Expression of parasite virulence at different host population densities under natural conditions

It has recently been suggested that the expression of parasite virulence depends on host population density, such that infected hosts have a higher sensitivity to density, and thus reach their carrying capacity earlier than uninfected hosts. In this scenario, parasite-induced reduction in fitness (i.e., virulence) increases with host density. We tested this hypothesis experimentally, using outdoor mesocosm populations of Daphnia magna infected by the microsporidian Octosporea bayeri. Contrary to the prediction, virulence was independent of host density. In a competition experiment with initial prevalence of 50%, O. bayeri reduced the competitive ability of infected Daphnia within the asexual growth phase independent of initial host population density. In an additional experiment we set up populations with 100% and 0% prevalence and followed their population dynamics over the whole season. Consistent with the competition experiment, we found no difference in population dynamics within the asexual growth phase of the host, suggesting that infected hosts are not more sensitive to density than uninfected hosts. The additional experiment, however, included more than the initial growth phase as did the competition experiment. Eventually, after 100 days, 100% infected populations assumed a reduced carrying capacity compared to uninfected populations. We identify and discuss three reasons for the discrepancy between our experiment and the predictions.     

Parasites promote host gene flow in a metapopulation

Local adaptation is a powerful mechanism to maintain genetic diversity in subdivided populations. It counteracts the homogenizing effect of gene flow because immigrants have an inferior fitness in the new habitat. This picture may be reversed in host populations where parasites influence the success of immigrating hosts. Here we report two experiments testing whether parasite abundance and genetic background influences the success of host migration among pools in a Daphnia magna metapopulation. In 22 natural populations of D. magna, immigrant hosts were found to be on average more successful when the resident populations experienced high prevalences of a local microsporidian parasite. We then determined whether this success is due to parasitism per se, or the genetic background of the parasites. In a common garden competition experiment, we found that parasites reduced the fitness of their local hosts relatively more than the fitness of allopatric host genotypes. Our experiments are consistent with theoretical predictions based on coevolutionary host-parasite models in metapopulations. A direct consequence of the observed mechanism is an elevated effective migration rate for the host in the metapopulation.     

The genetics of phototaxis in Daphnia magna: Existence of three phenotypes for vertical migration among parthenogenetic females

Using a cloning technique, we revealed the existence of three phototactically distinct types in Daphnia magna, viz. negatives, positives, and gipsies. The latter migrate continuously between a low and a high light intensity. The expression of this behaviour is genetically determined, although positives and negatives can reversibly switch into gipsies.It is proposed that two opposite genotypes exist, with the gipsy behaviour epigenetically induced. All juveniles behave more or less uniformly, irrespective of their origin. The phototactic responses develop rather late during ontogenesis.     

Daphnia magna as a test animal in acute and chronic toxicity tests

Daphnia magna is a commonly used test animal in aquatic toxicology.Test procedures for acute and chronic test are described, together with the influence of several variables on their results.The practicability of the methods was checked with four model compounds, viz. 1,1,2-trichloroethane, dieldrin, pentachlorophenol and 3,4-dichloroaniline. Toxicity data of these compounds for Daphnia magna are given.     

Mixed infections with Porphyromonas gingivalis and Treponema denticola cause excessive inflammatory responses in a mouse pneumonia model compared with monoinfections

Periodontopathic anaerobes such as Porphyromonas gingivalis are frequently found in aspiration pneumonia and lung abscesses. However, defense mechanisms and responses to these bacterial infections in the lung in vivo remain poorly understood. The coexistence of P. gingivalis with Treponema denticola has been found at higher levels and proportions in periodontally diseased sites. We hypothesized that mixed infections with P. gingivalis and T. denticola can cause severe respiratory disease. In the present study, inflammatory responses to mono- and mixed inoculations with P. gingivalis and T. denticola in the bronchoalveolar lavage (BAL) fluid were investigated. Acute pneumonia and lung abscesses in mice with the mixed infection resulted in a 40% mortality rate within 72 h, compared with only 10% mortality for the respective monoinfections. Pulmonary clearance of P. gingivalis was delayed in the mice with mixed infections with P. gingivalis and T. denticola. Tumor necrosis factor alpha (TNFalpha) interleukin-1beta (IL-1beta) and interleukin-6 (IL-6) levels from BAL fluid of mice with mixed infections at 24 h after inoculation were significantly higher than those after P. gingivalis monoinfection (TNFalpha: P < 0.05, Il-1beta: P < 0.001, IL-6: P < 0.05). The chemokine KC level from BAL fluid of mice at 48 h (P < 0.05) and 72 h after mixed infection was also significantly increased when compared with that after P. gingivalis monoinfection (P < 0.001). The present study demonstrates that a mixed infection of P. gingivalis with T. denticola in mouse causes a marked bronchopneumonia and lung abscess in the mouse model.     

