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1.
The cause of mollusk decline on the Ogasawara Islands   总被引:2,自引:1,他引:1  
Decline of land snails on the Ogasawara Islands was studied. In Hahajima, major alien predators such as Euglandina rosea and Platydemus manokwari are not present, but some small endemic snails, for example, Hirasea spp. and Ogasawarana spp., are already rare and more common endemic snails, for example, Mandarina spp., are also declining in the northern mountains. The decline cannot be directly explained by forest deforestation and by its subsequent regeneration. Three species of flatworms were found to eat small snails under captive conditions. The distribution of these flatworms is restricted to the northern mountains of Hahajima where Mandarina is declining and its survival is low. These predators are plausible candidates as a cause of the decline of the endemic snails.  相似文献   
2.
The monitoring of gene expression is fundamental for understanding developmental biology. Here we report a successful experimental protocol for in situ hybridization in both whole-mount and sectioned planarian embryos. Conventional in situ hybridization techniques in developmental biology are used on whole-mount preparations. However, given that the inherent lack of external morphological markers in planarian embryos hinders the proper interpretation of gene expression data in whole-mount preparations, here we used sectioned material. We discuss the advantages of sectioned versus whole-mount preparations, namely, better probe penetration, improved tissue preservation, and the possibility to interpret gene expression in relation to internal morphological markers such as the epidermis, the embryonic and definitive pharynges, and the gastrodermis. Optimal fixatives and embedding methods for sectioning are also discussed. A. Cardona and J. Fernández have contributed equally to this work.  相似文献   
3.
Host resistance to parasites and parasite infectivity may be subject to significant genetically determined variation within species. However, relatively little is known of how this variability is structured in natural vertebrate populations and their macroparasites. A laboratory experiment on host susceptibility-parasite infectivity variation in a wildlife host-parasite system (subspecies of the anuran X. laevis and their polystome flatworms), including 33 pairwise allopatric and sympatric host-parasite combinations (three parasite geographical isolates x 11 host full-sibling families, n=600), revealed a complex pattern of infection success. Results amongst host sibships from different localities suggested that infection success was subject to a highly significant locality x parasite isolate interaction. Within localities, a highly significant sibship x isolate interaction also occurred in one of two groups of sibships examined. The existence of such interactions suggests a potential for frequency-dependent, Red Queen-like selection. Interaction between locality and isolate was partly due to higher infection levels in sympatric combinations, consistent with a general pattern of host-specific adaptation. However, some allopatric combinations produced unpredictably high infection levels, resulting in very asymmetrical cross-infectivity patterns (where the reciprocal cross-infections produced negligible infection). This phylogeographically structured host-parasite system may, therefore, sometimes generate local parasite strains with high infectivity to allopatric hosts. Secondary contact between populations could thus result in significant, and unequal, transfer of parasites.  相似文献   
4.
Tissue fluid osmolarity of flatworms kept with moist bark was 243+/-4 S.E.M. mOsm kg(-1). Tissue fluid osmolarity of those kept with water-saturated tissue paper was 205+/-5 S.E.M. mOsm kg(-1). Flatworms placed in water of 300 and 400 mOsm kg(-1) lost weight. Those placed in water of 0, 100 and 200 mOsm kg(-1) gained weight. This suggests that body tissue fluids were approximately 260 mOsm kg(-1). Tissue fluids were slightly hyperosmotic in external media of 200, 300 and 400 mOsm kg(-1), and strongly hyperosmotic at 0 and 100 mOsm kg(-1). The highest measured value of tissue osmolarity was 457 mOsm kg(-1) from a specimen in a medium of 400 mOsm kg(-1). The lowest value was 145 mOsm kg(-1) from a specimen in pure water. Transverse sections of flatworms from different media concentrations suggest that fluids are absorbed into or removed from all tissues.  相似文献   
5.
6.
Ion channels have proved to be productive targets for anthelmintic chemotherapy. One example is the recent discovery of a parasitic flatworm ion channel targeted by praziquantel (PZQ), the main clinical therapy used for treatment of schistosomiasis. The ion channel activated by PZQ – a transient receptor potential ion channel of the melastatin subfamily, named TRPMPZQ – is a Ca2+-permeable ion channel expressed in all parasitic flatworms that are PZQ-sensitive. However, little is currently known about the electrophysiological properties of this target that mediates the deleterious action of PZQ on many trematodes and cestodes. Here, we provide a detailed biophysical characterization of the properties of Schistosoma mansoni TRPMPZQ channel (Sm.TRPMPZQ) in response to PZQ. Single channel electrophysiological analysis demonstrated that Sm.TRPMPZQ when activated by PZQ is a non-selective, large conductance, voltage-insensitive cation channel that displays distinct properties from human TRPM paralogs. Sm.TRPMPZQ is Ca2+-permeable but does not require Ca2+ for channel gating in response to PZQ. TRPMPZQ from Schistosoma japonicum (Sj.TRPMPZQ) and Schistosoma haematobium (Sh.TRPMPZQ) displayed similar characteristics. Profiling Sm.TRPMPZQ responsiveness to PZQ has established a biophysical signature for this channel that will aid future investigation of endogenous TRPMPZQ activity, as well as analyses of endogenous and exogenous regulators of this novel, druggable antiparasitic target.  相似文献   
7.
