Parasite Infection Dynamics Research Articles

Host lifestyle and parasite interspecific facilitation mediate co‐infection in a species‐poor host–parasite system

Despite their important ecological role, questions remain on mechanisms structuring parasite assemblages. We present an endemic and species‐poor parasite–host system of two species of clupeid fishes Limnothrissa miodon, Stolothrissa tanganicae) and two species of monogenean parasites (Kapentagyrus, Dactylogyridae) from Lake Tanganyika as a model to study parasite distribution patterns and co‐infection dynamics in nature. We modelled spatiotemporal dynamics of parasite–host interaction using infection data along the north–south axis of Lake Tanganyika (660 km) over the course of two seasons and four years (1730 fish, 3710 parasites). We found temporal stability of parasite infection, which contrasts with previously reported seasonally driven fluctuations of fish host abundances. We found a difference in spatial structure between the parasite species which follows the contrasting dispersal pattern of their respective host species. On L. miodon, the host species that is infected by the two parasite species, we discovered a positive correlation with host body size for one parasite species, and a negative correlation for the other species. The apparent host‐size related replacement in the two parasite species infecting L. miodon contrasts with the beneficial influence that each of the parasite species has on the other. Parasites have been reported in previous studies to change habitat depending on host size/age. Differences in abundance and prevalence here reported between parasite species infecting the same host species related to the host body length further illustrate the parasites' dependence on changes in lifestyle of the host during its ontogenetic development. Also, possible mechanisms underlying the reported facilitation of infection are discussed. In conclusion, we show that in this closed, species‐poor system parasite infection dynamics are dependent on a combination of host mobility, host lifestyle changes over ontogenetic development, and interspecific interactions between parasites.

Promise and limitations of 18S genetic screening of extracted fecal DNA from wild capuchins

Genomic screening of fecal DNA provides insight into diet, parasite infection dynamics, and other aspects of the ecology and pathogens of wild populations. Here, we amplify and sequence the V4/V5 regions of the eukaryotic 18S ribosomal RNA gene from fecal DNA of wild capuchin monkeys (Cebus imitator). We collected 94 fecal samples from 26 individuals, each sampled 1-4 times across a 19-month period and examined the eukaryotic diversity in 63 of these samples which had sufficient numbers and quality of reads during downstream analyses. We found a total of 234 distinct amplicon sequence variants (ASVs) classified as Eukaryotes in our samples. Of these, 66 were assigned to the phylum Nematoda. 64 ASVs are from taxa that possibly parasitize monkeys or their food items: 33 were assigned to lungworms (Superfamily Metastrongyloidae; genus Angiostrongylus), two to the genus Strongyloides, and one to the genus Austrostrongylus. The remaining 28 ASVs were assigned to nematodes that likely parasitize plants and/or invertebrates that the monkeys consume. Taken together with past dietary and coprological study of the same primate population, our results suggest that invertebrate consumption and parasitic infection, especially by lungworms, is common and widespread among this population of wild monkeys. We also discuss limitations of our approach, including the amplification of off-target ASVs, and make suggestions for future research. Overall, 18S screening shows promise for identifying various components of the capuchin gastrointestinal eukaryotic ecosystem, including parasitic helminths, and its utility will increase with the improvement of genetic databases.

The impact of innate immunity on malaria parasite infection dynamics in rodent models.

