Combined Effects Of Parasites Research Articles

Potential Benefits of Acanthocephalan Parasites for Chub Hosts in Polluted Environments.

Some parasites are expected to have beneficial impacts on wild populations in polluted environments because of their bioaccumulation potential of pollutants from their hosts. The fate of organic micropollutants in host-parasite systems and the combined effect of parasitism and pollution were investigated in chub Squalius cephalus, a freshwater fish, infected (n = 73) or uninfected (n = 45) by acanthocephalan parasites Pomphorhynchus sp. from differently contaminated riverine sites. Several ubiquitous pollutants (polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), polybrominated diphenyl-ethers (PBDEs), polycyclic aromatic hydrocarbons (PAHs), phthalates, insecticides, pyrethroids, and N,N-diethyl-meta-toluamide (DEET)) and some of their metabolites were characterized for the first time in parasites and various fish matrices (muscle, liver, and stomach content). Most organic pollutants reached higher levels in parasites than in chub matrices. In contrast, metabolite levels were lower in parasite tissues compared to fish matrices. Infected and uninfected chub exhibited no significant differences in their pollutant load. Body condition, organo-somatic indices, and immunity were not affected by parasitism, and few correlations were found with chemical pollution. Interestingly, infected chub exhibited lower oxidative damage compared to uninfected fish, irrespective of their pollutant load. In light of these results, this correlative study supports the hypothesis that acanthocephalan parasites could bring benefits to their hosts to cope with organic pollution.

Anti-parasite treatment results in decreased estimated survival with increasing lead (Pb) levels in the common eider Somateria mollissima.

Field experiments where parasites are removed through treatment and contaminant levels in host tissues are recorded can provide insight into the combined effects of parasitism and contaminants in wild populations. In 2013 and 2014, we treated northern common eider ducks (Somateria mollissima) arriving at a breeding colony with either a broad-spectrum antihelminthic (PANACUR®) or distilled water, and measured their blood lead (Pb) levels. Breeding propensity and clutch sizes were inversely related to Pb in both treatment groups. In comparison, a negative effect of Pb on resight probability the following year was observed only in the anti-parasitic treatment (APT) group. These contrasting patterns suggest a long-term benefit to survival of intestinal parasitism in eiders experiencing Pb exposure. The arrival date of hens explained some, but not all, of the effects of Pb. We weigh the merits of different hypotheses in explaining our results, including protective bioaccumulation of Pb by parasites, condition-linked thresholds to costly reproduction and the direct effects of APT on eider health. We conclude that variation in helminth parasitism influences survival in this migratory bird in counterintuitive ways.

Additive effects of temperature and infection with an acanthocephalan parasite on the shredding activity of Gammarus fossarum (Crustacea: Amphipoda): the importance of aggregative behavior.

Climate change can have critical impacts on the ecological role of keystone species, leading to subsequent alterations within ecosystems. The consequences of climate change may be best predicted by understanding its interaction with the cumulative effects of other stressors, although this approach is rarely adopted. However, whether this interaction is additive or interactive can hardly be predicted from studies examining a single factor at a time. In particular, biotic interactions are known to induce modifications in the functional role of many species. Here, we explored the effect of temperature on leaf consumption by a keystone freshwater shredder, the amphipod Gammarus fossarum. This species is found at high densities in the wild and relies on aggregation as an antipredator behavior. In addition, gammarids regularly harbor acanthocephalan parasites that are known to induce multiple effects on their hosts, including modifications on their functional role. We thus assessed the cumulative effect of both intraspecific interactions and parasitism. Consumption tests were conducted on gammarids, either naturally infected with Pomphorhynchus tereticollis or uninfected, feeding alone or in groups. Our results show that increased temperatures induced a significant increase in consumption, but only to a certain extent. Interestingly, consumption at the highest temperature depended on amphipod density: Whereas a decrease was observed for single individuals, no such effect on feeding was observed for individuals in groups. In addition, infection by acanthocephalan parasites per se significantly negatively impacted the shredding role of gammarids. Overall, the combined effects of parasitism and temperature appeared to be additive. Thus, future studies focusing on the impact of climate change on the functional role of keystone species may benefit from a multimodal approach under realistic conditions to derive accurate predictions.

