Microsporidian Parasites of Trematode Larvae from Aquatic Snails in West Malaysia

In a survey of microsporidian parasites of trematode larvae of Malaysian fresh-water snails, species of Nose-matidae were found 7 times in rediae from 425 Lymnaea rubiginosa, 6 times in rediae from 97 Indoplanorbis exustus and not at all in other snails. There were 3 species of Microsporida in all: one, found in Echinoparyphium dunni, Echinostoma hystricosum and Echinostoma malayanum was identified as Nosema eurytremae Canning; another, which was found in E. dunni and Echinostoma audyi, had paired nuclei (diplokaryon form) in sporogony only and was named a new species, Nosema vasicola sp.n.; the 3rd, from E. hystricosum, lacked diplokaryon nuclei throughout development, was considered to belong to a new genus and was named Unikaryon piriformis gen.n., sp.n. Nosema eurytremae was transmitted experimentally to Fasciola hepatica rediae in Lymnaea truncatula.     

Anisakis pegreffii: a quantitative fluorescence PCR assay for detection in situ

To facilitate improved diagnosis and detection of the third stage larva (L3) of Anisakis pegreffii from the Minnan-Taiwan bank fishing ground in Taiwan Strait, a real-time PCR method for the detection in situ and differentiation was developed to amplify a region of the second internal transcribed spacer (ITS-2) of this parasite. The real-time PCR assay was capable of detecting 1/3 of a single L3 in 30 mg of marine fish tissue, and also exhibited a high level of specificity for A. pegreffii, no fluorescence signals were observed in other five major larval anisakid species found in commercial marine fishes caught in this fishing ground.     

Rapid colonisation of Lymnaea stagnalis by larval trematodes in eutrophic ponds in central Europe

High recruitment rates of multiple species and hierarchical competition are the keys to a competitive exclusion model of community assembly in larval trematode communities in molluscs. Eutrophic environments provide conditions for accelerating trematode transmission and this would increase the strength of interspecific interactions. To test these predictions, we provide the first known assessment for a pulmonate snail host, and for highly productive aquatic environments, of the rates of colonisation and extinction at the level of individual snail host patches, of a large guild of trematode species. Using a uniquely large dataset from a relatively long-term mark-recapture study of Lymnaea stagnalis in six eutrophic fishponds in central Europe, we demonstrate extraordinarily rapid colonisation by trematodes of a snail host, thus meeting the assumptions of the competitive exclusion model. Overall annual colonisation rates ranged from 243% to 503% year⁻¹ so that the odds of trematode establishment in an individual snail in these ponds are two to five times per year. Extinction rates were substantially lower than colonisation rates and, therefore, would not result in turnover rates high enough to significantly affect prevalence patterns in the snail populations. At the species level, analyses of sample-based estimates of probabilities of colonisation revealed that shared species traits associated with transmission and competitive abilities determined the limits of colonisation abilities. Colonisation rates were exceedingly high for the species transmitted to the snails passively via eggs. There was a significant effect of species competitive abilities on colonisation rates due to subordinate species being substantially better colonisers than both strong and weak dominants, a pattern consistent with the predictions of the competition-colonisation trade-off hypothesis. Our results suggest that, with the extraordinarily high trematode colonisation potential in the area studied, the spatial and temporal patterns of intraspecific heterogeneity in recruitment may provide conditions for intensification of interspecific interactions so that complex community assembly rules may be involved.     

