Lactate dehydrogenase in two digenetic trematodes and their host

Polyacrylamide gel electrophoresis of the two digenetic trematodes, Gigantocotyle explanalum from the liver and Gastrothylax crumenifer from the rumen of the water buffalo, Bubalus bubalis revealed the presence of at least six and seven isoenzymes of lactate dehydrogenase (LDH), respectively in a partially purified enzyme preparation. The respective host tissues showed five isoenzymes of LDH, which are characteristic to the vertebrates. Both parachloromercuribenzoate and iodoacetate affected the LDH activity of the parasites and host tissues differently. Spectrophotometric analysis also showed different specific activity and susceptibility to the action of thiol inhibitors. The host LDH was quite stable at 57°C for 30 min, but that of the parasites was less stable.     

Ecosystem consequences of fish parasites*

In most aquatic ecosystems, fishes are hosts to parasites and, sometimes, these parasites can affect fish biology. Some of the most dramatic cases occur when fishes are intermediate hosts for larval parasites. For example, fishes in southern California estuaries are host to many parasites. The most common of these parasites, Euhaplorchis californiensis, infects the brain of the killifish Fundulus parvipinnis and alters its behaviour, making the fish 10–30 times more susceptible to predation by the birds that serve as its definitive host. Parasites like E. californiensis are embedded in food webs because they require trophic transmission. In the Carpinteria Salt Marsh estuarine food web, parasites dominate the links and comprise substantial amount of biomass. Adding parasites to food webs alters important network statistics such as connectance and nestedness. Furthermore, some free‐living stages of parasites are food items for free‐living species. For instance, fishes feed on trematode cercariae. Being embedded in food webs makes parasites sensitive to changes in the environment. In particular, fishing and environmental disturbance, by reducing fish populations, may reduce parasite populations. Indirect evidence suggests a decrease in parasites in commercially fished species over the past three decades. In addition, environmental degradation can affect fish parasites. For these reasons, parasites in fishes may serve as indicators of environmental impacts.     

Life history, ecology and parasite community structure in Soviet birds

The paper describes an investigation of parasite richness in relation to host life history and ecology using data from an extensive survey of helminth parasites (cestodes, trematodes and nematodes) in Soviet birds. Correlates of parasite richness (number of parasite species per host species) were sought among 13 life-history variables, 13 ecological variables and one non-biological variable (number of host individuals examined) across a sample of 158 species of host. A statistical method to control for the effects of phylogenetic association was adopted throughout. Parasite richness correlates positively with the number of hosts examined (sample size) in all three parasite groups. Positive correlations (after controlling for the effects of sample size) were also found between host body weight and parasite richness for trematodes and nematodes, but not for cestodes.
A number of ecological variables were associated with parasite richness. However, when the effects of sample size and body weight were controlled for, only a single significant correlation (an association between trematode richness and aquatic habitat) remained. Similarly, a number of significant correlates of parasite richness were found among the life-history variables examined. Though several of these were robust to the confounding effects of sample size, all could be explained by the co-variation between life-history traits and body weight among the host species under investigation.     

Host diversity and latitude drive trematode diversity patterns in the European freshwater fauna

Aim We investigated the relationship between host and parasite diversity as well as latitudinal gradients in parasite diversity on a continental scale in European freshwater trematodes. Location European freshwaters. Methods We extracted distributional data for 564 freshwater trematodes across 25 biogeographical regions in Europe from the Limnofauna Europaea and used multiple regression analyses to test for correlations between the diversity of definitive (vertebrates) or first intermediate (gastropods) hosts and that of trematodes, and for latitudinal gradients in trematode diversity. In particular, we investigated patterns in beta diversity among latitudinal bands and between trematode species that parasitize host groups with low (autogenic) and high (allogenic) dispersal capacity. We also tested for a latitudinal gradient in the proportional representation of these two trematode groups within regional faunas. Results Latitude or first intermediate host richness had no effect on trematode richness, but definitive host richness was a strong predictor of trematode richness, among both allogenic and autogenic parasites. We found that beta diversity of trematode faunas within latitudinal bands decreased to the north, with similar values for allogenic and autogenic trematodes. Finally, we observed an increasing proportion of autogenic species toward the north of Europe. Main conclusions The richness of definitive hosts appears to be the driver of trematode diversity at a continental scale. The latitudinal gradient in beta diversity reflects patterns observed in free‐living species and probably results from recolonization in the aftermath of the ice ages. The similar beta‐diversity patterns of allogenic and autogenic trematodes and the increasing proportion of autogenic trematodes with increasing latitude are surprising. We suggest that the geographical scale of our analysis or confounding factors such as differences in habitat utilization and specialization may partly explain these patterns.     

