitative TEM refutes the hypothesis of multivesicular body formation at dawn via the degradation of photoreceptor. No significant relationship exists between multivesicular bodies and rhabdom diameter or between multivesicular bodies and coated vesicles. The density of multivesicular bodies is related to the vesicle-producing Golgi bodies. A new theory concerning the formation and possible function of multivesicular bodies is discussed.     

Breeding biology of the Louisiana red swamp crayfish Procambarus clarkii Girard in Lake Naivasha,Kenya

This paper describes the breeding biology of the Louisiana red swamp crayfish (Procambarus clarkii Girard) that has been introduced in a tropical lake, Naivasha. Notable differences in crayfish biology are found between the place of origin in Louisiana and lake Naivasha.In Naivasha sexual maturity in females is reached at a larger size (42 mm carapace length (CL), 76 mm full length (FL)) than in males (40 mm CL, 71 mm FL). The corresponding figures for Chalmette area of Louisiana are 31–32 mm CL for both sexes and at Ben Hur Research Centre, Louisiana, 33 mm CL. The females weigh between 15 and 20 g at the onset of egg deposition. The corresponding Louisiana values are from 5 to 10 g. Crayfish in Naivasha as in Louisiana breed both inside burrows which are 10–70 cm deep, and on the sediment in shallow water at a depth of between 0.5 and 4 m. These observations suggest that reproduction is very much a lake edge activity. The number of breeding individuals in Naivasha varies with the trend of the water surface level. Sexually active females (form I) as judged from secondary sexual characters (appearance of basal hooks at the base of 3rd and 4th walking legs) persist throughout the year at no less than 60% of the adult male population. This is confirmed by the appearance of recently hatched juveniles (3.4 to 6.5 mm CL) in the water throughout the year. Similarly berried females in Naivasha are found throughout the year, though with peaks at irregular intervals. In Louisiana breeding takes place only from August through November with a single peak in October. The fecundity of crayfish in Naivasha is 433 (SE ± 21, N = 133) and there is a positive correlation between body length and egg number.     

The topological organization of primary afferents in the terminal ganglion of crayfish,Procambarus clarkii

Summary The central projections of primary afferents in the terminal ganglion of the crayfish can be seen when an axonal filling with nickel chloride with subsequent silver intensification was used for identification. We describe here the topological relationships of the projections to the landmark structures of the neuropil.The terminal ganglion has five pairs of sensory nerves associated with the mechanosensory hairs and internal proprioceptors. The projection fields of the primary sensory neurons in the nerves Rl and R2 are almost entirely restricted to the ipsilateral half of the ganglion, whereas those of the nerves R3, R4 and R5 cross the midline to form three sensory commissures, A6SCI, A7SCI and A7SCII. The projection fields are segregated from each other, although all are restricted to the ventral neuropil which lies under the ventral intermediate tract (VIT). The intersegmental projections that ascend via the connective ipsilateral to their origins could be observed. This pattern of projection correlates well with the receptive fields exhibited by several mechanosensory interneurons on the body surface of the final segment.     

Morphology of descending statocyst interneurons in the crayfish Procambarus clarkii Girard

Summary The morphological features of descending interneurons that responded to the artificial bending of statolith hairs were assessed with intracellular recording and staining techniques. Seven statocyst interneurons were identified on the basis of their structure and response characteristics and designated as interneurons S1 to S7. All seven identified interneurons project to the optic lobe, where the optic nerve also projects, and to the dorsal part of the tritocerebrum, where the eyestalk motoneurons originate. All except interneuron S6 also extend their major branches to other neuropilar regions. S2 projects to the dorsal part of the deutocerebrum, where the statocyst nerve terminates, and S3 to the dorsal part of deutocerebrum and the antennal lobe. Four other interneurons (S1, S4, S5, S7) also extend their branches to the parolfactory lobe to which the statocyst nerve projects as well as to the deutocerebrum and antennal lobe. The extensive dendritic projections of S1–S7 suggest that they are complex multimodal interneurons rather than simple relay interneurons, receiving at least visual and statocyst sensory information. The function of the antennal lobe branches, however, has yet to be determined since the functional role of antennal input in equilibrium control is unknown.     

Light-evoked walking in crayfish: Behavioral and neuronal responses triggered by the caudal photoreceptor

The caudal photoreceptors (CPRs) of crayfish (Procambarus clarkii) can trigger walking and abdominal movements by their response to light.