Decades of research have probed the molecular and cellular mechanisms that control the immune response to malaria. Yet many studies offer conflicting results on the functional impact of innate immunity for controlling parasite replication early in infection. We conduct a meta-analysis to seek consensus on the effect of innate immunity on parasite replication, examining three different species of rodent malaria parasite. Screening published studies that span four decades of research we collate, curate, and statistically analyze infection dynamics in immune-deficient or -augmented mice to identify and quantify general trends and reveal sources of disagreement among studies. Additionally, we estimate whether host factors or experimental methodology shape the impact of immune perturbations on parasite burden. First, we detected meta-analytic mean effect sizes (absolute Cohen's h) for the difference in parasite burden between treatment and control groups ranging from 0.1475 to 0.2321 across parasite species. This range is considered a small effect size and translates to a modest change in parasitaemia of roughly 7-12% on average at the peak of infection. Second, we reveal that variation across studies using P. chabaudi or P. yoelii is best explained by stochasticity (due to small sample sizes) rather than by host factors or experimental design. Third, we find that for P. berghei the impact of immune perturbation is increased when young or female mice are used and is greatest when effector molecules (as opposed to upstream signalling molecules) are disrupted (up to an 18% difference in peak parasitaemia). Finally, we find little evidence of publication bias suggesting that our results are robust. The small effect sizes we observe, across three parasite species, following experimental perturbations of the innate immune system may be explained by redundancy in a complex biological system or by incomplete (or inappropriate) data reporting for meta-analysis. Alternatively, our findings might indicate a need to re-evaluate the efficiency with which innate immunity controls parasite replication early in infection. Testing these hypotheses is necessary to translate understanding from model systems to human malaria.

Prevalence and diversity of malaria parasites (genus Plasmodium) in the imperiled Saltmarsh Sparrow are greater at northern sites

Abstract Malaria parasites (genus Plasmodium) are important agents of infectious disease in birds and multiple factors, including warming temperatures and environmental contamination, may act to increase their geographic and host ranges. Here, we examined the role of geographical variation and environmental mercury exposure in malaria parasite infection dynamics in an imperiled songbird species with high mercury exposition, the Saltmarsh Sparrow (Ammospiza caudacutus). Using polymerase chain reaction (PCR) methods, we screened 280 Saltmarsh Sparrows from across their breeding range for malaria parasite infection. We detected malaria parasites in 17% of sampled birds and a total of 6 Plasmodium lineages. Prevalence of infection and diversity of parasite lineages varied across the breeding range of the Saltmarsh Sparrow and increased at more northern latitudes. Although mercury is a known immunosuppressant and has been documented to alter an individual’s susceptibility to pathogens, we did not find a significant difference in blood mercury levels between infected and not infected birds, perhaps due to sampling methods and/or small sample sizes. As a specialist of coastal wetlands, the Saltmarsh Sparrow is an excellent indicator species for ecological health, and the patterns of malaria parasite infection with host distribution and mercury suggest that birds at northern latitudes are at greater risk of disease and should be priorities for conservation, habitat, and pathogen monitoring.

Linked foraging and bioenergetics modeling may inform fish parasite infection dynamics

Linked foraging and bioenergetics modeling may inform fish parasite infection dynamics

Extrinsic and intrinsic drivers of parasite prevalence and parasite species richness in a marine bivalve.

Parasite species richness is influenced by a range of drivers including host related factors (e.g. host size) and environmental factors (e.g. seawater temperature). However, identification of modulators of parasite species richness remains one of the great unanswered questions in ecology. The common cockle Cerastoderma edule is renowned for its diversity and abundance of parasites, yet drivers of parasite species richness in cockles have not been examined to investigate the association of both macro and microparasite communities. Using cockles as a model species, some of the key drivers of parasite prevalence and parasite species richness were investigated. Objectives of this 19-month survey were to determine the influence of the environment, host-parasite dynamics and parasite associations on parasite species richness and prevalence at two different geographic latitudes, chosen based on environmental differences. The highest parasite species richness was recorded in the northern sites, and this was potentially influenced by a range of interactions between the host, the pathogens and the environment. Parasite prevalence increased with host size and age, and parasite species richness increased with reduced salinity. A number of interactions between parasites, and between parasites and pathologies may be influencing parasite infection dynamics. New and concerning information is also presented regarding interactions between parasites and their environment. A number of parasites and potential pathogens (bacteria, Trichodina ciliates, metacercariae, trematode sporocysts) may be advantaged under climate change conditions (warming seas, increased precipitation), increasing disease incidence, which may prove detrimental not just for cockles, but for other bivalve species in the future.