Complex dynamics of a predator–prey–parasite system: An interplay among infection rate, predator's reproductive gain and preference

Parasites are considered as an important factor in regulating their host populations through trait-mediated effects. On the other hand, predation becomes particularly interesting in host–parasite systems because predation can significantly alter the abundance of parasites and their host population. The combined effects of parasites and predator on host population and community structure therefore may have larger effect. Different field experiments confirm that predators consume disproportionately large number of infected prey in comparison to their susceptible counterpart. There are also substantial evidences that predator has the ability to distinguish prey that have been infected by a parasite and avoid such prey to reduce fitness cost. In this paper we study the predator–prey dynamics, where the prey species is infected by some parasites and predators consume both the susceptible and infected prey with some preference. We demonstrate that complexity in such systems largely depends on the predator's selectivity, force of infection and predator's reproductive gain. If the force of infection and predator's reproductive gain are low, parasites and predators both go to extinction whatever be the predator's preference. The story may be totally different in the opposite case. Survival of species in stable, oscillatory or chaotic states, and their extinction largely depend on the predator's preference. The system may also show two coexistence equilibrium points for some parameter values. The equilibrium with lower susceptible prey density is always stable and the equilibrium with higher susceptible prey density is always unstable. These results suggest that understanding the consequences of predator's selectivity or preference may be crucial for community structure involving parasites.

Combined effects of parasites, climate and pollution on brown trout, Salmo trutta, in Swiss rivers

Combined effects of parasites, climate and pollution on brown trout, Salmo trutta, in Swiss Rivers

Parasitism interacts with mutual interference to limit foraging efficiency in larvae of Nephus includens (Coleoptera: Coccinellidae)

Predator parasitism can modify predator–prey interactions through long-term (numerical) and short-term (functional response) impacts. However, mutual interference is another density-dependent factor that may affect predator foraging efficiency in the presence or absence of parasitism. This study examined the effects of parasitism of the invader Nephus includens (Kirsch) (Coleoptera: Coccinellidae) by Homalotylus flaminius Dalman (Hymenoptera: Encyrtidae), predator density, and prey density on the searching efficiency (a measure of area of discovery) using the cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae) as alternate prey. Mutual interference reduced foraging efficiency by 47% in parasitized fourth-instar larvae compared to 44% in those unparasitized. Increasing predator density decreased searching efficiency more markedly in parasitized than in unparasitized larvae. The combined effects of parasitism and mutual interference reduced searching efficiency by 91%. Conversely, prey consumption by parasitized fourth-instar increased with increasing prey density, thus interference values declined from 0.98 to 0.82, indicating that the negative effect of parasitism on predator foraging diminished with increasing prey availability. Thus, these results support the inference of the ‘enemy release’ hypothesis, that invading predators may be more successful and have higher impacts on prey when they escape from parasitism. In the context of augmentation of N. includens in Egypt, releases of predator life stages immune to parasitism, by H. flaminius, (e.g., pupae or adults) in a suitable predator–prey ratio, especially early season, should minimize the detrimental effects of parasitism and intraspecific interference on foraging behavior, thus increasing predator ability to build up its population on alternative prey (aphid) and to attack later occurring target prey (mealybugs).

Combined effects of parasites and contaminants on animal health: parasites do matter

The cumulative effects of multiple stressors are becoming a priority concern for ecotoxicologists, ecologists and conservation biologists working to understand threats to ecosystems and species. In that context, parasites and pathogens are increasingly a focus of attention. Parasites interact with natural and anthropogenic stressors to increase mortality and reduce animal health in myriad ways in a wide spectrum of host and parasite taxa. The combined effects of parasites and other stressors can reduce either resistance or tolerance to infection. Recommendations are provided to guide further research.