Neuroanatomy of the terminal (sixth abdominal) ganglion of the crayfish,Procambarus clarkii (Girard)

Summary We studied the neuroanatomy of the terminal (sixth abdominal) ganglion in the crayfish Procambarus clarkii with silver-impregnated sections and nickel fills. We describe the fiber tracts, commissures and neuropilar areas, and give the topological relationships of motoneurons and intersegmental interneurons with reference to their neuropilar landmark structures.All five anterior abdominal ganglia have an almost identical number of 600–700 neurons with a similar pattern of distribution. Each contains a single neuromere with a common plan of neuropil organization. In contrast, the terminal ganglion consists of two neuromeres which appear to be derived from the intrinsic sixth abdominal and telson ganglion. The basic organization of each neuromere parallels that of the third abdominal ganglion in the appearance and arrangement of fiber tracts and commissures, although some modifications occur. The fusion of two neuromeres is represented by the duplication of segmentally homologous neurons, MoGs and LGs, whose topological relationships to the neuropil structures are similar to those of the anterior ganglion.We also discuss the origin of the telson and its ganglion (the seventh abdominal neuromere), and dispute the classical theory that the telson derives from a postsegmental region.     

Multimodal responses of the nonspiking giant interneurons in the brain of the crayfish Procambarus clarkii

Three pairs of nonspiking giant interneurons (NGIs; G1, G2, and G3) of the crayfish brain responded with depolarizing and hyperpolarizing graded potentials to body tilt in roll to the ipsi- and contralateral sides in the dark. The higher and the larger the angle of body tilt, the larger was the amplitude of the geotactic responses. In ipsilaterally statocystectomized animals, all the NGIs responded with hyperpolarizing potentials only to the contralateral side-down tilt, whereas in contralaterally statocystectomized animals, they responded with depolarizing potentials only to the ipsilateral side-down tilt. In bilaterally statocystectomized animals, none of the NGIs responded to body tilt in the dark, but in the presence of an overhead light, they exhibited depolarizing and hyperpolarizing potentials in response to body tilt to the ipsi-and contralateral sides, respectively. All the NGIs responded with depolarizing and hyperpolarizing graded potentials to illumination of the contra- and ipsilateral eyes, respectively. The amplitude of these visual responses, however, varied in association with the amplitude of the geotactic response produced by body tilt. These results indicate that the NGIs integrate the sensory inputs from eyes and statocysts and that the interaction between sensory inputs from the left and right sensory organs with either the same modality or with different modalities enhance the directional sensitivity of NGIs as premotoneurons in the compensatory oculomotor system.     

Differences in synaptic output between excitatory and inhibitory motoneurons in a crayfish muscle

A pair of antagonistic motoneurons, one excitatory and one inhibitory, innervates the distal accessory flexor muscle in the walking limb of the crayfish Procambarus clarkii. The number and size of synapses formed by these two axons on the muscle fibers (neuromuscular synapses) and on each other (axo-axonal synapses) were estimated using thin-section electron microscopy. Although profiles of nerve terminals of the two axons occur in roughly equal proportions, the frequency of occurrence of neuromuscular synapses differed markedly: 73% were excitatory and 27% were inhibitory. However, inhibitory synapses were 4–5 times larger than excitatory ones, and consequently, the total contact areas devoted to neuromuscular synapses were similar for both axons. Axo-axonal synapses were predominantly from the inhibitory axon to the excitatory axon (86%), and a few were from the excitatory axon to the inhibitory axon (14%). The role of the inhibitory axo-axonal synapse is presynaptic inhibition, but that of the excitatory axo-axonal synapse is not known. The differences in size of neuromuscular synapses between the two axons may reflect intrinsic determinants of the neuron, while the similarity in total synaptic area may reflect retrograde influences from the muscle for regulating synapse number.     

Taxonomic and size structures of phytophilous macroinvertebrate communities in Vallisneria and Trapa beds of the Hudson River, New York

Phytophilous macroinvertebrates (PMI) were sampled from the surfaces and surrounding water of two aquatic plant species, Vallisneria americana and Trapa natans, which have substantially different morphologies. It was expected that the plants would harbor invertebrate communities of different structure. Total density of PMI was consistently greater in Vallisneria than inTrapa, e.g. 6× greater per m³ water and 21× greater per m² leaf surface in August. Each macrophyte harbored taxa that were either significantly more abundant or present only with that macrophyte; the herbivore Galerucella nymphaceae (Coleptera: Chrysomelidae) was abundant on Trapa. Vallisneria harbored 34 taxa vs. 40 taxa in Trapa, but similarity was low (Morisita's C=0.55–0.66). Predaceous invertebrates were more prevalent in Trapa than in Vallisneria, as were larger individuals. Both PMI communities exhibited shifts in size distribution between July and August. Standing crop of Trapa was 3× greater than forVallisneria. These two macrophyte beds clearly support PMI communities of different taxonomic and size structure, which is believed to be related to the differences in macrophyte morphology.     

