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Previous studies have demonstrated neuron-specific differences in the inhibitory effects of depolarization upon neurite outgrowth. We examined whether there is a relationship between the normal impulse activity level of an axon and the effect of depolarization upon its growth. Inactive phasic motor axons and active tonic motor axons grow from crayfish abdominal nerve cord explants in culture. Depolarization of these axons with high K+ solutions produced greater inhibition of advancing growth cones from the phasic axons than from the tonic axons. During the period 20–40 min after the beginning of depolarization, tonic axon growth cones continued to advance, whereas phasic axon growth cones retracted. During chronic depolarization, all of the phasic axons retracted during the first day and approximately half of the phasic axons had degenerated after 4 days of depolarization. The majority of tonic axons continue to grow after 3 days of depolarization, and all of the tonic axon growth survived the 4 days of depolarization. The different responses of the growing phasic and tonic axons to depolarization appear to be Ca2+ dependent. The inhibitory effects of depolarization upon phasic axon growth were reduced by the Ca2+ channel blockers La3+ and Mg2+. Application of a Ca2+ ionophore, A23187, produces greater inhibition of phasic axon growth than tonic axon growth. This study demonstrates that depolarization produces greater inhibition of growth from inactive motor axons than from active motor axons. This is likely due to differences in Ca2+ regulation and/or sensitivity to intracellular Ca2+. © 1997 John Wiley & Sons, Inc. J Neurobiol 33: 85–97, 1997 相似文献
184.
Discovery of four natural clones in a crayfish species Procambarus clarkii 总被引:1,自引:0,他引:1
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Yue GH Wang GL Zhu BQ Wang CM Zhu ZY Lo LC 《International journal of biological sciences》2008,4(5):279-282
Self-cloning is quite rare in shrimp, lobsters, crayfish and crabs. Here we report the discovery of four natural clones of red swamp crayfish (Procambarus clarkii), each containing 2-6 genetically identical individuals, during the genotyping of 120 individuals with five microsatellites. The four clones were heterozygote at most of the five microsatellite loci. Phylogenetic analysis using microsatellite genotypes suggests recent origin of the four clones. Sequencing a part of the mitochondrial gene Cox I confirmed that the four clones were from the species Procambarus clarkii. 相似文献
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James Skelton Robert P. Creed Bryan L. Brown 《Proceedings. Biological sciences / The Royal Society》2015,282(1819)
Direct horizontal transmission of pathogenic and mutualistic symbionts has profound consequences for host and symbiont fitness alike. While the importance of contact rates for transmission is widely recognized, the processes that underlie variation in transmission during contact are rarely considered. Here, we took a symbiont''s perspective of transmission as a form of dispersal and adopted the concept of condition-dependent dispersal strategies from the study of free-living organisms to understand and predict variation in transmission in the cleaning symbiosis between crayfish and ectosymbiotic branchiobdellidan worms. Field study showed that symbiont reproductive success was correlated with host size and competition among worms for microhabitats. Laboratory experiments demonstrated high variability in transmission among host contacts. Moreover, symbionts were more likely to disperse when host size and competition for microhabitat created a fitness environment below a discrete minimum threshold. A predictive model based on a condition-dependent symbiont dispersal strategy correctly predicted transmission in 95% of experimental host encounters and the exact magnitude of transmission in 67%, both significantly better than predictions that assumed a fixed transmission rate. Our work provides a dispersal-based understanding of symbiont transmission and suggests adaptive symbiont dispersal strategies can explain variation in transmission dynamics and complex patterns of host infection. 相似文献
187.
Hannu Huuskonen Ari Suhonen Christina Gruber Anssi Vainikka Heikki Hirvonen Raine Kortet 《Marine and Freshwater Behaviour and Physiology》2014,47(3):205-209
Although the temporal consistency of resting metabolic rate in individual animals is generally considered to be a universal phenomenon, studies on invertebrates are still scarce. Here, we studied the repeatability of standard metabolic rate in the signal crayfish (Pacifastacus leniusculus). We measured oxygen consumption twice on the same individuals, on average in 97-day intervals. At intermolt stage, the standard metabolic rate was a repeatable trait. However, molting increased significantly the minimum metabolic rate, thus emphasizing the role of animal physiological state in determining the rate of metabolism. 相似文献
188.