Comparative assessment of metazoans infestation of Nile tilapia (Oreochromis niloticus) (L.) (Perciformes: Cichlidae) in floating cages and ponds from Chiapas, Mexico.

Nile tilapia is the most commercially important fish in Chiapas as well as in other parts of the world. An understanding of parasite infection dynamics in tilapia may assist in applying proper prophylactic measures for reducing the loss of fish caused by parasitic diseases. Different environments and culture systems may imply different infection dynamics; therefore, the present study identified and compared the infection parameters (prevalence, mean abundance, and intensity) of parasites of Oreochromis niloticus cultured in floating cages and ponds. A total of 18 metazoan parasite taxa were recovered from gills, skin, fins and intestines of 310 specimens from floating cages and ponds. Fourteen species of parasites were found in floating cages: 8 monogenean species, 1 nematode, 1 digenea, 1 crustacea, 3 protozoans. In ponds, 16 parasite taxa were reported: 11 were monogeneans species, 4 protozoans and 1 crustacean. In both systems, monogeneans (Cichlidogyrus sclerosus, C. tilapiae, Gyrodactylus cichlidarum) and protozoans (Trichodina compacta) were most prevalent. Tilapia in ponds sustained higher parasitic infections than those in floating cages (p<0.05). The Canonical Correspondence Analysis showed two groups: the first grouped the ponds, associated with high values of nitrite, nitrate, ammonia, conductivity, temperature, and the abundance of the ectoparasites C. halli, C. dossoui, Scutogyrus longicornis, C. sclerosus and T. compacta. The second group grouped the cages, associated with Clinostomum marginatum, Apiosoma piscicola, Lernea sp., and Contracaecum sp. and a high dissolved oxygen concentration. Our findings suggest that monitoring programs are required to improve the sanitary conditions of tilapia cultures in Chiapas.

Demographic history and population genetic structure of Anisakis pegreffii in the cutlassfish Trichiurus japonicus along the coast of mainland China and Taiwan.

Studying the genetic diversity of nematode parasite populations is crucial to gaining insight into parasite infection dynamics and informing parasite phylogeography. Anisakiasis is a zoonotic disease caused by the consumption of infectious third-stage larvae (L3) of Anisakis spp. carried by marine fish. In the present study, a total of 206 mitochondrial DNA sequences (cytochrome c oxidase 2, cox2) were used to study the genetic diversity, genetic structure, and historical demography of twelve A. pegreffii populations from Trichiurus japonicas along the coast of mainland China and Taiwan. Two distinct evolutionary lineages of A. pegreffii and no significant genealogical structures corresponding to sampling localities suggested that isolation in the marginal seas shaped their patterns of phylogeographic distribution along the coast of mainland China and Taiwan during glaciation with lower sea levels. Furthermore, pairwise FST values and AMOVA did not indicate any significant genetic differentiation among groups with no relation to the geographic area, which might be attributed to fewer barriers to gene flow as well as large population sizes. The results of the neutrality test, mismatch distribution, and Bayesian skyline plot analyses showed that entire population underwent population expansion during the late Pleistocene. Analysis of the demographic history revealed that A. pegreffii underwent historical lineage diversification and admixture due to secondary contact based on ABC analysis. The present research represents the first definitive population structure and demographic history across sampling locations of A. pegreffii along the coast of mainland China and Taiwan.