Synaptic connections of the common inhibitory motoneurone within the fifth thoracic ganglion of crayfish

The common inhibitor (CI) has been studied morphologically and electrophysiologically in the fifth thoracic ganglion of crayfish (Procambarus clarkii). It has a large soma and possesses two separate dendritic fields arising from distinct integrative segments.In vitro preparations display motor outputs ranging from tonic activity to fictive locomotion. The CI's tonic firing frequency increases as more excitors are recruited, and displays two peaks of frequency during fictive locomotion, one during stance, the other during swing.Paired intracellular recordings have been used to demonstrate the different central synaptic connections received or made by the CI. At least 27% of the proximal excitors receive monosynaptic connections from the CI corresponding to post-synaptic depolarizations of small amplitude mediated by GABA. However as they do not change the overall activities of the excitors which receive them, they may be used for local inhibition within the dendrites. Besides, electrical synapses between several proximal excitors and the CI may synchronize their activity.The CI receives synaptic connections arising from interneurones. Some are direct either by inhibitory monosynaptic connections or by electrical couplings whereas others arise through polysynaptic pathways. All these connections are functionally significant in the control of the CI firing activity and in its motor coordinations.     

Evidence of female cryptic choice in crayfish

To test whether male body size affects female reproductive investment in the polygamous crayfish Procambarus clarkii, we described mating behaviour of virgin females paired with either small or large males, and analysed the number, size and weight of both eggs and juveniles sired by either types of male. Along with confirming the overt selection by females of larger mates, we found that the size and weight of both the eggs and the juveniles were higher when sired by larger fathers. This suggests that P. clarkii females exert a form of cryptic choice for large males, seemingly adjusting the quantity of egg deutoplasm in function of the mate body size. The question of why females spend time and energy to brood low-fitness offspring is finally raised.     

Effects of starvation and - or -alanine administration on the free - and -alanine levels in the muscle and hepatopancreas of the crayfish, Procambarus clarkii

Changes of - and -alanine and other free amino acids were examined in muscle and hepatopancreas of the crayfish Procambarus clarkii before and after a 1-month starvation in freshwater, 50% seawater, and seawater. Total free amino acids and - and -alanine in both tissues decreased during starvation. The largest decrease was found in the animals starved in freshwater. In 50% seawater and full-strength seawater, the ratio of -alanine to total alanine increased in both tissues, although the level was reduced a little. A large dose of -alanine administered into the tail muscle of freshwater crayfish was converted to -alanine and -alanine returned to the control level within a week. A large amount of -alanine was transported from muscle to hepatopancreas. -Alanine injected into freshwater crayfish was converted to -alanine, but was not transported to the hepatopancreas. In the case of -alanine injection into the muscle of crayfish acclimated to 50% seawater, large amounts of - and -alanine were maintained in the muscle during the experimental period of 4 days. These data indicate that -alanine is metabolized actively in crayfish tissues and accumulated as an important osmolyte during osmotic stress.     

Distribution of synapses on two types of ascending interneurons in the crayfish,Procambarus clarkii

Summary About 60 pairs of ascending interneurons are present in the terminal ganglion of the crayfish Procambarus clarkii (Girard). Some of these interneurons have been impaled intracellularly, characterized physiologically, and then labeled with horseradish peroxidase (HRP) to examine the distribution and ultrastructure of synapses. A close relationship between ultrastructure and physiological properties has been found between two types of interneurons, which either have a pre-motor effect upon motor neurons or have no such effect. In one interneuron with a pre-motor effect (6D2), input and output synapses are intermingled on thicker branches, whereas only input synapses are found on small diameter branches. Only input synapses have been observed on the branches in another interneuron with-out a pre-motor effect (6B1). No differences in branch morphology are found in these two interneurons. Interneuron 6D2 contains large numbers of small round agranular vesicles, but the same type of synaptic vesicles is rarely seen in interneuron 6B1, which has no output synapses. Our results indicate a good correlation between the synaptic distribution and pre-motor effects of interneurons in the terminal ganglion.Abbreviations A6, 7 Sixth and seventh abdominal segment of the terminal ganglion - AVC anterior ventral commissure - DC I dorsal commissure I - DIT dorsal intermediate tract - DMT dorsal medial tract - eLG extra lateral giant interneuron - LVT lateral ventral tract - LG lateral giant interneuron - LVT lateral ventral tract - MDT median dorsal tract - MG medial giant interneuron - MoG motor giant neuron - MVT median ventral tract - PVC posterior ventral commissure - R1s sensory fiber tract of nerve root 1 - R3m motor fiber tract of nerve root 3 - R4–7 nerve roots 4–7 - SC I,II sensory commissure I,II - VC I,III ventral commissure I, III - VIT ventral intermediate tract - VLT ventral lateral tract - VMT ventral medial tract     