Roberto SACCHI Stefania CANCIAN Daniela GHIA Gianluca FEA Alan COLADONATO 《动物学报(英文版)》2021,67(1):35-43
External coloration in animals depends on the interaction of several different factors including the genetics and epigenetics processes that underlie the color expression,the mechanisms of color perception,and the general mechanisms controlling color evolution and function.Among all,camouflages from predators and conspicuousness are of particular interest because pose animal to choose between opposite adjustment in coloration.The external coloration of crustaceans is mainly due to the accumulation of carotenoids in the exoskeleton and the epidermal layer,and the trade-off between camouflage and communication had led to a variety of responses,involving signal partitioning,spectral sensibility,changing coloration,or signaling behavior.Here,we used digital images to explore intrapopulation variability of the external coloration of Pacifastacus leniusculus among body regions within an individual and between sexes.We found that 1)ventral coloration of claws are more saturated and brilliant than upper parts,2)males express a more saturated and brightness coloration than females,especially on the lower portion of claws,3)color intensity and brightness increases with size differently in different body regions,and 4)brightness is more variable in males than in females.All the above patterns support the hypothesis that color in this species could be the result of a compromise between camouflage from predators and conspicuousness for communication.The results of this study suggest that carotenoid might have something to do with intraspecific communication and perform more complex functions than that of a simple pigment. 相似文献
189.
ANNE SCHRIMPF TORSTEN MAIWALD TRUDE VRLSTAD HOLGER K. SCHULZ PRZEMYSLAW
MIETaNA RALF SCHULZ 《Freshwater Biology》2013,58(6):1116-1125
1. Most European crayfish species are strongly threatened, mainly as a result of the introduced pathogen, Aphanomyces astaci, transmitted by invasive North American crayfish. Long‐term coexistence of American and European crayfish species is therefore regarded as almost impossible, even though some coexisting populations have been observed. 2. In this study, crayfish were collected from presently coexisting populations of the introduced spiny‐cheek crayfish (Orconectes limosus) and the native noble crayfish (Astacus astacus) from nine standing waters in central Europe. Our aim was to resolve whether the coexistence resulted from reduced virulence in local strains of A. astaci, increased immunity in the native crayfish or an absence of the pathogen in these populations. We used highly sensitive A. astaci‐specific real‐time PCR to evaluate the crayfish latent carrier status, combined with transmission experiments to further validate the molecular results. 3. From the total of 523 crayfish tested (490 spiny‐cheek crayfish, 33 noble crayfish), none positive for A. astaci was detected. Transmission experiments confirmed these results: No abnormal mortality or behavioural changes were seen in noble crayfish kept together with American crayfish from the coexisting populations. If we assume a very low prevalence of A. astaci of 10% in a carrier population, there is a 98% probability of disease being absent in five of the nine coexisting populations tested. Hence, a consistent absence, or an extremely low prevalence, of A. astaci seems to allow the coexistence of European and American crayfish in these central European populations. 4. The results are important for native crayfish conservation and management and demonstrate that disease transmission risk may vary substantially between the different populations of spiny‐cheek crayfish in central Europe. 相似文献
190.
1. Crayfish are amongst the most frequently introduced non‐native aquatic organisms, with well‐documented negative effects on a large number of freshwater taxa. Many crayfish‐control strategies make use of manual removal by trapping, a method known preferentially to remove the largest individuals, leaving the juvenile population almost entirely untrapped. 2. Removal by trapping may be used in an attempt to delay colonisation of new stretches by invasive crayfish. It is, however, unclear what effects trapping may have on movement distances of crayfish in wild populations. We examine the impacts of removal by trapping on the movements of American signal crayfish in two UK rivers. 3. We studied four 100 m stretches of two rivers, the Evenlode and Thame, comprising two removal and two non‐removal stretches. Each river supported both treatments. Half of the crayfish captured from the removal sections were removed and humanely destroyed by freezing, and half were marked with their trap location and released there. All crayfish captured from the non‐removal sections were marked and returned at the point of capture. 4. Mean movement distances were smaller in the removal stretches than the non‐removal stretches, both within capture sessions (10.8 and 16.0 m, respectively) and between sessions (14.5 and 24.6 m, respectively), suggesting that removal trapping resulted in the remaining crayfish making smaller movements. Larger crayfish under both treatments made substantially larger movements than those with smaller carapace lengths, both within capture sessions (range 7.6–19.6 m) and between range capture sessions (range 8.9–32.6 m). 5. The results of this study are consistent with expectations if removal by trapping lowered population densities, which we speculate may have affected movement distances directly or indirectly through increasing the availability of food and shelter. 6. This study suggests that trapping at the margins of a population may be sufficient to delay colonisation of new stretches by: (i) maintaining low densities and therefore reducing movements, and (ii) preferentially reducing the population of large individuals, which make the largest movements. However, it remains unlikely that any trapping programme can entirely prevent emigration /dispersal, and therefore colonisation, by signal crayfish. 相似文献