Summary Synaptic components from the peripheral nervous system of the polyclad flatworm, Notoplana acticola, are described from electron microscopic observations. Quasineuropile, defined as clusters of neurites containing synaptic vesicles, occurs as scattered islands along the peripheral nerve cords of the plexus. Some neurite clusters only contain one type of synaptic vesicle but others are mixed. The most usual synaptic configuration consists of a single presynaptic element and a pair of postsynaptic neurites sharing a common synaptic cleft. These synapses are polarized and contain clear, 420 Å vesicles. GABA-type synapses are also found. At least two kinds of solid-core vesicles also occur.  相似文献   
8.
Ártioposthia triangulata is a terrestrial planarian that feeds on earthworms. Up to 76% of field collected A. triangulata fed on Eisenia fetida earthworms at 10°C in the laboratory. In one experiment, the feeding rate declined from 63% of earthworms attacked to 36% and 34% in the first, second and third feeding opportunities over a week. The average number of E. fetida eaten was 1.4 per planarian per week. The gain in weight of individual A. triangulata was significantly related to the amount of earthworm tissue lost during the feeding process. Over a one week period, the amount of earthworm tissue lost was related to the total amount presented to the planarians but not to their size. Frequency of attack was, however, related to planarian size. The results are discussed in relation to an hypothetical population of earthworms in pasture. It is concluded that the results support the contention that A. triangulata could seriously deplete earthworm populations.  相似文献   
9.
It has been postulated that the high regeneration ability of planarians is supported by totipotent stem cells, called neoblasts. There have been a few reports showing the distribution of neoblasts in planarians. However, the findings were not completely consistent. To determine the distribution of neoblasts, we focused on proliferating cell nuclear antigen (PCNA), which is present in proliferative cells. We cloned and sequenced the cDNA of PCNA from the planarian Dugesia japonica and produced an antiserum recognizing the gene product. X-ray irradiation caused rapid loss of all PCNA-positive cells and loss of the neoblasts (which were morphologically defined by the presence of the chromatoid body), strongly suggesting that all PCNA-positive cells were true neoblasts. Using the antiserum, we were successful in identifying the neoblasts more clearly than any previous work. In addition to their dispersed distribution in the dorsal and ventral mesenchyme, the neoblasts were distributed as clusters along the midline and bilateral lines in the dorsal mesenchyme. We also examined the behavior of the neoblasts after decapitation. Decapitation did not seem to affect the migration of neoblasts far from the wound. We demonstrated here that DjPCNA is a powerful tool for identifying planarian neoblasts.Edited by D.A. Weisblat  相似文献   
10.
Triclad flatworms are well studied for their regenerative properties, yet little is known about their embryonic development. We here describe the embryonic development of the triclad Schmidtea polychroa, using histological and immunocytochemical analysis of whole-mount preparations and sections. During early cleavage (stage 1), yolk cells fuse and enclose the zygote into a syncytium. The zygote divides into blastomeres that dissociate and migrate into the syncytium. During stage 2, a subset of blastomeres differentiate into a transient embryonic epidermis that surrounds the yolk syncytium, and an embryonic pharynx. Other blastomeres divide as a scattered population of cells in the syncytium. During stage 3, the embryonic pharynx imbibes external yolk cells and a gastric cavity is formed in the center of the syncytium. The syncytial yolk and the blastomeres contained within it are compressed into a thin peripheral rind. From a location close to the embryonic pharynx, which defines the posterior pole, bilaterally symmetric ventral nerve cord pioneers extend forward. Stage 4 is characterized by massive proliferation of embryonic cells. Large yolk-filled cells lining the syncytium form the gastrodermis. During stage 5 the external syncytial yolk mantle is resorbed and the embryonic cells contained within differentiate into an irregular scaffold of muscle and nerve cells. Epidermal cells differentiate and replace the transient embryonic epidermis. Through stages 6–8, the embryo adopts its worm-like shape, and loosely scattered populations of differentiating cells consolidate into structurally defined organs. Our analysis reveals a picture of S. polychroa embryogenesis that resembles the morphogenetic events underlying regeneration.Edited by D. Tautz  相似文献   
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