Food-web-based comparison of the drivers of helminth parasite species richness in coastal fish and bird definitive hosts

Studies on the factors determining parasite richness in hosts are typically performedusing data compiled for various sets of species from disparate habitats. However, parasite transmissionis embedded within local trophic networks, and proper comparisons among host speciesof the drivers of parasite richness should ideally be conducted among hosts belonging to the samelocal network. Here, we used data from 6 well-resolved coastal food webs that include parasites toinvestigate patterns and drivers of species richness of trophically transmitted helminths in coastalfish and bird definitive hosts. We first investigated whether previous notions that birds harbourmore trophically transmitted parasite species than fish hold true for food-web-based comparisons;then we investigated the roles of host prey range, trophic level and body size in driving parasiterichness patterns in coastal birds and fish. Our analyses indicated that bird hosts, on average, harbouredhigher parasite richness than fish hosts. While there was no consistent driver of parasiterichness at the level of entire food webs, host prey range and host trophic level were positively correlatedwith parasite richness in birds within individual food webs. For fish hosts, the effect of hostprey range was less consistent and trophic level had no effect on parasite richness. Host body sizedid not affect parasite richness for either host type. These results suggest that host prey range andtrophic level seem to be more consistent drivers of parasite richness for coastal bird than for fishhosts

Inventory and comparison of abundance of parasitic copepods on fish hosts in the western Wadden Sea (North Sea) between 1968 and 2010

A conspicuous part of the parasite fauna of marine fish are ectoparasites, which attach mainly to the fins or gills. The abundant copepods have received much interest due to their negative effects on hosts. However, for many localities the copepod fauna of fish is still poorly known, and we know little about their temporal stability as long-term observations are largely absent. Our study provides the first inventory of ectoparasitic copepods on fish from the western Wadden Sea (North Sea) based on field data from 1968 and 2010 and additional unpublished notes. In total, 47 copepod parasite species have been recorded on 52 fish host species to date. For two copepod species parasitizing the European flounder (Platichthys flesus), a quantitative comparison of infection levels between 1968 and 2010 was possible. Whereas Acanthochondria cornuta did not show a change in the relationship between host size and infection levels, Lepeophtheirus pectoralis shifted towards the infection of smaller hosts, with higher infection levels in 2010 compared to 1968. These differences probably reflect the biology of the species and the observed decrease in abundance and size of flounders during the last decades. The skin-infecting L. pectoralis can probably compensate for dwindling host abundance by infecting smaller fish and increasing its abundance per given host size. In contrast, the gill cavity inhabiting A. cornuta probably faces a spatial constraint (fixed number of gill arches), thus limiting its abundance and setting a minimum for the host size necessary for infections

Trematode prevalence-occupancy relationships on regional and continental spatial scales in marine gastropod hosts

The positive inter-specific relationship between local abundance and large-scale spatial occupancy is one of the most universal patterns in the distribution of species. However, evidence for the validity of this relationship in the marine realm is still scarce, especially for parasites. Using data from published studies, we investigated this relationship in trematode parasites infecting several marine gastropod species. On a regional spatial scale (<100 km between any pair of sites), we found a positive relationship between mean local prevalence (percentage of infected individuals in a population) and large-scale site occupancy among trematode species in all 4 gastropod host species investigated (Littorina obtusata, L. saxatilis, Hydrobia ventrosa, Ilyanassa obsoleta), although this was not significant in the case of L. saxatilis. Similar positive relationships were observed on a continental scale (> 1000 km between the most distant sites) in 2 host species (L. littorea, H. ulvae). Further analyses pointed to the role of dispersal by the definitive hosts in shaping these prevalence-occupancy relationships as we found a significant interaction between definitive host type and mean local prevalence affecting the spatial occupancy of the trematodes infecting H. ulvae. While trematode species that use highly dispersive birds as definitive hosts exhibited a significant positive relationship, the ones that use less dispersive fish did not. Our results indicate that a positive relationship between local abundance and large-scale distribution also holds true for marine parasites, and they suggest a strong role of definitive host dispersal in linking local epidemiological infection patterns of parasites with their large-scale biogeographic distributions

The most vagile host as the main determinant of population connectivity in marine macroparasites

Although molecular ecology of macroparasites is still in its infancy, general patterns are beginning to emerge, e.g. that the most vagile host in a complex life cycle is the main determinantof the population genetic structure of their parasites. This insight stems from the observation that populations of parasites with only freshwater hosts are more structured than those with terrestrial or airborne hosts. Until now, the same has not been tested for marine systems, where, in theory, a fully marine life cycle might sustain high dispersal rates because of the absence of Obvious physical barriers in the sea. Here, we tested whether a marine trematode parasite that utilises migratory birds exhibited weaker population genetic structure than those whose life cycle utilises marine fish as the vagile host. Part of the mitochondrial cytochrome c oxidase 1 (COI) gene wassequenced from individual sporocysts from populations along the Atlantic coast of Europe and North Africa. Strong population structure (Φ-ST = 0.25, p < 0.0001) was found in the fully marinetrematode Bucephalus minimus (hosted by fish), while no significant structure (Φ-ST = 0.015, p = 0.19257) was detected in Gymnophallus choledochus (hosted by birds). However, demographicmodels indicate recent colonisation rather than high dispersal as an alternative explanation of the low levels of structure observed in G. choledochus. Our study is the first to identify significant genetic population structure in a marine autogenic parasite, suggesting that connectivity between populations of marine parasites can be limited despite the general potential for high dispersal of their hosts in the marine environment

