Seasonal dynamics of the component community structure of parasites of the minnow Phoxinus phoxinus (L.)

The material represented by 75 specimens of minnow of the age 2-2(+) was collected according to the standard technique in the Chovju River (tributary of the Vychegda River, a region of the settlement Nizniy Chov, district of Syktyvkar town) during the period June-September 2000. The quantitative estimation of the structure of the component parasite communities was performed by calculating errors of the equation of regression for each species group separately, with subsequent summarizing of means of errors by all parasite groups comprising the community (Dorovskikh, 2001 6; 2002 B). In order to have a possibility to get data complementing each other, the calculation of variety indexes and other indexes have been made for metazoan parasites only and for the whole community, including the protozoan parasites. In both cases, i.e. considering only metazoan parasites and the whole composition of parasite species, three states of the component parasite community have been recognised: the formed community (June), the community in destroying (July and August), the community in the process of formation (September). In the course of working on the total species composition we recorded the beginning of community destroying on 30th of June, and the beginning of community formation in August. Considering only the metazoan parasites, the community is defined (after: Pugachev, 1999) as the mature (balanced) one in June, while in July, August and September, it was unmature (off-balance) by its characteristics. Regarding the protozoan parasites, the community in June, August and September was characterized as the mature one based on indices of parasite biomass, and as unripe one based on the number of parasite individuals; however in July, both groups of indices allowed to refer it to the unripe state. However, these unripe states are essentially different. In July, it is the result of dieing out the parasites of the past generation; in August and September, it is the result of the appearances of new generations. Therefore we recognise three states of parasite community named above. Considering the whole species composition of parasites we noted the greater difference of index values based on the parasite specimen numbers and their conventional biomass, that was in the case of the metazoan parasites only. It is particularly noticeable in the middle of the June, in the period of the formed community. This fact, together with high errors of the equations of regression and the presence of the high number of Apiosoma, points to the disturbance in the structure of component parasite community in the minnow from the Chovju River. This is easily explicable, because the Chovju River is the polluted reservoir, and pollution comes from agricultural fields, Verhny-Chov settlement, pigsties and cow-sheds. The pollution is a seasonal factor here. The most powerful pollution was noted at May-June, and then it decreased along the beginning of rains in the end of August; in September it increased again. It is important to point out that the monitoring of the metazoan parasites only allows to reveal the general dynamics of the community during the period of observation, but does not allow to catch the beginning of its destroying and developing and to notice possible disturbances in the community structure caused by pollution of reservoirs, particularly, if this pollution is a seasonal factor as in the Chovju River. Three named states of the component community of the fish parasites take place in other periods of year than this observed in the intestional parasite communities of fish helminths of the temperate climate zone. The developing of parasite communities of the intestinal helminths of the Anguilla anguilla in England (Kennedy, 1997) and of Leuciscus idus from the Rybinsk reservoir (Zhohov, 2003) starts in the beginning of summer. In May, their species diversity is minimal and in August is maximal. In conditions of the middle stream of the Vychegda River, the species diversity of parasite community associated with the minnow is maximal in June and minimal in August, when it only begins developing.     

Structure of component parasite communities in the grayling, Thymallus thymallus L. (Salmoniformes, Thymallidae), and minnow, Phoxinus phoxinus L. (Cypriniformes, Cyprinidae), from the upper reaches of the Pechora River

A comparative analysis of parasite communities in the grayling and minnow has been performed. These communities differ in the number of constituent species and in the fact that the community of the minnow is dominated by one allogenic species, whereas that of the grayling usually has two dominants, both being autogenic species. The values of species diversity indices characterizing these communities are also different. Differences between the parasite communities of these fish species reflect the position of their hosts in the hydrobiocenosis. Species prevailing in both communities are classified as specialists, which is characteristic of parasite communities of the boreal-piedmont faunal complex. Both these communities consist of three species groups distinguished by their proportions in the total biomass, which indicates that parasitic communities are structured in a certain way and that the distribution of species in them is not random.     