Trichomonas vaginalis follow-up and persistence in Colombian women

Trichomonas vaginalis (TV), the most common non-viral sexually-transmitted infection is considered a neglected infection and its epidemiology is not well known. This study determined TV-infection dynamics in a retrospective cohort of Colombian women and evaluated associations between risk factors and TV-outcome. TV was identified by PCR. Cox proportional risk models were used for evaluating the relationship between TV-outcome (infection, clearance and persistence) and risk factors (sexually-transmitted infections and sociodemographic characteristics). Two hundred and sixty-four women were included in the study; 26.1% had TV at the start of the study, 40.9% suffered at least one episode of infection and 13.0% suffered more than one episode of TV during the study. Women suffering HPV had a greater risk of TV-infection (aHR 1.59), high viral-load (> 102) for HPV-16 being related to a greater risk of persistent parasite infection; a high viral load (> 102) for HPV-18 and -33 was related to a lower probability of TV-clearance. Ethnicity (afrodescendent/indigenous people: aHR 5.11) and having had more than two sexual partners (aHR 1.94) were related to greater risk of infection, contrasting with women having a background of abortions and lower probability of having TV (aHR 0.50). Women aged 35- to 49-years-old (aHR 2.08), increased years of sexual activity (aHR 1.10), multiple sexual partners (aHR 8.86) and multiparous women (aHR 3.85) led to a greater probability of persistence. Women whose cervical findings worsened had a 9.99 greater probability of TV-persistence. TV distribution was high in the study population; its coexistence with HPV and other risk factors influenced parasite infection dynamics. The results suggested that routine TV detection should be considered regarding populations at risk of infection.

Trypanosome Signaling-Quorum Sensing.

African trypanosomes are responsible for important diseases of humans and animals in sub-Saharan Africa. The best-studied species is Trypanosoma brucei, which is characterized by development in the mammalian host between morphologically slender and stumpy forms. The latter are adapted for transmission by the parasite's vector, the tsetse fly. The development of stumpy forms is driven by density-dependent quorum sensing (QS), the molecular basis for which is now coming to light. In this review, I discuss the historical context and biological features of trypanosome QS and how it contributes to the parasite's infection dynamics within its mammalian host. Also, I discuss how QS can be lost in different trypanosome species, such as T. brucei evansi and T. brucei equiperdum, or modulated when parasites find themselves competing with others of different genotypes or of different trypanosome species in the same host. Finally, I consider the potential to exploit trypanosome QS therapeutically.

Gastrointestinal nematode and Eimeria spp. infections in dairy cattle along a rural-urban gradient.

Endoparasite infections can lead to considerable economic losses in dairy cattle due to decreases in milk yield and quality. Environmental and host-related factors contribute to endoparasite infection intensity and probability. Moreover, advancing urbanization influences parasite infection dynamics in livestock due to close human-animal cohabitation and changes in animal housing conditions. The aim of the present study was to investigate social-ecological effects on gastrointestinal nematode (GIN) and Eimeria spp. infections in dairy cattle along a rural-urban gradient in the emerging Indian megacity Bangalore. In this regard, 726 faecal samples from 441 dairy cattle of different ages and physiological stages were collected from 101 farms and examined at three visits between June 2017 and April 2018. Based on a survey stratification index (SSI) comprising built-up density and distance to the city center, we assigned the farms to urban, mixed and rural areas. GIN eggs were identified in the faeces of 243 cattle (33.5%; 95% confidence interval [CI]: 30.1-36.9%), and Eimeria spp. oocysts in the faeces of 151 cattle (20.8%; 95% CI: 17.9-23.7%). Co-infection rates of GIN and Eimeria spp. were 8.5 to 12.2% higher in rural compared to urban and mixed areas. The SSI effect significantly influenced Eimeria spp. infection probability and oocyst per gram of faeces (OpG; P<0.001) with an infection probability and OpG higher than 26% and 40% for cattle kept in rural areas compared to cattle from urban areas. However, the SSI effect was not significant for the infection probability of GIN and for GIN eggs per gram of faeces (EpG). Infection probabilities and EpG/OpG were significantly higher in calves and heifers compared to lactating and dry cows. Moreover, we estimated significantly lower OpG values in summer compared to the other seasons. No differences were estimated for GIN and Eimeria spp. infection probabilities and EpG/OpG with regard to pasture access and breed. The variations in endoparasite infection intensity and probability observed along the rural-urban gradient of Bangalore reflect the variability in dairy husbandry systems governed by the social-ecological context.

Determinants of Eimeria and Campylobacter infection dynamics in UK domestic sheep: the role of co-infection.