Nutrient removal from sewage by an artificial food web system composed of phytoplankton and Daphnia magna

In order to remove nutrients from sewage, ecotechnology with an artificial food web composed of phytoplankton and Daphnia magna was used. To optimise performance of the system, phytoplankton growth, zooplankton growth, and a continuous-flow system were used. For phytoplankton growth, stirring was 6.7 times faster than the settling in growth rate of Scenedesmus. Zooplankton growth was not influenced by phytoplankton succession, and the specific production coefficient of D. magna was 110.4 mg Daphnia dry weight (DW) per mg chlorophyll a (Chl a). Results indicated that removal of nutrients was better in a long hydraulic residence time (HRT) system than in a system with short HRT. The optimum retention time was found to be 3 days for the phytoplankton chamber and 1.5 days for the subsequent D. magna chamber, respectively, with total retention time of the combined chambers being kept at 4.5 days. When a pilot plant was operated under these conditions, the removal rates of total nitrogen (TN) and total phosphorus (TP) were 68 and 56%, respectively. In the material budget of TN, 32% of inputs passed on to effluent, 39% to sludge, 27% to air and 2% to harvested Daphnia. For TP, 44% of inputs passed on to effluent, 51% to sludge and 4% to Daphnia.     

Automated Recording of Vertical Negative Phototactic Behaviour in Daphnia magna Straus (Crustacea)

Diurnal vertical migration is a well-known phenomenon in the circadian activity rhythms of zooplankton. Our goal was to test whether negative phototaxis in Daphnia magna clone BEAK (provoked by artificially induced light stress, alternating light and dark phases in 2 h intervals), and its interference with the endogenous rhythm of diurnal vertical migration, can be automatically registered with a biomonitor. For the first time the vertical swimming behaviour of D. magna was recorded quantitatively based on non-optical data recording in a fully automated biotest system, the Multispecies Freshwater Biomonitor in a new experimental setup consisting of a column of three recording units (3-level chambers). Circadian vertical migration was clearly recorded in the 3-level chambers and the rhythm was more clear with 5 than with 1 organism per chamber. The organisms clearly responded to induced light stress with negative phototaxis, however best in larger chambers. The artificially induced rhythm was influenced by the endogenous rhythm. This approach may facilitate long-term observations of vertical swimming activity of zooplankton in the future.     

Resistance to a bacterial parasite in the crustacean Daphnia magna shows Mendelian segregation with dominance

The influence of host and parasite genetic background on infection outcome is a topic of great interest because of its pertinence to theoretical issues in evolutionary biology. In the present study, we use a classical genetics approach to examine the mode of inheritance of infection outcome in the crustacean Daphnia magna when exposed to the bacterial parasite Pasteuria ramosa. In contrast to previous studies in this system, we use a clone of P. ramosa, not field isolates, which allows for a more definitive interpretation of results. We test parental, F1, F2, backcross and selfed parental clones (total 284 genotypes) for susceptibility against a clone of P. ramosa using two different methods, infection trials and the recently developed attachment test. We find that D. magna clones reliably exhibit either complete resistance or complete susceptibility to P. ramosa clone C1 and that resistance is dominant, and inherited in a pattern consistent with Mendelian segregation of a single-locus with two alleles. The finding of a single host locus controlling susceptibility to P. ramosa suggests that the previously observed genotype-genotype interactions in this system have a simple genetic basis. This has important implications for the outcome of host-parasite co-evolution. Our results add to the growing body of evidence that resistance to parasites in invertebrates is mostly coded by one or few loci with dominance.     

Prevalence of coccidia parasites (Protozoa) in red squirrels ( Sciurus vulgaris): effects of host phenotype and environmental factors