The parasites of Anolis lizards the northern Lesser Antilles

Summary The communities of parasitic helminths from ten species of lizards on seven islands in the Caribbean were examined to ascertain the relative importance of predictable deterministic factors and unpredicatable colonization or extinction events in determining the structure of the parasite community. A simple graphical model of community structure is used as a null model to describe the features of a community that are dependent only upon the size of the host population and features of the life histories of the constituent parasite species. This model predicts that parasite species will exhibit a nested pattern of local and global relative abundance. The observed data correspond fairly well to this pattern. The absences of individual parasite species from communities where they might be expected to be present emphasizes the role of stochastic colonization and extinction events in delineating the constituent members of the community on any island.Statistical analysis of the distribution of parasite species per host illustrates that this pattern is random in habitats where parasite species diversity is low, but decreasingly variable in habitats where more diverse parasite communities occur. Increased parasite diversity also leads to an increase in the proportion of hosts that contain mixed species infections. Comparisons of worm burdens from single and mixed species infections within individual hosts suggest that interactions between parasite species only rarely leads to reduced worm burdens.     

The functional importance of parasites in animal communities: many roles at many levels?

Past research on parasites and community ecology has focussed on two distinct levels of the overall community. First, it has been shown that parasites can have a role in structuring host communities. They can have differential effects on the different hosts that they exploit, they can directly debilitate a host that itself is a key structuring force in the community, or they can indirectly alter the phenotype of their host and change the importance of the host for the community. Second, certain parasite species can be important in shaping parasite communities. Dominant parasite species can directly compete with other parasite species inside the host and reduce their abundance to some extent, and parasites that alter host phenotype can indirectly make the host more or less suitable for other parasite species. The possibility that a parasite species simultaneously affects the structure of all levels of the overall community, i.e. the parasite community and the community of free-living animals, is never considered. Given the many direct and indirect ways in which a parasite species can modulate the abundance of other species, it is conceivable that some parasite species have functionally important roles in a community, and that their removal would change the relative composition of the whole community. An example from a soft-sediment intertidal community is used to illustrate how the subtle, indirect effects of a parasite species on non-host species can be very important to the structure of the overall community. Future community studies addressing the many potential influences of parasites will no doubt identify other functionally important parasite species that serve to maintain biodiversity.     

The occurrence of tumors in the minnow Phoxinus phoxinus (L.), their influence upon the parasite fauna, component community of parasites, and organism of the host

The occurrence of tumors, their influence upon the organism of Phoxinus phoxinus (L.), its parasite fauna, and parasite component community were investigated in the upstream of the Pechora River. According to the data obtained, tumors could occur in the fishes of every age group, but one-year (0+) or two-year (1+) old minnow is affected by tumors more frequently. The tumors lesion extensiveness ranges from 0.02 to 3 %. From 1 to 3 tumors were recorded on one fish specimen. The investigated tumors were in progressive stage (Georgiev, 2000), since the vascular ingrowth and dissemination (in few cases) of the tumors were observed. Tumors are colored in intensive-black and taupe. The taupe tumors usually have a compact capsule at its peripheries, which isolates affected tissue from muscle fibers. In the intensive-black tumors the invasion of tumor cells to the adjacent transversal striated musculature is observed. Distinct symptoms of necrosis are revealed in all slides of the new growths. Blood vessels are formed in most tumors, and the blood flow is recorded before the completion of the vessels forming, that apparently supplies the tumors feeding. Metastases in different organs revealed in several minnow specimens. Tumor affected individuals of the minnow has parasite species complex practically identical (by species list and quantity) with the same of the even-aged unaffected fishes. However, the parasite component communities of the affected individuals are characterized by 4 groups of species, while the parasite component communities of the intact individuals--by 3 groups. The parasite communities of affected and unaffected one-year fishes are similar by the number of the groups of species, but differ in the number of species.     

Dependence of the structure of component parasite communities on host age

Dependence of the structure of component parasite communities on host age is studied by the example of parasite communities in minnow and grayling from the North Dvina and Pechora rivers basins. Parasite communities from immature host groups are revealed to be different from those in mature fishes by lesser number of parasite individuals and biomass, number of groups discriminated by the ratio of biomasses, and frequently by lesser number of species. Indices of diversity describing parasite communities from hosts of different ages are nearly always the same in the area examined. This observation needs in verification because values of the indices characterizing parasite communities from fishes of different ages are not equal in the parasite communities from grayling of different age from the Pinega river and minnow from the Chovju river (Dorovskikh, 2002).     

