加拿大一枝黄花入侵对土壤动物群落结构的影响

外来植物对入侵地土壤动物群落及理化性质影响的研究不仅有助于评估入侵植物对生态系统的影响,而且对探索外来植物入侵的土壤动物学响应机制尤为重要。为了了解加拿大一枝黄花对入侵地土壤动物的群落结构及理化性质的影响,本文分季节分层次对加拿大一枝黄花不同程度的入侵地进行取样,获得土壤动物9900个,隶属3门11纲14目,弹尾目和蜱螨类均为优势类群。入侵程度不同的样地中土壤动物个体数量和类群组成不同。土壤动物个体数量和类群数量表现为轻度入侵区＞中度入侵区＞重度入侵区;多样性指数和均匀性指数表现为轻度入侵区＜中度入侵区＜重度入侵区,优势度指数表现与前两指数相反。加拿大一枝黄花的入侵没有改变土壤动物表聚性特点。非度量多维标度排序分析表明,不同入侵程度下的土壤动物分为3类,即轻度入侵类、中度入侵类、重度入侵类。不同入侵区域土壤的pH、有机质含量、铵态氮、速效钾和速效磷差异显著(P＜0.05),土壤的含水量和温度差异不显著(P＞0.05)。灰色关联分析表明,入侵区域土壤铵态氮对土壤动物关联最大,有机质含量次之,再次是速效磷和pH,土壤含水量的影响最小。因而,加拿大一枝黄花的入侵,改变了入侵地土壤理化性质(尤其是对铵态氮的调控),进而改变了土壤动物的群落结构,创造了利于自身生长、竞争有利的土壤环境。     

Histopathological response to turpentine in the white shrimp,Penaeus setiferus

Observations are presented on the inflammatory response to a highly irritative substance, turpentine, injected into the abdominal musculature of the white shrimp, Penaeus setiferus. Injections of the irritant were administered with a tuberculin syringe between the fifth and sixth segments. Penaeid shrimp were found to be highly sensitive to turpentine, even when administered in small dosages. When sterile petroleum jelly was mixed with the turpentine to reduce the dispersion rate, the shrimp's “internal defense mechanism” was able to combat effectively the effect of the irritant. Postinjection observations of the tissues at the site of injection, gill, heart, and hepatopancreas were made at 8, 16, 24, 32, 40, 48, 72, 96, 120, 168, and 240 hr, and at 15, 20, 30, 40, 50, 60, and 120 days. The induced cellular inflammatory response consisted of infiltrating hemocytes and fibrocytes resulting in the formation of fibrous capsules, brown melanized nodules, and fibrous scar tissue in all tissues examined. The gills and hepatopancreas showed considerable tissue destruction early, but were eventually cleared of the histopathological effects of the turpentine and later appeared normal. However, extensive tissue destruction was easily distinguishable in the heart and abdominal muscle even at 120 days postinjection.     

The nature of host tissue destruction in tumor invasion. An experimental investigation on carcinoma and sarcoma xenotransplants

The nature of host tissue destruction in tumor invasion was investigated in experimentally induced carcinomas and sarcomas, xenografted into skeletal muscle. By means of light and electron microscopy it was shown that in both carcinomas and sarcomas the confrontation of host tissue with the invading tumor cells does not result in immediate destruction of host tissue but in a transitory state of coexistence which gradually proceeds to progressive host tissue atrophy. This process of progressive atrophy, which finally results in the total disappearance of the invaded host tissue, is considered to be caused mainly by the increasing pressure and competitive withdrawal of oxygen and nutrients by the invading and proliferating tumor cells. Morphological changes suggesting an active enzymatic breakdown of host tissue cells by tumor cells were not observed during any stage of tumor invasion.     