Coccidiosis caused by Eimeria species is a well-recognized disease of livestock. Enteric Eimeria infections are common, but disease usually only manifests when infection intensity is abnormally high. Campylobacter species are important zoonotic enteric bacterial pathogens for which livestock are important reservoir hosts. The diversity and epidemiology of ovine Eimeria and Campylobacter infections on two farms in north-western England were explored through a 24-month survey of shedding in sheep feces. Most animals were infected with at least one of 10 different Eimeria species, among which E. bakuensis and E. ovinoidalis were most common. An animal's age and the season of sampling were associated with the probability and intensity of Eimeria infection. Season of sampling was also associated with the probability of Campylobacter infection. Interestingly, higher intensities of Eimeria infections were significantly more common in animals not co-infected with Campylobacter. We explored the determinants of E. bakuensis and E. ovinoidalis infections, observing that being infected with either significantly increased the likelihood of infection with the other. The prevalence of E. ovinoidalis infections was significantly lower in sheep infected with Campylobacter. Recognition that co-infectors shape the dynamics of parasite infection is relevant to the design of effective infection control programmes.

Some like it hotter: trematode transmission under changing temperature conditions.

Climate change-related increases in temperature will influence the interactions between organisms, including the infection dynamics of parasites in ecosystems. The distribution and transmission of parasites are expected to increase with warmer temperature, but to what extent this will affect closely related parasite taxa living in sympatry is currently impossible to predict, due to our extremely limited understanding of the interspecific variation in transmission potential among parasite species in changing ecosystems. Here, we analyse the transmission patterns of four trematode species from the New Zealand mudsnail Potamopyrgus antipodarum with different life cycles and transmission strategies under two temperature scenarios, simulating current and future warmer temperatures. In a comparative experimental study, we investigated the effects of temperature on the productivity, movement and survival of the parasites' transmission stages (cercariae) to quantify the net effect of temperature on their overall transmission potential. Our results show that increases in temperature positively affect cercarial transmission dynamics, yet these impacts varied considerably between the cercariae of different trematode species, depending on their host-searching behaviour. These different species-specific transmission abilities as well as the varying individual patterns of productivity, activity and longevity are likely to have far-reaching implications for disease dynamics in changing ecosystems, since increases in temperature can shift parasite community structure. Due to the parasites' capacity to regulate the functioning of whole ecological communities and their potential impact as disease agents, understanding these species-specific parasite transmission traits remains a fundamental requirement to predict parasite dynamics under changing environmental conditions.

Effect of environmental factors on survival and population growth of ciliated parasite, Mesanophrys sp. (Ciliophora: Scuticociliatia) infecting Portunus trituberculatus.

Mesanophrys sp. is a newly identified parasitic ciliate infecting farmed swimming crab. To demonstrate the correlation between parasite development and environmental conditions, this study aimed to investigate the effect of temperature, salinity, pH and frequency of passage of parasite on survival, growth and body size of Mesanophrys sp. in vitro. The results revealed that survival, population density and growth rate of the parasite were highest at 12°C and decreased with increasing temperature from 16 to 26°C. In addition, the survival, population density and growth rate of Mesanophrys sp. were high at 20‰. When salinity was adjusted to levels lower (0-10‰) and higher (40-60‰) than 20‰, the parasite's survival and growth rate gradually declined. The optimal pH for parasite survival was 8.0, whereas its survival was inhibited at <4.5 or >9.5. Our result also showed that parasite body proportions (length:width) were significantly smaller at the highest temperature compared to the lower temperature, whereas different salinities had no significant effect. Furthermore, we introduced dynamic parasite culture systems in vitro where Mesanophrys sp. was cultured in medium-containing culture plates through continually reducing and halving the old medium into fresh. Application of this optimized dilution timing technique with fresh medium and sub-cultured enabled a continuous culture of parasites. Under this optimized condition, the highest population density and exponential growth rate of the parasite were achieved than that of a control group. This study will help to understand the ciliated parasite infection dynamics and provides new possibilities for in vitro parasite-associated studies.