Linking community assembly and structure across scales in a wild mouse parasite community

Understanding what processes drive community structure is fundamental to ecology. Many wild animals are simultaneously infected by multiple parasite species, so host–parasite communities can be valuable tools for investigating connections between community structures at multiple scales, as each host can be considered a replicate parasite community. Like free‐living communities, within‐host–parasite communities are hierarchical; ecological interactions between hosts and parasites can occur at multiple scales (e.g., host community, host population, parasite community within the host), therefore, both extrinsic and intrinsic processes can determine parasite community structure. We combine analyses of community structure and assembly at both the host population and individual scales using extensive datasets on wild wood mice (Apodemus sylvaticus) and their parasite community. An analysis of parasite community nestedness at the host population scale provided predictions about the order of infection at the individual scale, which were then tested using parasite community assembly data from individual hosts from the same populations. Nestedness analyses revealed parasite communities were significantly more structured than random. However, observed nestedness did not differ from null models in which parasite species abundance was kept constant. We did not find consistency between observed community structure at the host population scale and within‐host order of infection. Multi‐state Markov models of parasite community assembly showed that a host's likelihood of infection with one parasite did not consistently follow previous infection by a different parasite species, suggesting there is not a deterministic order of infection among the species we investigated in wild wood mice. Our results demonstrate that patterns at one scale (i.e., host population) do not reliably predict processes at another scale (i.e., individual host), and that neutral or stochastic processes may be driving the patterns of nestedness observed in these communities. We suggest that experimental approaches that manipulate parasite communities are needed to better link processes at multiple ecological scales.     

Nonhost species reduce parasite infection in a focal host species within experimental fish communities

The dilution effect describes the negative association between host biodiversity and the risk of infectious disease. Tests designed to understand the relative roles of host species richness, host species identity, and rates of exposure within experimental host communities would help resolve ongoing contention regarding the importance and generality of dilution effects. We exposed fathead minnows to infective larvae of the trematode, Ornithodiplostomum ptychocheilus in minnow‐only containers and in mixed containers that held 1–3 other species of fish. Parasite infection was estimated as the number of encysted worms (i.e., brainworms) present in minnows following exposure. The results of exposure trials showed that nonminnow fish species were incompatible with O. ptychocheilus larvae. There was no reduction in mean brainworm counts in minnows in mixed containers with brook sticklebacks or longnose dace. In contrast, brainworm counts in minnows declined by 51% and 27% in mesocosms and aquaria, respectively, when they co‐occurred with emerald shiners. Dilution within minnow + shiner containers may arise from shiner‐induced alterations in minnow or parasite behaviors that reduced encounter rates between minnows and parasite larvae. Alternatively, shiners may act as parasite sinks for parasite larvae. These results highlight the role of host species identity in the dilution effect. Our results also emphasize the complex and idiosyncratic effects of host community composition on rates of parasite infection within contemporary host communities that contain combinations of introduced and native species.     

The role of the European bitterling (<Emphasis Type="Italic">Rhodeus amarus,</Emphasis> Cyprinidae) in parasite accumulation and transmission in riverine ecosystems

In aquatic ecosystems, fish play a key role in parasite accumulation and transmission to predacious animals. In the present study, realized on seven populations of a small cyprinid fish species, the European bitterling Rhodeus amarus, we investigated (1) the role of the European bitterling as a potential intermediate or paratenic host, (2) the ability of the fish to accumulate parasites with similar final host group, and (3) its significance as a potential source of parasite infection in the ecosystem in respect to habitat characteristics. A total of 36 parasite species were recorded; 31 species (90% of all parasite specimens) were classified as endoparasites. Most of the endoparasites were found in the larval life stage, using bitterling as an intermediate or paratenic host. In particular, parasite community structure showed significantly higher proportions of allogenic parasites in comparison with autogenic. The supposed co-occurrence of parasite species with identical final host groups showed only a weak association. The adjacent reservoir areas were a significant determinant of both the total and infracommunity parasite species richness and for the mean parasite abundance. No relationship between the distance of sampling site from the adjacent reservoir and parasite community characteristics was found. As a small-sized fish with a wide distribution range and high local abundances, the European bitterling can represent a natural prey for a wide range of piscivorous predators. Due to its susceptibility to the number of larval endoparasites, this fish species may therefore fulfill the role as important transmitter of parasites to their final hosts.     