Colonization of freshwater habitats by an introduced crayfish, <Emphasis Type="Italic">Procambarus clarkii</Emphasis>, in Southwest Iberian Peninsula

The introduction of some crustacean species has produced alterations of freshwater environments and declines of native species worldwide. The red swamp crayfish, Procambarus clarkii Girard, was introduced in the Southwest Iberian Peninsula in the 1970’s, producing severe impacts on rice agriculture and on native biota such as macrophytes, gastropods, native crayfish and amphibians. We studied the distribution of P. clarkii in two areas of SW Iberian Peninsula: the Sado River basin (SW Portugal), an area colonized by this species around 1990, and the Parque Natural del Entorno de Doñana (SW Spain), colonized soon after its introduction in the Iberian Peninsula, in the 1970’s. Our main goal was to determine which factors limit crayfish distribution, which could help to identify the most effective management practices to contain its spread. Procambarus clarkii was found in most types of water bodies, including small and shallow ones. Distance to a crayfish source was the single predictor variable explaining crayfish occurrence in most types of habitats and in both areas. The only exception was for the Sado permanent stream points, where crayfish presence was negatively affected by an interaction between elevation and flow velocity. Other habitat characteristics have apparently little or no importance for its successful colonization. Moreover, this study indicated that overland dispersal is apparently a frequent phenomenon in this species. Our findings can be used to determine which habitats are most likely to be colonized by the crayfish and to develop practical measures which may limit its spread and minimize its impacts.     

Invasion of alien macroalgae in different Mediterranean habitats

The study evaluated different macroalgal invasions in the main Mediterranean coastal habitats on hard bottom. Biodiversity, species composition and structure of macroalgal assemblages were compared among non-invaded areas and areas invaded by the Chlorophyta Caulerpa racemosa var. cylindracea and by the turf-forming Rhodophyta Womersleyella setacea in three different habitats: shallow rocky bottom, deep rocky bottom and dead matte of the seagrass Posidonia oceanica. Results showed that alien macroalgae constituted a relevant component of benthic assemblages in invaded areas of the Mediterranean Sea. Assemblages invaded by Womersleyella setacea and Caulerpa racemosa showed lower values of diversity and large differences in the structure and species composition related to non-nvaded assemblages. The species that mostly suffered from invasion were erect species reproducing sexually; moreover, the dominance of W. setacea led to low abundance of native filamentous algae, while C. racemosa colonization seemed particularly threatening for encrusting algae. All the studied habitats appeared highly invasible by alien macroalgae, even if W. setacea appeared more invasive in deeper habitats, while colonization of C. racemosa seemed more serious in shallower habitats; the dead matte of P. oceanica represented a suitable substrate for the spread of both species. Differences among assemblages in different habitats were reduced in invaded areas.     

Early assessment of the impact of alien species: differential consequences of an invasive crayfish on adult and larval amphibians

Aim Early assessment of the impact of invasive alien species is crucial to set up timely management, but often the impact is evident when it is too late for action. We evaluated relationships between the alien crayfish, Procambarus clarkii, the distribution of native amphibians, and the abundance of their larvae. We assessed whether considering measures of reproductive success provide a more prompt measure of impact than considering just species distribution. Location One hundred and twenty‐five wetlands in Northern Italy, in an area recently invaded by P. clarkii. Methods We surveyed wetlands to assess the presence of breeding activity of amphibians and the distribution of P. clarkii. We measured the abundance of amphibian larvae before metamorphosis through pipe sampling. We built models analysing the relationships between amphibian and crayfish distribution, while taking into account spatial autocorrelation and environmental features. Analyses were performed at both the species level (generalized linear models and spatial eigenvector mapping) and community level (constrained redundancy analysis). Results In terms of breeding site distribution, only two amphibians (Lissotriton vulgaris and Hyla intermedia) were negatively associated with P. clarkii, while the relationships between other the species and P. clarkii were positive or not significant. However, larval abundance for all amphibian species was negatively associated with the alien crayfish. Analyses performed at community and single species levels yielded consistent results. Main conclusions Procambarus clarkii impacts amphibians through different processes. Newts probably avoid invaded wetlands for breeding. Other species attempt breeding in wetlands with crayfish, but suffer very low success. Considering distribution data alone would not provide a correct picture of the impact of this alien species; measures of reproductive success may allow a more accurate assessment of the impact.