The effect of Heterodera avenae, on the root system of susceptible and resistant oat seedlings

The effects of invasion by the cereal cyst nematode, Heterodera avenae, on the root growth of susceptible and resistant oat seedlings were similar. Nematode invasion directly inhibited root extension and lateral root production, which was dependent upon the developmental status of the invaded root tissue and the nematode density cm-¹ root. Both responses are caused by mechanical damage due to nematode invasion leading to decreased top growth in the host. Reduced root development, decreased efficiency of water and nutrient uptake in invaded plants being indirect effects of nematode invasion.     

An apical protein,Pcr2, is required for persistent movement by the human parasite Toxoplasma gondii

The phylum Apicomplexa includes thousands of species of unicellular parasites that cause a wide range of human and animal diseases such as malaria and toxoplasmosis. To infect, the parasite must first initiate active movement to disseminate through tissue and invade into a host cell, and then cease moving once inside. The parasite moves by gliding on a surface, propelled by an internal cortical actomyosin-based motility apparatus. One of the most effective invaders in Apicomplexa is Toxoplasma gondii, which can infect any nucleated cell and any warm-blooded animal. During invasion, the parasite first makes contact with the host cell "head-on" with the apical complex, which features an elaborate cytoskeletal apparatus and associated structures. Here we report the identification and characterization of a new component of the apical complex, Preconoidal region protein 2 (Pcr2). Pcr2 knockout parasites replicate normally, but they are severely diminished in their capacity for host tissue destruction due to significantly impaired invasion and egress, two vital steps in the lytic cycle. When stimulated for calcium-induced egress, Pcr2 knockout parasites become active, and secrete effectors to lyse the host cell. Calcium-induced secretion of the major adhesin, MIC2, also appears to be normal. However, the movement of the Pcr2 knockout parasite is spasmodic, which drastically compromises egress. In addition to faulty motility, the ability of the Pcr2 knockout parasite to assemble the moving junction is impaired. Both defects likely contribute to the poor efficiency of invasion. Interestingly, actomyosin activity, as indicated by the motion of mEmerald tagged actin chromobody, appears to be largely unperturbed by the loss of Pcr2, raising the possibility that Pcr2 may act downstream of or in parallel with the actomyosin machinery.     

Black spot gill syndrome of the northern shrimp Pandalus borealis

Northern shrimp, Pandalus borealis, taken in the Gulf of Maine show tissue destruction of gill lamellae. Vacuolated chitin growth over damaged tissue produces macroscopic black spots on the gills. First noticed in 1966, semiquantitative records were kept for four consecutive years. Incidence of infestation for this period is described.     

Impact of Oreochromis niloticus (Linnaeus, 1758) (Pisces: Cichlidae) invasion on taxonomic and functional diversity of native fish species in the upper Kabompo River,northwest of Zambia

Invasive alien species have been revealed to drastically alter the structure of native communities; however, there is scarce information on whether taxonomic and functional spaces occupied by native species are equally filled by exotic species. We investigated the diversity of native species to understand the impact of exotic Oreochromis niloticus in the upper Kabompo River, northwest of Zambia using taxonomic and functional diversity indices. To achieve this, two tests were performed (Test 1, compared natives in invaded and uninvaded sections; Test 2, compared natives in invaded section). A total of 17 species were collected for functional diversity computation, out of which fourteen (14) functional trait measurements linked to feeding, locomotion, and life history strategy were taken. Findings revealed that taxonomic and functional diversity values changed with invasion in both tests. Taxonomic diversity was 15% more in invaded than uninvaded sections in Test 1 and was not consistent across sampling points of invaded section in Test 2. Invaded areas were taxonomically less diverse, but functionally diverse in both tests. The analysis of similarity and nonmetric multidimensional scaling revealed no difference in Bray–Curtis similarity assemblages in both tests. Our findings revealed that exotic species more often occupy unfilled gaps in the communities often occupied by the native species; this is achieved by occupying functional spaces. Overall, changes in taxonomic and functional diversity of native species documented here partially confirmed impacts of O. niloticus invasion. Therefore, we recommend a multifaceted approach to assess cumulative impacts of invasion on native species.     