MINIMUM CONTRAST ESTIMATION FOR DISCRETELY OBSERVED DIFFUSION PROCESSES WITH SMALL DISPERSION PARAMETER

The parametric estimation of both drift and diffusion coefficient parameters for $d$-dimensional diffusion processes with small dispersion parameter $\varepsilon$ is stated when the data are discretely observed at equidistant time points $k/n$, $k = 0,1, cdots, n$. Using the contrast function based on a Gaussian approximation to the transition density, we present asymptotic properties for the minimum contrast estimator as $\varepsilon$ tends to $0$ and $n$ tends to $infty$ simultaneously

Parasites as prey

Parasites are usually considered to use their hosts as a resource for energy. However, there is increasing awareness that parasites can also become a resource themselves and serve as prey for other organisms. Here we describe various types of predation in which parasites act as prey for other organisms: (1) predation of nonhosts on infected hosts (concomitant predation), (2) predation on free‐living parasite life cycle stages, (3) predation on ectoparasites in form of grooming or cleaning and (4) predation or hyperparasitism by other parasites. In many cases, these types of predation significantly reduce the numbers of parasites and thus affect parasite population dynamics. In contrast, predation on parasites is often beneficial for the hosts as they are released from parasite burden. Finally, when parasites act as prey they may contribute to the nonhost predator's diet, in some cases constituting a significant proportion of energy intake

Ecology of parasites in mudflat ecosystems

Mudflats are not only home to large numbers of bivalves, polychaetes,crustaceans, fish and birds, but also to diverse communities of parasites. In thischapter, we illustrate and explore how the resulting parasite-host interactions canaffect host populations, communities and food webs in mudflat ecosystems, equallingin importance the effects resulting from other species interactions, such as predation and competition. We first give an overview of the distribution and ecologyof typical parasites occurring in mudflat ecosystems. Then we illustrate the mainabiotic and biotic drivers of parasite infection levels in mudflat hosts. Following this,we conceptualise and illustrate the many direct and indirect effects of parasite-hostinteractions on host populations, communities and food webs in mudflat ecosystems.Finally, we highlight the potential impact of ongoing global changes such asincreasing temperature and species introductions on parasite-host interactions inmudflat ecosystems. With this condensed overview of the presence and ecologicalrole of parasites in mudflat ecosystems, we hope to increase the appreciation of themanifold ecological effects of parasite-host interactions on host populations, communitiesand food webs of mudflat ecosystems, and to spark further research in this fiel

Phylogeny determines the role of helminth parasites in intertidal food webs

1.Parasites affect interactions among species in food webs and should be considered in any analysis of the structure, dynamics or resilience of trophic networks.2.However, the roles of individual parasite species, such as their importance as connectors within the network, and what factors determine these roles, are yet to be investigated. Here, we test the hypotheses that the species roles of trematode, cestode and nematode parasites in aquatic food webs are influenced by the type of definitive host they use, and also determined by their phylogenetic affiliations.3.We quantified the network role of 189 helminth species from six highly resolved intertidal food webs. We focused on four measures of centrality (node degree, closeness centrality, betweenness centrality and eigenvalue centrality), which characterize each parasite's position within the web, and on relative connectedness of a parasite species to taxa in its own module vs. other modules of the web (within-module degree and participation coefficient).4.All six food webs displayed a significant modular structure, that is, they consisted of subsets of species interacting mostly with each other and less with species from other subsets. We demonstrated that the parasites themselves are not generating this modularity, though they contribute to intermodule connectivity.5.Mixed-effects models revealed only a modest influence of the type of definitive host used (bird or fish) and of the web of origin on the different measures of parasite species roles. In contrast, the taxonomic affiliations of the parasites, included in the models as nested random factors, accounted for 37–93% of the total variance, depending on the measure of species role.6.Our findings indicate that parasites are important intermodule connectors and thus contribute to web cohesion. We also uncover a very strong phylogenetic signal in parasite species roles, suggesting that the role of any parasite species in a food web, including new invasive species, is to some extent predictable based solely on its taxonomic affiliations

ジャン・パウルと自我の構造

ジャン・パウルの天才概念 ジャン・パウルの自我概

The comparative ecology and biogeography of parasites

Comparative ecology uses interspecific relationships among traits, while accounting for the phylogenetic non-independence of species, to uncover general evolutionary processes. Applied to biogeographic questions, it can be a powerful tool to explain the spatial distribution of organisms. Here, we review how comparative methods can elucidate biogeographic patterns and processes, using analyses of distributional data on parasites (fleas and helminths) as case studies. Methods exist to detect phylogenetic signals, i.e. the degree of phylogenetic dependence of a given character, and either to control for these signals in statistical analyses of interspecific data, or to measure their contribution to variance. Parasite-host interactions present a special case, as a given trait may be a parasite trait, a host trait or a property of the coevolved association rather than of one participant only. For some analyses, it is therefore necessary to correct simultaneously for both parasite phylogeny and host phylogeny, or to evaluate which has the greatest influence on trait expression. Using comparative approaches, we show that two fundamental properties of parasites, their niche breadth, i.e. host specificity, and the nature of their life cycle, can explain interspecific and latitudinal variation in the sizes of their geographical ranges, or rates of distance decay in the similarity of parasite communities. These findings illustrate the ways in which phylogenetically based comparative methods can contribute to biogeographic research