Nestedness in assemblages of gyrodactylids (Monogenea: Gyrodactylidea) parasitising two species of cyprinid--with reference to generalists and specialists

The structure of gyrodactylid assemblages in individual fishes of two species of cyprinid was determined. A total of 100 specimens of minnow, Phoxinus phoxinus, and 137 specimens of roach, Rutilus rutilus, were investigated for presence of gyrodactylids. Host specificity, specialists vs. generalists, was noted in each host fish. A nested pattern was recorded in parasite assemblages of minnow, the host with a dominant number of specialist gyrodactylids. A non-nested pattern was observed in parasite assemblages of roach, the host with a dominant number of generalist gyrodactylids. The host specificity appears to be a meaningful factor that determines the pattern of gyrodactylid assemblages of both fish hosts.     

Halfway up the trophic chain: development of parasite communities in the sparid fish Boops boops

We examined the patterns of composition and structure of parasite communities in the Mediterranean sparid fish Boops boops along a gradient of fish sizes, using a large sample from a single population. We tested the hypothesis that species forming the core of the bogue parasite fauna (i.e. species which have a wide geographical range and are responsible for recognizable community structure) appear early in the fish ontogeny. The sequential community development observed supported the prediction that core species appear in the fish population earlier than rare and stochastic species. There was also a strong correlation between the order of 'arrival' of the species and their overall prevalence. Six key species were responsible for recognizable community structure across size/age cohorts; the addition to this baseline community of key parasite species resulted in a nested structure that is linked to differential species abundance rather than fish size. Information on the life-cycles, distribution and host range of the parasites is used to explain the observed patterns of parasite community structure. We conclude that the small mouth size of B. boops coupled with suction feeding may provide a setting for passive sampling as a mechanism leading to non-random parasite community structure.     

Parasite communities and a fish spawn

High values of dominance index, low values of evenness and Shannon index are characteristic of component parasite communities of prespawning (Prosopium cylindraceum) and spawn migratory fishes (Coregonus autumnalis, Oncorhynchus nerka). Autogenic specialists are dominant in the component parasite communities of C. autumnalis. The component parasite communities of P. cylindraceum and O. nerka are dominant in a content of generalist species. The O. nerka parasite communities are communities "sentenced to death". Low values of dominance index, high values of evenness abd Shannon index are peculiar to component parasite communities of prespawning and spawning cyprinid fishes (Phoxinus phoxinus, Oreoleuciscus humilis). Autogenic specialists are dominant. Increase of dominance index and decrease of two other indexes characterize the postspawning period. The same tendency characterises infracommunities. Thus, the component parasite communities respond differently to the fish spawn of the cyprinid and coregonid/salmonid fishes. Similarity is in the dominance of autogenic specialists in one case only (C. autumnalis). These differences are defined by the mode of fish stock formation for spawn. The cyprinids congregate for spawning and move apart for foraging and vice versa is observed in the coregonids and salmonids. Autogenic specialists dominance seems to be the important adaptation to reduce a negative effect to host during spawning. Bush and Kennedy in 1994 established that "parasites live in patches (host individuals) and fragments (host populations)". They consider the host fragmentation as "hedging your bets against extinction" due to frequency and magnitude anthropogenic factors, which increase fragmenting of host populations. This conclusion was made for a species level. From the other hand the fragmentation is a natural feature for a single host population too. Such fragmentation is a host population structure. The role of fragmentation is obvious from the data on component parasite communities during fish spawn. The fragmentation decreases in the cyprinids and increases in the salmonids that leads to the growing of the cyprinid component parasite communities diversity and to declining the salmonid component parasite communities diversity. Nevertheless the role of host population structure in a component parsite community structure is not obvious, because parasites are able or not able to "recognise" different host subpopulation groups. It is well known from data on parasite species population biology. Such recognizable subpopulation groups or groups can be a "real fragment" for the parasite community. The question is what parameters could be used for this purpose on a component community level. Host population age structure can be used as an example, because the age groups are one of the invariable population characters. Value of Shannon index for component parasite communities of spawn migratory O. nerka (5+) is similar to that of fishes of 1+ age. Difference is statistically insignificant. It is insignificant between the parasite communities of 2+ and 3+ age groups too. Fishes of these two groups could be defined as a real united fragment. It spite of similarity between the fishes of 5+ age group and fish of 1+ age group they are not united fragment. The parasite community of 1+ age fishes is not stabilized yet and one of 5+ age is a community "sentenced to death". Thus the structuring of O. nerka freshwater parasite communities are defined by 3 real host age fragments: 1+ age group, 2 and 3+ age group, 4+ age group. It looks as that Shannon index is suitable parameter to study a parasite communities structure.     