Glutathione enzymes,glutathione content and t-butyl hydroperoxide induced lipid peroxidation in the gill and digestive gland of the estuarine clam,Rangia cuneata

1. Reduced glutathione (GSH), glutathione reductase (GSSG-reductase) and glutathione peroxidase (GSH-peroxidase) activities were measured in the gill and digestive gland of Rangia cuneata.2. Substantial GSH concentrations were found in both gill (820 ± 80 nmole/g tissue) and digestive gland (930 ± 130 nmole/g tissue). The digestive gland exhibited 2.5-fold greater GSSG-reductase activities and 0.5-fold lower GSH-peroxidase activities relative to the gill.3. In vivo exposure to t-butyl hydroperoxide (BHP) elicited a dose-dependent increase (P < 0.05) in lipid peroxidation in both tissues. Lipid peroxidation occurred earlier and to a greater extent in the digestive gland versus the gill. GSH concentrations in both tissues were unaffected by BHP exposure.4. The study results indicate that gill and digestive gland differ in susceptibility to BHP induced oxidative damage, and the difference is accounted for by differences in tissue GSH metabolism.     

The Impact of the Invasive Alien Plant,Impatiens glandulifera,on Pollen Transfer Networks

Biological invasions are a threat to the maintenance of ecological processes, including pollination. Plant-flower visitor networks are traditionally used as a surrogated for pollination at the community level, despite they do not represent the pollination process, which takes place at the stigma of plants where pollen grains are deposited. Here we investigated whether the invasion of the alien plant Impatiens glandulifera (Balsaminaceae) affects pollen transfer at the community level. We asked whether more alien pollen is deposited on the stigmas of plants on invaded sites, whether deposition is affected by stigma type (dry, semidry and wet) and whether the invasion of I. glandulifera changes the structure of the resulting pollen transfer networks. We sampled stigmas of plants on 10 sites invaded by I. glandulifera (hereafter, balsam) and 10 non-invaded control sites. All 20 networks had interactions with balsam pollen, although significantly more balsam pollen was found on plants with dry stigmas in invaded areas. Balsam pollen deposition was restricted to a small subset of plant species, which is surprising because pollinators are known to carry high loads of balsam pollen. Balsam invasion did not affect the loading of native pollen, nor did it affect pollen transfer network properties; networks were modular and poorly nested, both of which are likely to be related to the specificity of pollen transfer interactions. Our results indicate that pollination networks become more specialized when moving from the flower visitation to the level of pollen transfer networks. Therefore, caution is needed when inferring pollination from patterns of insect visitation or insect pollen loads as the relationship between these and pollen deposition is not straightforward.     

Experimental studies on two mutant genes,r and x,in the Mexican axolotl (Ambystoma mexicanum)

Mutant genes r and x, discovered in two unrelated axolotl stocks, are simple recessives determining autonomous cell lethal traits. These traits become recognizable by their characteristic gill and limb patterns which appear in each at about the same period of development. The life spans of the two mutants are approximately the same. Larvae homozygous for both mutants are easily recognized by their smaller size, reduced gill development, and unusually small eyes. None of the three mutant phenotypes (r/r, x/x, rr/xx) is benefited by parabiosis with a normal larva. Transplants of the forelimb area from all three usually were soon invaded by tissues of host origin, resulting in limbs ranging from those almost normal to those reduced to functionless stumps. Those from r/r donors produced the highest percentage of useful limbs. Transplants of the gill-forming area produced gills of the mutant type which, in all cases, regressed. Distention and rupture of gill vessels led to death of some animals. In others the gills became reduced to mere stubs or even disappeared. The failure of replacement of pharyngeal structures of mutant graft origin resulted in the death of all grafted animals from vascular accidents or by prevention of normal feeding or respiration.     