We investigated the relative importance of environmental factors versus host phenotype in determining parasite prevalence in Eurasian red squirrels ( Sciurus vulgaris). One hundred and forty-three fecal samples of 116 different squirrels collected in 2000 and 2001 from five study areas in the Italian Alps, were examined for intestinal protozoans. Two species of Eimeria were present with a medium to high prevalence in both years and in all areas, while two other species were rare, occurring only in some areas and not in all years. Cryptosporidium parvum had a high prevalence in the two study areas of the Western Alps, while in the three areas of the Central Alps it was recorded only once. The prevalence of Eimeria sciurorum and C. parvum fluctuated in parallel with squirrel density, suggesting a possible correlation between the presence of these protozoans and host density. A gender effect on E. sciurorum prevalence at low density could be explained by different space use patterns and social organization of males and females. C. parvum occurred more frequently in young squirrels, suggesting an acquired immunity in adults, but age-related susceptibility was not found for eimerian species. The coccidian community was more similar within than between regions, and study area and year were key parameters in predicting coccidia infection. There was no evidence of competition between coccidian species, but one positive interaction between E. sciurorum and E. andrewsi was observed. Our results suggest that the effects of geographic region, area features, and year effects probably related to fluctuations in host population density, were more important than individual phenotypic host characteristics in structuring the coccidian assemblage and determining levels of parasite prevalence in red squirrel populations.     

Top-down control of natural phyto- and bacterioplankton prey communities by Daphnia magna and by the natural zooplankton community of the hypertrophic Lake Blankaart

Biomanipulation, through the reduction of fish abundance resulting in an increase of large filter feeders and a stronger top-down control on algae, is commonly used as a lake restoration tool in eutrophic lakes. However, cyanobacteria, often found in eutrophic ponds, can influence the grazing capacity of filter feeding zooplankton. We performed grazing experiments in hypertrophic Lake Blankaart during two consecutive summers (1998, with and 1999, without cyanobacteria) to elucidate the influence of cyanobacteria on the grazing pressure of zooplankton communities. We compared the grazing pressure of the natural macrozooplankton community (mainly small to medium-sized cladocerans and copepods) with that of large Daphnia magna on the natural bacterioplankton and phytoplankton prey communities. Our results showed that in the absence of cyanobacteria, Daphnia magna grazing pressure on bacteria was higher compared to the grazing pressure of the natural zooplankton community. However, Daphnia grazing rates on phytoplankton were not significantly different compared to the grazing rates of the natural zooplankton community. When cyanobacteria were abundant, grazing pressure of Daphnia magnaseemed to be inhibited, and the grazing pressure on bacteria and phytoplankton was similar to that of the natural macrozooplankton community. Our results suggest that biomanipulation may not always result in a more effective top-down control of the algal biomass.     

红霉素对大型溞生殖、生长和基因表达的生态毒理效应

红霉素（ERM）在水环境中广泛检出,并产生生态毒理风险。以大型溞为模式生物,研究了ERM在浮游动物繁殖、生长、抗氧化及神经系统方面的慢性毒理效应。结果表明ERM对大型溞的急性毒性为低毒（48 h-LC₅₀为315.41 mg/L,96 h-LC₅₀为163.08 mg/L）。在2 μg/L和200 μg/L浓度下暴露21 d,ERM会干扰大型溞的繁殖、生长、氧化应激防御及解毒相关基因的表达,诱导丙二醛含量上升,抑制抗氧化系统超氧化物歧化酶和谷胱甘肽转移酶及神经系统乙酰胆碱酯酶活性,引起细胞膜损伤和神经传导紊乱,造成大型溞前期产卵率升高,且对生长发育和游泳行为产生不利影响。解析了ERM在浮游动物繁殖、生长及在蛋白和基因水平上的毒理响应,为揭示抗生素对水生生物种群稳定和生态系统安全的影响提供基础数据支撑。     

<Emphasis Type="Italic">Daphnia</Emphasis>species diversity in Kenya,and a key to the identification of their ephippia

The distribution of Daphniaspecies in tropical Africa is poorly known and understood. Daphniaare assumed rare in tropical regions, but systematic studies covering large areas are sparse. We sampled the active community (live zooplankton) and/or the dormant community (diapausing egg banks in the sediment) of 41 standing water bodies in Kenya in search for Daphnia.Overall the dormant communities yielded 11 species of Daphnia, a species richness more than twice the species richness found in the active communities. Dormant community species diversity better reflects the spatial, and particularly the temporal (multi-annual) variation in environmental conditions available to Daphniain these tropical standing waters. Hence, we suggest that the dormant community be taken into account when assessing local zooplankton diversity, especially in fluctuating tropical lake ecosystems, where the presence of each local Daphniaspecies in the active community may be strongly seasonal or erratic. Geographic distribution data from this study are supplemented with previous records of Daphniain East Africa to provide an overview of the known distribution of Daphniain Kenya and neighbouring countries. We also present a detailed key for morphological identification of the ephippia of the 11 Daphniaspecies encountered, complemented with photographs and drawings of diagnostic characters.     