The influence of biomanipulation on fish community development in a southeastern United States cooling reservoir

L Lake, a reactor cooling reservoir in South Carolina, USA was managed after filling to promote the development of healthy ecological communities similar to those in mature regional cooling reservoirs. Two types of biomanipulation were undertaken to achieve this goal, the introduction of typical southeastern US reservoir fishes (bluegill and largemouth bass) and artificial planting of native aquatic macrophytes. Fish assemblages were monitored by electrofishing from reservoir filling in 1986 until 1998. Multivariate analysis divided the fish samples into five sequential periods resulting from species replacements and additions. Small species that colonized L Lake from a feeder stream predominated in the first period but were mostly eliminated, as bluegill, largemouth bass, and other lentic species increased in the second period. A rapid increase in threadfin shad abundance characterized the third period, and small littoral zone and phytophilous fishes increased during the fourth and fifth periods coincident with the proliferation of aquatic macrophytes. Analysis of Bray-Curtis similarities and the species accumulation rate indicated that the rate of fish community change decreased with time and that fish community structure changed little during the last several years of the study. By the end of the study, community structure was similar to that in a nearby cooling reservoir that supported diverse and resilient biota. Biomanipulation contributed to the rapid establishment of lentic species and later increases in small littoral and phytophilous species suggesting that biomanipulation may be useful in accelerating fish community development in new cooling reservoirs.     

Temperature and multiple parasites combine to alter host community structure

Predicting the effects of climate change requires understanding complex interactions among multiple abiotic and biotic factors. By influencing key interactions among host species, parasites can affect community and ecosystem structuring. Yet, our understanding of how multiple parasites and abiotic factors interact to alter ecosystem structure remains limited. To empirically test the role of temperature variation and parasites in shaping communities, we used a multigenerational mesocosm experiment composed of four sympatric freshwater crustacean species (isopods and amphipods) that share up to four parasite species. Mesocosms were assigned to one of four different treatments with contrasting seasonal temperatures (normal and elevated) and parasite exposure levels (continuous and arrested (presence or absence of parasite larvae in mesocosm)). We found that parasite exposure and water temperature had interactive effects on the host community. Continuous exposure to parasites altered the community structure and differences in water temperature altered species abundance. The abundance of the amphipod Paracalliope fluviatilis decreased substantially when experiencing continuous parasite exposure and elevated water temperatures. Elevated temperatures also led to parasite-induced mortality in another amphipod host, Paracorophium excavatum. Contrastingly, isopod hosts were affected much less, suggesting increasing temperatures in conjunction with higher parasite exposure might increase their relative abundance in the community. Changes in invertebrate host populations have implications for other species such as fish and birds that consume crustaceans as well as having impacts on ecosystem processes, such as aquatic primary production and nutrient cycling. In light of climate change predictions, parasite exposure and rise in average temperatures may have substantial impacts on communities and ecosystems, altering ecosystem structure and dynamics.     