Somatostatin, substance P and calcitonin gene-related peptide-positive intramural nerve structures of the human large intestine affected by carcinoma

The aim of this study was to investigate the arrangement and chemical coding of enteric nerve structures in the human large intestine affected by cancer. Tissue samples comprising all layers of the intestinal wall were collected during surgery form both morphologically unchanged and pathologically altered segments of the intestine (n=15), and fixed by immersion in buffered paraformaldehyde solution. The cryostat sections were processed for double-labelling immunofluorescence to study the distribution of the intramural nerve structures (visualized with antibodies against protein gene-product 9.5) and their chemical coding using antibodies against somatostatin (SOM), substance P (SP) and calcitonin gene-related peptide (CGRP). The microscopic observations revealed distinct morphological differences in the enteric nerve system structure between the region adjacent to the cancer invaded area and the intact part of the intestine. In general, infiltration of the cancer tissue resulted in the gradual (depending on the grade of invasion) first decomposition and reduction to final partial or complete destruction and absence of the neuronal elements. A comparative analysis of immunohistochemically labeled sections (from the unchanged and pathologically altered areas) revealed a statistically significant decrease in the number of CGRP-positive neurons and nerve fibres in both submucous and myenteric plexuses in the transitional zone between morphologically unchanged and cancer-invaded areas. In this zone, a decrease was also observed in the density of SP-positive nerve fibres in all intramural plexuses. Conversely, the investigations demonstrated statistically insignificant differences in number of SP- and SOM-positive neurons and a similar density of SOM-positive nerve fibres in the plexuses of the intact and pathologically changed areas. The differentiation between the potential adaptive changes in ENS or destruction of its elements by cancer invasion should be a subject of further investigations.     

The effect of environmental ammonia concentrations on the ion-exchange of shore crabs,Carcinus maenas (L.)

1. Ion exchange characteristics (ion-permeability, net, passive and active ion fluxes) of adult shore crabs were studied in relation to experimentally-increased external ammonia concentrations.2. Moderately-elevated ammonia concentrations (up to about 1 mmol/1 NH₄⁺) induce an increase in the ion permeability and the salt fluxes across the body wall of Carcinus maenas. At still higher NH₄⁺ concentrations, ion-permeability and ion fluxes are reduced again.3. Active salt influx generally follows the same pattern as observed for whole animal permeability, probably because both parameters are strongly related to gill perfusion and gill ventilation.4. Prolonged exposure to elevated ammonia concentrations in the environment is unfavourable, not because of the NH₄⁺ toxicity, but because of the higher energy requirements associated with the higher salt fluxes.     

The mucous coat on gill lamellae of rainbow trout (Oncorhynchus mykiss)

The existence of a layer of mucus covering the gill lamellae of healthy rainbow trout (Oncorhynchus mykiss) was investigated. Using cryo-scanning electron microscopy, a smooth, undulating, thin layer was observed which completely covered gill filaments and lamellae, thereby obscuring epithelial microridges. After processing cryopreserved gill arches in glutaraldehyde for conventional scanning electron microscopy, the layer was no longer present and epithelial microridges were clearly visible. The identity of this layer was investigated using cryopreserved gills which were treated in one of two ways. First, gills were incubated with a rabbit antiserum to gill mucus, with normal rabbit serum, or with phosphate-buffered saline. Following fixation in glutaraldehyde and processing, only the gill tissue incubated with the mucus-specific antiserum was still covered with the smooth layer. The layer was also retained on the gills of fish anesthetized in a solution containing mucusspecific antiserum and then processes in glutaraldehyde for conventional scanning electron microscopy. The tenacious nature of the mucous layer was demonstrated by its stability following exposure to formalin and a cationic detergent. Second, the presence of this layer was confirmed on gill tissue which was cryopreserved, followed by freeze-substitution and vapor fixation, and then examined by transmission electron microscopy.     