The role of the invasive snail Potamopyrgus antipodarum in the transmission of trematode parasites in Europe and its implications for ecotoxicological studies

Potamopyrgus antipodarum is an invasive freshwater mollusc in Europe introduced from Australasia in the late 19th century and now commonly distributed throughout the continent. It has frequently been used as a model species for a range of ecological disciplines, and recently has been increasingly utilised for ecotoxicological work, particularly the impact of endocrine disrupting chemicals. However, molluscs are commonly infected with trematode parasites, which can disrupt a range of ecological and physiological host functions including the endocrine system, and may be an undetected source of distortion for pollution studies. It is therefore important to know what role P. antipodarum may play in the transmission of trematodes in Europe. This study assessed the extent of trematode parasitism in P. antipodarum European populations, from both indigenous parasite species and those introduced accidentally through the international trade in fish and birds. In addition, the combined effects of parasitism and pollution on molluscan physiology and ecology is summarized and the implications for ecotoxicological studies using P. antipodarum evaluated.

Reduced survivorship of Himasthla (Trematoda, Digenea)-infected cockles ( Cerastoderma edule) exposed to oxygen depletion

Bivalve populations from inshore waters often accommodate a diverse trematode fauna that may have a variety of effects on host specimens. In particular, larval trematodes that grow or reproduce within their host are known to be severe pathogens, whereas trematodes utilising bivalves only for encystment are thought to be relatively benign. Yet this may depend on the environmental conditions, and it can be expected that such trematodes in concert with other stress agents can be detrimental to host organisms. To examine the impact of such larval trematodes on hosts subjected to stress, we studied the digenetic trematode Himasthla elongata and one of its second intermediate hosts, the bivalve Cerastoderma edule. Experimentally infected cockles and non-infected cockles were exposed to oxygen depletion, whereupon we measured their burrowing ability and survivorship. After 30 h of hypoxia, the survival of infected cockles was significantly reduced compared to non-infected cockles, whereas no effect of parasites on cockles under normoxic conditions was found. In addition, parasites tended to reduce the burrowing ability of cockles exposed to hypoxia but the effect was not clear. The effect of parasites and possible ecological consequences are discussed and it is suggested that the combined effects of parasites and oxygen deficiency may explain some hitherto unexplained cases of mass mortalities in bivalve populations.

Combined effects of parasitism and desiccation on mortality of the soil-dwelling mites, Scheloribates laevigatus and Galumna flabellifera

Combined effects of parasitism and desiccation on mortality of the soil-dwelling mites, Scheloribates laevigatus and Galumna flabellifera

Effects of chronic exposure to petroleum hydrocarbons on two species of marine fish infected with a hemoprotozoan, Trypanosoma murmanensis

The present study was undertaken to ascertain the effects of a blood protozoan, Trypanosoma murmanensis, on two species of marine fish exposed to petroleum hydrocarbons. Infected juvenile and adult winter flounder were exposed for 6 weeks to sediment contaminated with a Venezuelan crude (total hydrocarbon concentration, 2600–3200 μg/g) whereas Atlantic cod were exposed to water-accommodated fractions (50–100 μg/L) for 12 weeks. Three other groups, uninfected controls, fish infected with trypanosomes only, and oil-treated, uninfected fish, were held in aquaria in a continuously flowing seawater system. Mortality was higher in the infected, oil-treated flounder and subadult cod than in the trypanosome-infected only, oil-treated, and control groups. Death in oil-treated flounder was associated with severe tail rot and hypersecretion of mucus from the gills, whereas blood values (hematocrit, hemoglobin, total plasma protein) were significantly depressed in both infected groups. Low body condition, excessive mucus secretion by the gills, and retarded gonadal development were observed in adult, oil-treated cod but these were more pronounced in the infected, oil-treated groups. Prevalence of the infection and parasitemias were higher in the oil-treated groups than in untreated fish. These results provide evidence that the combined effects of parasites and chronic oil pollution can not only cause mortality but can also jeopardize health and reproduction in surviving fish.