Treatment at different depths and vertical mixing within a 1-m deep horizontal subsurface-flow wetland

The aim of this study was to examine the variation in treatment performance at three depths, and the degree of vertical mixing, within a 1.0 m deep horizontal subsurface-flow constructed wetland (HSSF-CW) planted with Schoenoplectus tabernaemontani (Gmel.) Palla, and treating primary settled municipal wastewater in sub-tropical New South Wales, Australia. Water samples were collected from the upper (0.17 m), middle (0.5 m), and lower (0.83 m) depths at five equi-spaced sample points along the longitudinal axis of the 8.8 m² bed during two trials. Analysis of covariance (ANCOVA) indicated that the rate of pollutant concentration reduction between the three depths was not significantly different (p > 0.05) for all of the measured parameters (dissolved oxygen (DO), hydrogen electrode potentials (E_h), 5-day biochemical oxygen demand (BOD₅)) total nitrogen (TN), TKN, and NH₄-N. Thus, it can be concluded that the break-down of contaminants as wastewater moved through the HSSF-CW was approximately uniform across the 1.0 m depth profile. The lack of a significant depth effect can be largely explained by the substantial amount of vertical mixing that was observed when a pulse of lithium tracer was injected into the middle depth of the first intermediate sampling point. The tracer rapidly migrated vertically into the upper and lower depths as water moved through the bed and was almost completely mixed between the three depths by the time it reached the last intermediate sampling point.The majority of BOD₅ removal occurred within the first-third of the bed where vegetation cover was poor. Performance of the bed declined over time from Trial 1 to Trial 2, possibly due to a cumulative build-up of organic matter within the substrate as a result of limited oxygen transfer throughout the 1.0 m depth of substrate via root leakage or diffusion across the air–water interface. Root penetration was limited to the upper 0.4 m of the substrate, with the majority of below-ground biomass forming a dense mat in the upper 0.2 m. A comparison of two-parameter (K–C^*) first-order volumetric rate constant (K_v20) with those obtained from 0.4 to 0.6 m deep HSSF-CW in the same region indicate that a doubling of the wetted depth resulted in no improvement in BOD₅ removal and a decline in TN removal on an areal basis. Further investigations are warranted, comparing the performance of replicated beds spanning a range of depths (e.g. 0.25, 0.5 and 1.0 m) in order to quantitatively determine the optimal depth of HSSF-CWs treating domestic wastewater.     

Shoaling behaviour of sticklebacks infected with the microsporidian parasite, <Emphasis Type="Italic">Glugea anomala</Emphasis>

We compared the shoaling behaviour of three-spined sticklebacks, Gasterosteus aculeatus, infected with the microsporidian, Glugea anomala, to that of non-infected conspecifics. Infected fish lost significantly more weight than non-infected fish during a period of food deprivation, suggesting a metabolic cost to parasitism. In binary shoal choice tests, non-infected test fish showed an association preference for a shoal of non-infected over a shoal of infected conspecifics; infected test fish displayed no preference. Infected fish, however, showed a higher overall tendency to shoal than non-parasitised fish. Furthermore, infected fish occupied front positions within a mixed school. We consider the behavioural differences between infected and uninfected fish in the context of their potential benefits to the fish hosts and the parasites.     

Colonization of Sitka spruce stumps by decay-causing hymenomycetes in paired inoculations

Sitka spruce stumps were inoculated with decay fungi using colonized sawdust or dowel inoculum to investigate colonization in paired combinations. Estimates of domain sizes were made in the top 15 cm of stump after 13–14 or 21–23 months with sawdust or dowel inoculations, respectively. None of the co-inoculated species prevented colonization by Heterobasidion annosum; sapwood colonization by Resinicium bicolor may limit growth of H. annosum colonies out of heartwood, reducing the incidence of disease transfer at root contacts. H. annosum colonized stumps despite the presence of competing inoculum. Reduced colonization occurred in paired inoculations with R. bicolor, but not with other fungi. Co-inoculations with Stereum sanguinolentum increased colonization by H. annosum. R. bicolor largely remained in the upper 3–4 cm of stumps and reduced colonization by Melanotus proteus; growth of S. sanguinolentum was completely prevented. The results are discussed in relation to the colonization strategies of the decay fungi, their ability to colonize stumps in the presence of competitors and factors influencing development of communities of decay fungi in stumps.     