Impacts of Spartina alterniflora invasion on the benthic communities of salt marshes in the Yangtze Estuary,China

As a species for ecological engineering, Spartina alterniflora was introduced to Chongming Dongtan in 1995, and over the last 10 years, this species has rapidly invaded large areas of the Chongming Dongtan nature reserve. In this study, use of a normalized biomass size-spectra (NBSS) approach was explored to evaluate the possible impacts of S. alterniflora invasion on the benthic communities along gradients of intertidal zones and the invasion history of S. alterniflora within the nature reserve. The results showed that the characteristics of macrobenthic communities and the variation in macrobenthic communities described by the first two CCA axes revealed clearly the gradients of elevation and invasion history of S. alterniflora. The differences in the macrobenthic assemblages between the Spartina alterniflara marshes and the native Phragmites australis marshes decreased with increasing of invasion history of S. alterniflara. The macrobenthic biomass showed a decreasing trend, while the meiobenthic biomass showed a reverse trend along the elevation gradient. The macrobenthic biomass of S. alterniflora marshes with longer invasion history was higher than that at recently invaded S. alterniflora marshes, while the meiobenthic biomass was lower. The slopes of NBSS for the sampling sites showed a trend of steeper slopes with decreasing of elevation and at the recently invaded S. alterniflora marshes than that at marshes with longer invasion history, while the differences between the native P. australis marshes and the S. alterniflora marshes with long invasion history tended to be diminished. The NBSS approach could thus be used more widely to detect possible impacts of S. alterniflara invasion on benthic assemblages. This study also indicated the potential for this approach to provide valuable insights into the ecosystem ecology of invasive species, which could be very important for wetland biodiversity conservation and resource management in the Yangtze River Estuary and other such impacted areas.     

The fine structure of the hypertrophont of the parasitic apostome Synophrya (Ciliophora,Apostomatida)

The hypertrophont stage of the parasitic apostome ciliate Synophrya was studied by light microscopy and transmission electron microscopy. This invasive stage of the ciliate was found within the gill lamellae and gill raphes of the longspine swimming crab Portunus spinicarpus. The ciliates elicited a melanized host reaction that walled off the parasite from the host. Additionally the ciliate produced a cyst wall of ～0.16-2.0 μm in thickness that further isolated the parasite. A mouth was not observed, as the internal stage of this ciliate takes in material via endocytosis across the entire surface. The outer surface was irregular, with folds, membrane pillows, and vesicles connected to the outer membrane. The hypertrophont had a sparce ciliature, with well developed kinetodesmal fibers connecting the kinetosomes. Within the cytoplasm the cell had numerous vacuoles, lipid droplets, and large plaquettes of material. The massive reticulate macronucleus had globular and elongated chromatin bodies, and was the most distinctive organelle within the cell.     

Early development and microhabitat of the monogenean Horricauda rhinobatidis, with observations on the related Troglocephalus rhinobatidis, from Rhinobatos batillum from Queensland,Australia

The small monocotylid monogenean Horricauda rhinobatidis is abundant on the gills of its host Rhinobatos batillum, whereas the larger, related monogenean Troglocephalus rhinobatidis is comparatively uncommon. Young specimens of Horricauda live between the host's secondary gill lamellae. Post-oncomiracidia have 14 marginal booklets but as the larvae develop these are supplemented first by a pair of hamuli and then by muscular ventral loculi followed by six forwardly-directed, dorsal spines. By impaling secondary gill lamellae these spines may serve to prevent parasites from being dislodged by gill ventilating currents. Before reaching sexual maturity the parasites leave the secondary gill lamellae and establish themselves in the septal canals. It is uncommon to find more than one adult specimen of Horricauda in each septal canal. The significance of this in relation to sperm exchange is discussed. Like Troglocephalus, Horricauda has eight head sacs, and the suggestion is made that these sacs may play a part in feeding.     