Native Parasites Adopt Introduced Bivalves of the North Sea

Introduced species may have a competitive advantage over native species due to a lack of predators or pathogens. In the North Sea region, it has been assumed that no metazoan parasites are to be found in marine introduced species. In an attempt to test this assumption, we found native parasites in the introduced bivalves Crassostrea gigas and Ensis americanus with a prevalence of 35% and 80%, respectively, dominated by the trematode Renicola roscovita. When comparing these introduced species with native bivalves from the same localities, Mytilus edulis and Cerastoderma edule, trematode intensity was always lower in the introduced species. These findings have three major implications: (1) introduced bivalves are not free of detrimental parasites which raises the question whether introduced species have an advantage over native species after invasion, (2) introduced bivalves may divert parasite burdens providing a relief for native species and (3) they may affect parasite populations by influencing the fate of infectious stages, ending either in dead end hosts, not being consumed by potential final hosts or by adding new hosts. Future studies should consider these implications to arrive at a better understanding of the interplay between native parasites and introduced hosts.     

EVIDENCE FOR NEGATIVE FREQUENCY-DEPENDENT SELECTION DURING EXPERIMENTAL COEVOLUTION OF A FRESHWATER SNAIL AND A STERILIZING TREMATODE

Host–parasite coevolution is often suggested as a mechanism for maintaining genetic diversity, but finding direct evidence has proven difficult. In the present study, we examine the process of coevolution using a freshwater New Zealand snail ( Potamopyrgus antipodarum ) and its common parasite (the sterilizing trematode, Microphallus sp.) Specifically, we test for changes in genotypic composition of clonal host populations in experimental populations evolving either with or without parasites for six generations. As predicted under the Red Queen model of coevolution, the initially most common host genotype decreased in frequency in the presence, but not the absence, of parasitism. Furthermore, the initially most common host genotype became more susceptible to infection by the coevolving parasite populations over the course of the experiment. These results are consistent with parasite-meditated selection leading to a rare advantage, and they indicate rapid coevolution at the genotypic level between a host and its parasite.     

福建沿海鱼类吸虫二新种（发状科,隐殖科）

从福建沿海的侧条真鲨的体腔内发现发状科的中国连盘吸虫,新种Anaporrhutum sinicum sp. nov., 虫体大小11.0×4.5mm,卵41—56×18—20μm。这是国内首次报道连盘属吸虫及本科的海水种类。又从福州淡水鱼类鲶鱼的肠道发现隐殖科的叶巢外睾吸虫,新种Exorchis ovariolobularis sp. nov., 虫体大小0.340×0.342mm,卵11—14×7—9μm。     

内蒙科尔沁草原淡水螺吸虫幼虫期的调查研究

本文报道在内蒙科尔沁草原检查5种淡水螺:耳萝卜螺、卵萝卜螺,豆螺、凸旋螺及半球多脉扁螺共5,616粒。从中查出至少12种吸虫幼虫期,它们是:土耳其斯坦东毕吸虫、有棘血居吸虫、马蹄吸虫、斜睾吸虫、二种背孔吸虫、棘口类吸虫、重盘吸虫、球孔吸虫、异形科吸虫、杯叶科吸虫及鹗形吸虫。其中东毕吸虫、血居吸虫及棘口吸虫的尾蚴分别进行实验动物的感染试验,获得成虫。各吸虫侵袭期幼虫季节动态亦经观察。     

Ecdysteroids in helminths and annelids

Summary

This review focuses on recent research developments in the past three years concerning ecdysteroid biochemistry in helminths and annelids, with emphasis on results reported at the IXth Ecdysone Workshop in Paris, France, in September 1989. During the past three years, most of the research in this area has been concentrated on nematodes, in several species of which the occurrence of ecdysteroids has been demonstrated. Interesting biological effects of exogenously applied ecdysteroids have been discovered on meiotic reinitiation in oocytes of the dog heartworm, Dirofilaria immitis, and on microfilarial production by Brugia pahangi. These effects, together with previous discoveries, demonstrate the feasibility of affecting nematode physiology with exogenously applied ecdysteroids. However, experiments with four species of nematodes in three separate laboratories have failed to demonstrate that nematodes biosynthesize ecdysteroids from cholesterol. Therefore, it remains to be proven whether ecdysteroids are truly endogenous nematode hormones or are merely compounds with strong biological activity. Research with cestodes and trematodes has similarly revealed that ecdysteroids occur in these organisms and that the compounds have possible regulatory roles, but experiments demonstrating endogenous biosynthesis have yet to be performed. Annelids, which are more closely related to insects than helminths, also contain ecdysteroids; recent research has demonstrated the C-20 hydroxylation of ecdysone to 20-hydroxyecdysone, the active moulting hormone of most insects. Experiments to demonstrate this metabolic step in helminths have failed.     

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。