Effectiveness of phytoplankton control by large-bodied and small-bodied zooplankton

Employingin situ enclosures containing inocula of the lake zooplankton (mainlyDaphnia galeata, Daphnia cucullata andBosmina spp.) from a moderately eutrophic Lake Ros (Northern Poland) or large-bodiedDaphina magna, the following observations on succession of phytoplankton were made: 1) whereasD. magna could control the density of all the photoplankton size classes, the lake zooplankton could not suppress the large-sized phytoplankters or net phytoplankton; 2) the lake zooplankton was able to control the density of small algae (< 50μm), but its effect on large algae may be opposite: a promotion of net phytoplankton growth by removing small-sized algae which can out-compete net phytoplankton for limited PO₄-P resources (<5μg P l⁻¹). Since efficiency of phytoplankton density control byD. magna decreased with an increase in net phytoplankton abundance, biomanipulation could not be successful without introducing or maintaining a high population of large-bodied cladoceran species before high densities of large algae would make the control of phytoplankton inefficient.     

Cleaner fish become hosts: a novel form of parasite transmission

Adult bucephalid trematodes (Digenea) generally only occur in piscivorous fish. Within labrid fishes they are very rare, however, we have found them in labrid cleaner fish that feed on the ectoparasites of fish. We surveyed 969 labrid fishes from the tropical Pacific and found bucephalids only in cleaners (Labroides dimidiatus, L. bicolor, and Bodianus axillaris) and none in piscivores. The prevalences of bucephalids in L. dimidiatus at Lizard Island, Heron Island, Orpheus Island (all on the Great Barrier Reef), New Caledonia, and Moorea (French Polynesia) were 51, 47, 67, 56, and 67%, respectively. All of the L. bicolor examined from Moorea were infected. Bucephalids were highly prevalent in all size classes of L. dimidiatus from Lizard Island. Bucephalids were found in a 1.6-cm long juvenile L. dimidiatus, in which, piscivory is highly unlikely. We examined the literature on the worldwide bucephalid fauna in labrids and all hosts were found to be cleaners (Symphodus tinca, S. mediterraneus, L. dimidiatus, L. bicolor, and Bodianus axillaris) except Notolabrus parilus, whose ecology is unknown. We suggest that cleaners eat bucephalid metacercariae directly from the exterior surface of client fish during cleaning interactions. This is the first evidence of digeneans in the diet of L. dimidiatus, and the first study to show this novel form of parasite transmission where infective stages are eaten as a result of cleaning behaviour. Cleaning-mediated parasite transmission may result in behavioural modification of second intermediate hosts because clients and parasites both benefit from transmission. If the infection is costly to cleaners and acquired during cheating behaviour, then this parasite might regulate mutualism. Alternatively, if infective stages are targeted, infection by these bucephalids may be a negative consequence of an honest foraging strategy.Communicated by: P. F. Sale     

Toxicity of the new pyrethroid insecticide,deltamethrin, to Daphnia magna

The toxicity of deltamethrin, a synthetic pyrethroid insecticide, was determined under standardized conditions (ISO, 1982) in neonates and juveniles of Daphnia magna. Neonates (6 to 24 h old) were more sensitive than juveniles (48 to 72 h old). The 24- and 48-h EC₅₀s (immobilization) in neonates were 0.113 and 0.031 µg l^–1, respectively. The toxicity of deltamethrin was highly toxic. The 96-h EC₅₀ was in the ppt (µg l^–1) range. Toxicity tests with Daphnia may be used to detect toxic residues in water and sediment in areas treated with deltamethrin and other highly toxic pyrethroid pesticides.     

Mixed Giardia duodenalis assemblage A and E infections in calves

A molecular epidemiological study was conducted on 100 dairy (499 calves) and 50 beef (333 calves) farms in Belgium to estimate the prevalence of different Giardia duodenalis assemblages in calves younger than 10 weeks of age. Positive samples from the epidemiological study and from a previous clinical study were selected and genotyped based on the amplification of the beta-giardin gene. To investigate the occurence of mixed assemblage A and E infections in calves, a novel assemblage-specific PCR was developed based on the triose-phosphate isomerase gene. The prevalence was 22% (95% Probability Interval (PI): 12-34%) in dairy calves and 45% (95% PI: 30-64%) in beef calves. In total, 120 Giardia-positive samples from dairy and beef calves collected in the epidemiological study and from clinically affected calves were identified based on the amplification of the beta-giardin gene. Overall G. duodenalis assemblage E was more prevalent (in 64% of the samples), although the majority (59%) of the dairy calves were infected with G. duodenalis assemblage A. Furthermore, mixed G. duodenalis assemblage A and E infections were identified in 31% of the calf samples (n=101) using the assemblage-specific PCR. We believe this is the first report of mixed infections in calves, and the results of the present study indicate that calves, although mainly infected with the host-specific G. duodenalis assemblage E, are frequently infected with the zoonotic assemblage A, either as a mixed or mono-infection, suggesting that calves might be underestimated as a potential zoonotic reservoir for human infections.