Origin and Decline of the 1973 Plague Locust Outbreak in Central Western New South Wales.

An important outbreak of the Australian plague locust, Chortoicetes terminifera (Wlk.), occurred in 1973 in central western New South Wales. The dynamics of the outbreak could be resolved into a sequence of five principal interacting events: (1) Sustained population increases in low-density populations in northern central western New South Wales during three successive breeding periods in 1972. The increases were a result of successful, local multiplication, immigration from more northerly breeding areas and restricted opportunities for dispersal. The continuing concentration of locusts in the northern central west led to local gregarisation and swarm formation in autumn and spring 1972. (2) Massive southward displacements at night during an intense tropical disturbance between 29 January and 4 February 1973, which resulted in an invasion and concentration of infestations in southern central western New South Wales. (3) Substantial multiplication increases (10- to 30-fold), as a result of the drought-breaking rainfall in the autumn and spring of 1973 in the central-west. This resulted in an intensification of the plague with the production of numerous, slow-moving swarms. (4) Massive southward displacements during several periods of disturbed weather in spring 1973, which led to the disappearance of adult infestations from the central west and a dispersal of infestations in areas invaded further south. (5) Heavy mortality in residual populations of hoppers and eggs. The combined effects of parasites, predators and a reduced viability of eggs and hoppers resulted in a complete collapse of the plague in the central west by December 1973.Although displacement by adults at night is shown to be the principal factor regulating both population fluctuations in specific localities and the spread of plagues through southward invasions, outbreaks are ultimately determined by initial multiplication increases in relatively sedentary recession populations. Both multiplication and migration were influenced more by variations in synoptic weather than by any other factor. Diurnal swarm movements, although conspicuous, did not significantly influence the overall spread of the outbreak studied.The quality and quantity of available fresh green food did not appear to limit further successful breeding during the decline of the plague. Although influxes of locusts into the central-west continued during disturbed weather in 1974, none remained to breed and densities fell to levels (<1/ha) lower than those of drought seasons. It appears unlikely, therefore, that plagues can be sustained in any one area, even when environmental conditions remain favourable for breeding, because of: (1) mass emigration during disturbed weather; (2) increased effectiveness of natural enemies; and (3) declines in viability and fecundity in moist conditons.

The Bionomics of Glossina morsitans in the Umniati Fly Belt, Southern Rhodesia, 1922–23

The pupal period has been shown to be between three and four times as long during the winter months as it is in the summer months.Breeding continues the whole year round, but the period of greatest density and activity is in September, i.e., towards the end of the dry season. During a period of heavy rains, long grass and full forest foliage, puparia were fairly abundant, while density counts did not indicate any lack of nourishment. The grass in these mopane belts, however, never grows very long.All types of forest were used for breeding except the heavy river forest. In the mopane a heavy reduction in density occurred after leaf-fall. At the end of the dry season the dry bed of a small well-shaded stream was used extensively as a breeding place. Heavy thorn thickets (Isinanga) and overgrown dongas were only used as breeding places after most of the leaves had fallen.The puparia are attacked by at least seven species of insect parasites. Of these Mutilla glossinae and possibly two species of Bombyliids are the most important. These parasites show definite seasonal activity. At the end of the dry season, 84 per cent. of all emergences were parasites.The percentage of collected puparia which failed to yield either flies or parasites increased from 23 per cent. in March to 60 per cent. in November. Experiments showed that half an hour's exposure to the sun (118° F.), even when covered with about one inch of sand, was sufficient to kill the puparia.The combined effect of parasitism and the hot summer sun on deposited puparia is no doubt a contributary cause of the great fall in density that occurs throughout mopane forest at the end of the late dry season after leaf-fall is complete. This statement does not necessarily apply to other areas not examined.This fly belt has continued to spread and game has increased, although the area has been thrown open to free shooting since 1905. Between 1924 and 1925 the spread eastward has been rapid, and new settlement areas have been endangered.