Diurnal changes in the fine structure of photoreceptors in an abalone,Nordotis discus

Summary The ultrastructure of the synapses in the brain of the monogenean Gastrocotyle trachuri (Platyhelminthes) is described. The synapses consist of one presynaptic terminal separated by a uniformly wide synaptic cleft, from one or more postsynaptic elements. The presynaptic terminals are characterized by the presence of paramembranous dense projections and associated synaptic vesicles. The postsynaptic elements while possessing membrane densities, are usually devoid of vesicles.The structure of the synapses in the brain of Gastrocotyle is compared to synapses from other platyhelminths.     

An in situ hybridization protocol for planarian embryos: monitoring myosin heavy chain gene expression

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.     

Geographic and within-population structure in variable resistance to parasite species and strains in a vertebrate host

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.     

The cause of mollusk decline on the Ogasawara Islands

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.     

The ultrastructure of neuromuscular systems in Notoplana acticola,a free-living polyclad flatworm

Summary Neuromuscular junctions in the marine polyclad flatworm, Notoplana acticola were studied with the electron microscope. Synapses were found between nerve endings and specialized extensions of the muscle cells. Characteristically these processes contained clear cytoplasm with a basal mitochondrion and numerous microtubules aligned parallel to the long axis of the extension. Sarcoplasmic diverticuli which contained the nucleus had granular cytoplasm with an assortment of membranes and organelles. We have proposed the term sarconeural junction to describe synapses between long sarcoplasmic extensions and nerve cells in flatworms as well as other animals.Tight junctions between adjacent contractile portions of muscle cells were common. As groups of cells appeared to be connected by tight junctions or shared common nerve terminals we conjectured that these formed discrete functional motor-units.     

Tissue osmolarity of the New Zealand land flatworm (Arthurdendyus triangulatus)

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.     

Electrophysiological characterization of a schistosome transient receptor potential channel activated by praziquantel

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 TRPM_PZQ – 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 TRPM_PZQ channel (Sm.TRPM_PZQ) in response to PZQ. Single channel electrophysiological analysis demonstrated that Sm.TRPM_PZQ when activated by PZQ is a non-selective, large conductance, voltage-insensitive cation channel that displays distinct properties from human TRPM paralogs. Sm.TRPM_PZQ is Ca²⁺-permeable but does not require Ca²⁺ for channel gating in response to PZQ. TRPM_PZQ from Schistosoma japonicum (Sj.TRPM_PZQ) and Schistosoma haematobium (Sh.TRPM_PZQ) displayed similar characteristics. Profiling Sm.TRPM_PZQ responsiveness to PZQ has established a biophysical signature for this channel that will aid future investigation of endogenous TRPM_PZQ activity, as well as analyses of endogenous and exogenous regulators of this novel, druggable antiparasitic target.     

Fine structural observations on the protonephridium of the terrestrial triclad Geoplana pasipha

Summary The protonephridial system of the terrestrial triclad Geoplana pasipha was studied by electron microscopy. In general construction it conforms to that of the freshwater planarian Dugesia tigrina (McKanna, 1968, 1968 a).Ultrastructural details permit the identification of proximal, collecting, osmoregulatory and nephridiopore regions. Intralumenal material is frequently observed within the tubules, whose cells are always joined by septate junctions. Cilia are numerous and possibly contribute to the flow of water and solutes along the system. Proximal tubules have a peculiar, particulate membrane coat, while a continuous coat, densely stainable with ruthenium red lines the more distal, unciliated tubules.Supported in part by Fundação de Amparo à Pesquisa do Estado de São Paulo and Banco Nacional de Desenvolvimento Econômico     

双雄性交配器官大口涡虫的首次发现

大口涡虫属所有物种均为雌雄同体,具一套交配器官。作者于2015年在广东省的两处淡水环境,首次发现2个具有双雄性交配器官的大口涡虫(Macrostomum sp.)标本。通过对活体、整装片、连续组织切片的显微镜观测,发现2只标本的两套交配器官呈左右排列;每套交配器官具备完整的假储精囊、储精囊、颗粒囊与交配刺;假储精囊与储精囊内具有精子;雄孔分别为1个与2个;交配刺的结构与中国已经记录的物种都不相同。本研究对其做了较为详细的描述,并初步探讨了大口涡虫多交配器官发生的原因。