Characterization of viruses in a tapeworm: phylogenetic position, vertical transmission, and transmission to the parasitized host

Parasitic flatworms (Neodermata) infect all vertebrates and represent a significant health and economic burden worldwide due to the debilitating diseases they cause. This study sheds light for the first time into the virome of a tapeworm by describing six novel RNA virus candidate species associated with Schistocephalus solidus, including three negative-strand RNA viruses (order Jingchuvirales, Mononegavirales, and Bunyavirales) and three double-stranded RNA viruses. Using in vitro culture of S. solidus, controlled experimental infections and field sampling, we demonstrate that five of these viruses are vertically transmitted, and persist throughout the S. solidus complex life cycle. Moreover, we show that one of the viruses, named Schistocephalus solidus rhabdovirus (SsRV1), is excreted by the parasite and transmitted to parasitized hosts indicating that it may impact S. solidus–host interactions. In addition, SsRV1 has a basal phylogenetic position relative to vertebrate rhabdoviruses suggesting that parasitic flatworms could have contributed to virus emergence. Viruses similar to four of the S. solidus viruses identified here were found in geographically distant S. solidus populations through data mining. Further studies are necessary to determine if flatworm viruses can replicate in parasitized hosts, how they contribute to parasite infection dynamics and if these viruses could be targeted for treatment of parasitic disease.

The effects of environmental and nutritional conditions on the development of Perkinsus olseni prezoosporangia

Perkinsus olseni is a widely distributed protozoan pathogen that infects a wide range of marine mollusks. Prezoosporulation of P. olseni trophozoites is easily observed in Ray's fluid thioglycollate medium, but in nature, trophozoites within host tissue should be able to develop into prezoosporangia without any additional artificial medium after the host dies. How this process might work in field conditions remains poorly understood, however, partly because of the lack of appropriate in vitro assays. In this study, we observed that trophozoites of P. olseni successfully developed into prezoosporangia when mixed with minced tissue of the Manila clam Ruditapes philippinarum and placed in seawater. We were thus able to establish a new method to examine the development of P. olseni to prezoosporangia under artificially simulated natural environmental conditions. Using this method, we found that low temperatures (5 °C, 15 °C) significantly suppressed prezoosporangia development. In addition, we found that prezoosporangia were developed in a wide range of salinities (10–50 practical salinity unit) and that P. olseni requires some nutrition factors from host tissue for prezoosporulation to occur. Because the transmission of P. olseni among a host population highly depends on the developmental process of prezoosporangia, which leads to production of the infective zoospore stage, these results will help further our understanding of the parasite's infection dynamics in nature.

Variation in Local and Systemic Pro-Inflammatory Immune Markers of Wild Wood Mice after Anthelmintic Treatment.

The immune system represents a host’s main defense against infection to parasites and pathogens. In the wild, a host’s response to immune challenges can vary due to physiological condition, demography (age, sex), and coinfection by other parasites or pathogens. These sources of variation, which are intrinsic to natural populations, can significantly impact the strength and type of immune responses elicited after parasite exposure and infection. Importantly, but often neglected, a host’s immune response can also vary within the individual, across tissues and between local and systemic scales. Consequently, how a host responds at each scale may impact its susceptibility to concurrent and subsequent infections. Here we analyzed how characteristics of hosts and their parasite infections drive variation in the pro-inflammatory immune response in wild wood mice (Apodemus sylvaticus) at both the local and systemic scale by experimentally manipulating within-host parasite communities through anthelmintic drug treatment. We measured concentrations of the pro-inflammatory cytokine tumor necrosis factor alpha (TNF-α) produced in vitro in response to a panel of toll-like receptor agonists at the local (mesenteric lymph nodes [MLNs]) and systemic (spleen) scales of individuals naturally infected with two gastrointestinal parasites, the nematode Heligmosomoides polygyrus and the protozoan Eimeria hungaryensis. Anthelmintic-treated mice had a 20-fold lower worm burden compared to control mice, as well as a four-fold higher intensity of the non-drug targeted parasite E. hungaryensis. Anthelmintic treatment differentially impacted levels of TNF-α expression in males and females at the systemic and local scales, with treated males producing higher, and treated females lower, levels of TNF-α, compared to control mice. Also, TNF-α was affected by host age, at the local scale, with MLN cells of young, treated mice producing higher levels of TNF-α than those of old, treated mice. Using complementary, but distinct, measures of inflammation measured across within-host scales allowed us to better assess the wood mouse immune response to changes in parasite infection dynamics after anthelmintic treatment. This same approach could be used to understand helminth infections and responses to parasite control measures in other systems in order to gain a broader view of how variation impacts the immune response.