Genetic variation in sexual and clonal lineages of a freshwater snail

Sexual reproduction within natural populations of most plants and animals continues to remain an enigma in evolutionary biology. That the enigma persists is not for lack of testable hypotheses but rather because of the lack of suitable study systems in which sexual and asexual females coexist. Here we review our studies on one such organism, the freshwater snail Potamopyrgus antipodarum (Gray). We also present new data that bear on hypotheses for the maintenance of sex and its relationship to clonal diversity. We have found that sexual populations of the snail are composed of diploid females and males, while clonal populations are composed of a high diversity of triploid apomictic females. Sexual and asexual individuals coexist in stable frequencies in many ‘mixed’ populations; genetic data indicate that clones from these mixed populations originated from the local population of sexual individuals without interspecific hybridization. Field data show that clonal and sexual snails have completely overlapping life histories, but individual clonal genotypes are less variable than individuals from the sympatric sexual population. Field data also show segregation of clones among depth‐specific habitat zones within a lake, but clonal diversity remains high even within habitats. A new laboratory experiment revealed extensive clonal variation in reproductive rate, a result which suggests that clonal diversity would be low in nature without some form of frequency‐dependent selection. New results from a long‐term field study of a natural, asexual population reveal that clonal diversity remained nearly constant over a 10‐year period. Nonetheless, clonal turnover occurs, and it occurs in a manner that is consistent with parasite‐mediated, frequency‐dependent selection. Reciprocal cross‐infection experiments have further shown that parasites are more infective to sympatric host snails than to allopatric snails, and that they are also more infective to common clones than rare clones within asexual host populations. Hence we suggest that sexual reproduction in these snails may be maintained, at least in part, by locally adapted parasites. Parasite‐mediated selection possibly also contributes to the maintenance of local clonal diversity within habitats, while clonal selection may be responsible for the distribution of clones among habitats. © 2003 The Linnean Society of London. Biological Journal of the Linnean Society 2003, 79 , 165–181.     

海产双壳类东方肛居吸虫新种及其生活史

本文报告福建沿海菲律宾蛤仔等海产贝类中寄生的东方肛居吸虫Proctoeces orienialis sp.nov.新种及其全程生活史。其第一、第二中间宿主都是海产双壳类,其不结囊的后蚴可在贝类中提早发育,但不象本属其他种类直至孕卵,而需经感染黄鳍鲷才发育成孕卵成虫。各期宿主经人工感染试验研究,发育过程经观察比较。本文还探讨了防护问题。     

Simultaneous quantitative detection of Listeria spp. and Listeria monocytogenes using a duplex real-time PCR-based assay

We report a duplex real-time PCR-based assay for the simultaneous quantitative detection of Listeria spp. and the food-borne pathogen Listeria monocytogenes. The targets of this single tube reaction were the 23S rDNA and hly genes of Listeria spp. and L. monocytogenes, respectively. Our assay was efficient, 100% selective (i.e., it allowed accurate simultaneous identification of 52 L. monocytogenes and 120 Listeria spp. strains through the FAM-labelled hly and the VIC-labelled 23S rDNA probes, respectively); and had a detection limit of one target molecule in 100% (23S rDNA) and 56% (hly) of the reactions. Simultaneous quantification was possible along a 5-log dynamic range, with an upper limit of 30 target molecules and R2 values > 0.995 in both cases. Our results indicate that this assay based on the amplification of the 23S rDNA gene can accurately quantify any mixture of Listeria species and simultaneously unambiguously quantify L. monocytogenes.     

Taxonomy and phylogeny of the xerophilic genus <Emphasis Type="Italic">Wallemia</Emphasis> (Wallemiomycetes and Wallemiales,cl. et ord. nov.)

The genus Wallemia comprises xerophilic species. Based on parenthesome ultrastructure it has been linked to the Filobasidiales (basidiomycetes). Species show a unique type of conidiogenesis, including basauxic development of fertile hyphae, segregation of conidial units more or less basipetally, and disarticulation of conidial units into mostly four arthrospore-like conidia. Wallemia is known from air, soil, dried food (causing spoilage), and salt. It can be isolated from hypersaline water of man-made salterns on different continents. Based on analyses of the nuclear small subunit ribosomal DNA (SSU rDNA) Wallemia has been placed into a highly supported clade together with Ustilaginomycetes and Hymenomycetes (Basidiomycota). Within this clade, it possesses an isolated position distantly related to the Filobasidiales and was characterized by numerous nucleotide substitutions not shared by any other fungus. Tests on xerotolerance indicated that Wallemia presents one of the most xerophilic fungal taxa. Xerotolerance is otherwise rare in the Basidiomycota. To acknowledge its unique morphology, evolution, and xerotolerance, a new basidiomycetous class Wallemiomycetes covering an order Wallemiales, is proposed. Based on differences in conidial size, xerotolerance, and sequence data of the rDNA internal transcribed spacer regions (ITS rDNA), at least three Wallemia species are segregated, identified as Wallemia ichthyophaga, Wallemia sebi, and Torula epizoa var. muriae, for which the combination Wallemia muriae is proposed. The three species are neotypified. Wallemia ichthyophaga differs from W. sebi and W. muriae in numerous nucleotides of the SSU and ITS rDNA. This high variation within Wallemia indicates existence of at least two cryptic genera not distinguishable by morphological characters.     