Observations on the phagocytosis and elimination of carmine particles injected into the abdominal musculature of the white shrimp, Penaeus setiferus

White shrimp, Penaeus setiferus, were injected in the abdominal musculature with 0.03 ml of a 1.4% carmine-saline solution and were kept at a temperature of 26°–28°C and a salinity of 23–26‰. Tissue samples were taken at hourly intervals of 1, 6, 12, 18, 24, 30, 36, 42, and 72 hr and at 4, 6, 8, 10, 12, 16, 19, and 33 days post-injection and were examined histologically to determine the sites of phagocytosis and elimination of foreign particulate matter. Within 1 hr post-injection, extracellular clumps of the carmine particles were formed in the hemolymph. These clumps had been invaded by hemocytes at 18 hr, but they persisted throughout the study. Phagocytosis of the particles was accomplished by hemocytes circulating in the hemolymph and by fixed phagocytes in the gill, heart, loose connective tissue, and blood sinusoids in the abdomen. The fate of some phagocytized carmine was climination by the migration of hemocytes through the epithelium of the gills, gut, hepatopancreas, and through the extremities of the pereiopods and the pleopods. Encapsulations or brown nodules were formed in the musculature of the pereiopods around necrotic hemocytes that had phagocytized carmine. A large blister or cyst filled with carmine was formed in the gill cover of one specimen. The obsevation of carmine particles at 33 days post-injection indicates a slow clearance rate of large amounts of abiotic particulate matter in penaeid shrimp.     

Isolation and characterization of symbiotes from the Rocky Mountain wood tick, Dermacentor andersoni

Wolbachia-like symbiotes in the Rocky Mountain wood tick, Dermacentor andersoni, were isolated repeatedly by injection of ovarial tissues into 5-day-old chick embryos. In Giemsa-stained smears of infected embryo tissues, the organisms appeared as blueish or pinkstained coccal bodies indistinguishable from those seen in the ovaries of ticks, where they are located in the luminal epithelium and funicle cells, as well as in oocytes.Electron microscopy revealed that these symbiotes are highly pleomorphic and vary in size from 0.6 to 3.4 μm in diameter. Their fine structure in tissue cells is differentiated into a granular, cortical region, which contains densely stained ribosomes, and a medullary region consisting of a diffuse reticulum partially or completely devoid of granular material or ribosomes. Multiplication is by binary fission. Each organism is delimited by a distinct plasmalemma; a cell wall as in bacterial and rickettsial agents was not observed in organisms from ovarial tissues.Symbiotes cultivated in chick embryos and then injected intracoelomically into adult D. andersoni, developed rapidly and produced massive infestations in hemocytes, hypodermal tissues, salivary glands, and in connective tissues surrounding midgut, Malpighian tubules, and ovary. In hypodermal tissue, organisms with a distinct bilayered cell envelope were occasionally detected. The massive invasion of tissues by injected symbiotes invariably proved fatal for ticks.Results of complement-fixation tests and of fluorescent antibody staining indicated that symbiotes in D. andersoni are closely related to Wolbachia persica, previously isolated from Argas arboreus.     

Cytological Observations of the Infection Process by Phomopsis helianthi (Munt.-Cvet) in Leaves of Sunflower

The infection process of Phomopsis helianthi and the specific degradation of infected tissue were studied in detail using light and transmission electron microscopy. In comparison with other vascular pathogens, the infection and degradation process was in some aspects different. The favourite tissue for the pathogen to grow in was the phloem. Parenchymatic cells in and around vascular bundles were extremely sensitive to infection long before hyphae arrived, probably due to a toxin. In the parenchymatic cells the first changes were visible at the chloroplasts where electron-dense material accumulated in the thylakoid space. The chloroplast stroma changed contrast and later the whole cytoplasm also appeared electron dense. In the vascular bundles, first the phloem was destroyed and then hyphae invaded the adjacent mesophyll, the cambium, and finally the vessel elements. In particular, the compact mesophyll of the midvein was severely affected. Vessel elements were lined with electron-dense material and some were filled with flocculent material. Severe wall destruction indicated the action of a complete set of cell wall-degrading enzymes before hyphae entered the tissue; it always started at the innermost wall layer. Wall degradation in vascular tissue and adjacent parenchyma with intercellular spaces was different. Before the degradation of the protoplasts started, the cell walls were completely metabolized and only the secondary walls of the vessels resisted for longer. There were no host–cell reactions visible that could be interpreted as a defence reaction.