Upstream effects of a reservoir on fish assemblages 45 years following impoundment

Fish assemblage structure, rarefied species richness, species diversity and evenness of assemblages upstream of a reservoir in Oklahoma, U.S.A., were compared pre and post‐impoundment as well as in contemporary collections from streams above and below the reservoir. There were significant shifts in assemblage structure between historical and contemporary collections above the reservoir but not between contemporary assemblages above and below the impoundment. Indicator species analysis revealed that the sand shiner Notropis stramineus and fathead minnow Pimephales promelas have declined, whereas largemouth bass Micropterus salmoides and western mosquitofish Gambusia affinis have increased in relative abundance in assemblages upstream of the impoundment. Species richness was lower in contemporary assemblages compared with historical assemblages. Furthermore, contemporary assemblages below the dam had lower species richness, diversity and evenness compared with contemporary collections above the dam. These results highlight the spatial and temporal extent of reservoirs altering fish assemblages upstream of impoundments.     

High intensity and prevalence of two species of trematode metacercariae in the fathead minnow (Pimephales promelas) with no compromise of minnow anti-predator competence

Opportunity for parasites to manipulate host behavioral phenotype may be influenced by several factors, including the host ecology and the presence of cohabiting parasites in the same host. Metacercariae of Ornithodiplostomum ptychocheilus and "black spot" Crassiphiala bulboglossa have similar life cycles. Each parasite uses a littoral snail as a first intermediate host, fathead minnows as a second intermediate host, and a piscivorous bird as a final host. Metacercariae of black spot encyst in the dermal and epidermal tissues, while metacercariae of O. ptychocheilus encyst on the brain over a region that coordinates optomotor responses. Because of site differences within the host, we predicted that O. ptychocheilus metacercariae might manipulate the behavioral phenotype of minnows to facilitate transmission to the final host, but metacercariae of black spot would not. In our study population, prevalence was 100% for O. ptychocheilus , with an overall median intensity of 105 metacercariae per minnow. Prevalence of black spot was 60%, with a median abundance and intensity of 12 and 20 metacercariae per minnow for the overall sample and for infected fish, respectively. Minnows accumulated both parasites over time, producing significant correlations between intensity and minnow body length and between intensities of the 2 parasites. Minnows infected with black spot had on average twice as many O. ptychocheilus metacercariae as similar-sized minnows without any black spot cercariae. We found no correlation between body condition of minnows and intensity for either parasite. We measured 2 aspects of anti-predator competence to test for effects linked to parasite intensity. We found no correlation between intensity of either species of parasite and latency to behavioral response to attack from a mechanical model heron, nor was there any effect of parasite intensity on a measure of shoaling affinity. The absence of any detectable effect of metacercariae on anti-predator competence in minnows may reflect selection against parasite pathology from predation by non-hosts of the parasites and overwinter mortality due to low dissolved oxygen.     

Relative importance of host environment,transmission potential and host phylogeny to the structure of parasite metacommunities

Identification of mechanisms that shape parasite community and metacommunity structures have important implications to host health, disease transmission, and the understanding of community assembly in general. Using a long‐term dataset on parasites from desert rodents, we examined the relative contributions of host traits that represent important aspects of parasite environment, transmission probability between host species, and host phylogeny to the structure of a parasite metacommunity as well as for taxonomically restricted parasite metacommunities (coccidians, ectoparasites and helminths). This was done using a combination of metacommunity analysis and variance partitioning based on canonical correspondence analysis. Coccidian and ectoparasite metacommunities did not exhibit coherent structure. In contrast, helminths and the full parasite metacommunity had Clementsian and quasi‐Clementsian structure, respectively, indicating that parasite species distributions for these metacommunities were compartmentalized along a dominant gradient. Variance decomposition indicated that characteristics associated with the host environment consistently explained more variation than did host traits associated with transmission opportunities or host phylogeny, indicating that the host environment is primary in shaping parasite species distributions among host species. Moreover, the importance of different types of host traits in structuring parasite metacommunities was consistent among taxonomic groups (i.e. full metacommunity, coccidians, and helminths) despite manifest differences in emergent structures (i.e. Clementsian, quasi‐Clementsian, and random) that arose in response to variation in host environment.