Parasitic nematodes simultaneously suppress and benefit from coccidian coinfection in their natural mouse host.

Within-host interactions among coinfecting parasites are common and have important consequences for host health and disease dynamics. However, these within-host interactions have traditionally been studied in laboratory mouse models, which often exclude important variation and use unnatural host-parasite combinations. Conversely, the few wild studies of within-host interactions often lack knowledge of parasite exposure and infection history. Here we exposed laboratory-reared wood mice (Apodemus sylvaticus) that were derived from wild-caught animals to two naturally-occurring parasites (nematode: Heligmosomoides polygyrus, coccidia: Eimeria hungaryensis) to investigate the impact of coinfection on parasite infection dynamics, and to determine if the host immune response mediates this interaction. Coinfection led to delayed worm expulsion and prolonged egg shedding in H. polygyrus infections and lower peak E. hungaryensis oocyst burdens. By comparing antibody levels between wild and colony-housed mice, we also found that wild mice had elevated H. polygyrus-IgG1 titres even if currently uninfected with H. polygyrus. Using this unique wild-laboratory system, we demonstrate, for the first time, clear evidence for a reciprocal interaction between these intestinal parasites, and that there is a great discrepancy between antibody levels measured in the wild vs those measured under controlled laboratory conditions in relation to parasite infection and coinfection.

The Long-Term Dynamics of Parasite Infection in Coregonids with Different Food Specializations

The long-term dynamics of the parasitic infection of two coregonid species with different food specializations, peled Coregonus peled (Gmelin, 1789) and Siberian whitefish Coregonus lavaretus pidschian (Gmelin, 1788), during spawning migration in the Synya River (a Polar Urals tributary of the Lower Ob) has been studied. The differences in the parasite species composition and infection of the two fish species are determined their food spectra features, as well as by their use of different biotopes in feeding water bodies and the interannual dynamics of the fish age composition. A trend towards a decrease in the rate of peled infection by myxosporidium and cestode with a simultaneous decrease in its abundance due to intensive catches has been revealed. The stability of the composition of the coregonid parasite fauna in the Ob lower reaches indicates stable relationships between parasites and hosts and a relatively stable state of the ecosystem of the Lower Ob.

A Long Temporal Study of Parasitism in Asexual-Sexual Populations of Carassius gibelio: Does the Parasite Infection Support Coevolutionary Red Queen Dynamics?

Carassius gibelio is an extraordinary cyprinid species exhibiting both sexual and asexual reproduction. We hypothesized that parasitism selection is one of the potential mechanisms contributing to the coexistence of the two reproductive forms of C. gibelio living in the same habitat. We performed a four-year study to investigate the dynamics of parasite infection in C. gibelio. According to the Red Queen prediction, the asexual form is a target of parasite adaptation due to its low genetic variability. Both sexual and gynogenetic forms of C. gibelio exhibited similar levels of prevalence, with monogeneans being the most frequently observed parasite group. We observed the temporal dynamics of parasite infection in the last year of investigation, when both forms were more strongly parasitized. The sexual form was more parasitized by ectoparasites in the first and last years and less parasitized by nematodes in the last year when compared to the gynogenetic form. We found no trend of high parasite infection in gynogenetic mtDNA haplotypes. We conclude that Red Queen dynamics is not the mechanism driving parasite infection in sexual-gynogenetic C. gibelio over a long time scale. Alternatively, we suggest that the dynamics of parasite infection in this complex may be generated by multiple mechanisms.