Parasites on an intertidal Corophium-bed: factors determining the phenology of microphallid trematodes in the intermediate host populations of the mud-snail Hydrobia ulvae and the amphipod Corophium volutator

The phenology of microphallid trematodes within their intermediate hostpopulations has been studied on an intertidal mud flat. The parasites usethe mud snail Hydrobia ulvae and the infaunal amphipod Corophium volutatoras first and secondary intermediate host, respectively. Migratory shorebirdsact as final hosts. Our results show a general trend of decline in thedensity of infected intermediate hosts during both spring and autumn, whichcould mainly be ascribed to shorebird predation. During summer the densityof both infected snails and infected amphipods increased considerably, witha culmination in June within the snail population (1000 infectedm-² and in August within the amphipod population (40 000infected m-². This time lag in parasite occurrence could berelated to (1) the development time of larval trematodes within the snails,(2) higher ambient temperatures in late summer increasing parasitetransmission between snails and amphipods during this period, and (3) ageneral increase in the Corophium population during late summer. Fromsamples collected between 1990 and 1995 it is shown that microphallidtrematodes occasionally may give rise to mass mortality in the amphipodpopulation. The prerequisites for such an event are a high parasiteprevalence within the first intermediate host population and unusually highambient temperatures, facilitating parasite transmission to the secondaryintermediate host, C. volutator.     

Sexual,habitat‐constrained and parasite‐induced dimorphism in the shell of a freshwater mussel (Anodonta anatina,Unionidae)

Intraspecific trends in freshwater mussel (unionoid) shells that are consistently associated with differences in the mussels' sex and/or parasitic infestation can potentially be used to reconstruct sex ratios or parasitic levels of modern and ancient unionoid populations. In contrast to morphological patterns within mammal species, such dimorphic trends within unionoid species are, however, poorly understood. This study investigates, for the first time, to what extent sex, trematode infection and indirect habitat effects determine shell morphology in the freshwater mussel Anodonta anatina. Three of the five study populations displayed significant sexual shell width dimorphism. Here, shells of females were significantly wider than males, probably as a result of altered shell growth to accommodate marsupial gills. In two of these populations, female shells were additionally significantly thinner than those of males, which could be a result of resource depletion by offspring production. Two other A. anatina populations showed no significant dimorphic patterns, and our results indicate that this interpopulational difference in the degree of sexual dimorphism may reflect the overarching effect of habitat on morphology. Thus, populations in the most favourable habitats exhibit faster growth rates, attain larger maximum sizes and produce more offspring, which results in more swollen gills and consequently more inflated shells of gravid females compared to less fecund populations. None of the populations showed any evidence for sexual dimorphism in overall size, growth rate, sagittal shape and density of shells. In addition to sexual dimorphisms, infestation by bucephalid trematode parasites (Rhipidocotyle sp.) significantly altered sagittal and lateral shell shape of A. anatina in one of the populations, with infected specimens growing wider and more elongated. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

长尾蚴吸虫幼虫在菲律宾蛤仔的寄生部位及其组织化学的研究

本文报道长尾蚴吸虫幼虫在菲律宾蛤仔的寄生部位及其组织化学的研究,长尾蚴吸虫幼虫主要寄生于哈仔的生殖腺组织中,仅少部分进入生殖腺附近的消化腺,鳃等。受感染严重的蛤仔,其生殖腺的滤泡等组织被虫体占满并被耗尽,长尾蚴吸虫子胞蚴的胞壁及尾蚴的皮导主要含碱性蛋白质和粘蛋白,子胞蚴的胚球,尾蚴的吸盘,生殖原基,单细胞腺体主要ＤＮＡ阳性物质,排泄囊含丰富的碱性蛋白质;尾蚴体的中部含有呈颗粒团的粘蛋白和抗淀粉酶的