Robert Poulin

..Our results thus indicate that the infracommunity of larval helminths in their intermediate host is interactive and that any density-dependent effect in the intermediate host may have lasting effects on individual parasite fitness...

..Still, these results suggest that host specificity may have tended to decrease in many flea lineages, a process that could have been driven by the benefits of exploiting a wide range of host species...

..The time has come to transform fish parasite ecology from a mostly descriptive discipline into a predictive science, capable of integrating complex ecological data to generate forecasts about the future state of host-parasite systems...

..These findings suggest that strong interactions may lead to greater evenness in the abundance of species, and that numerical dominance is more likely to result from interspecific differences in recruitment rates...

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..The fact that the evolution of the body plan is more conservative than that of body size suggests that the range of morphologies that can evolve in trematodes is constrained...

..The use of the index in comparative studies may help in determining whether interactive helminth communities are, as widely believed, more common in endothermic vertebrate hosts than in fish hosts...

..These findings indicate that particular species characters may be evolutionary drivers of diversity, whose effects could also apply in other taxa...

..If the number of parasite species exploiting a host population is not regulated by processes arising from within the parasite community, external factors such as host characteristics may be the main determinants of parasite diversity...

..The present findings suggest that the design of experimental infection studies requires greater consideration if their results are to yield useful biological insights...

..It also summarizes the first findings to emerge from network analyses of host-parasite interactions and identifies promising future directions made possible by this approach...

..These relationships also suggest that adult size is to some extent determined by cystacanth size, and that the characteristics of the definitive host are not the sole determinants of parasite life history traits...

..We recommend the use of our new index in future comparative studies of host specificity, in particular when the focus is on the evolutionary history of parasites and of their past colonizations of host lineages...

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..Nematode body size may thus determine the abundance achieved by a species but not how many species can coexist; the limiting similarity between coexisting species must depend on other biological traits...

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..This has important but previously overlooked implications for the interpretation of correlation coefficients, and the detection of competition in natural parasite communities...

..This conclusion supports the view that the biological features of parasite species can potentially override local environmental conditions in driving parasite population dynamics...

..Our results demonstrate that the parasite species known at any given point in time are not a random subset of existing species, but rather a biased subset with respect to the parasites' biological properties...

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..75, suggests that parasites are not like host tissues: they are able to appropriate more host resources than expected from metabolically derived host growth rates...

..e. the parasite community level, appear highly contingent and far from universal. The general laws uncovered to date are proving valuable, as they offer glimpses of the underlying processes shaping parasite ecology and diversity...

..Although the results are based on a limited number of parasite taxa, they suggest that parasites may be opportunistic in their colonization of new hosts, and not severely constrained by evolutionary baggage...

..Here, the prospects offered by both approaches, as well as their limitations, are highlighted...

..Interaction frequency may be a key determinant of specialisation and abundance in host-parasite systems...

..truncatus than the mass of any other species taken on its own. These results illustrate the importance of considering helminth interactions and helminth growth in a natural setting...

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..The loss of expertize in parasite taxonomy happening worldwide is one possible explanation. This downward trend needs to be reversed if we are to monitor new parasite occurrences in the face of environmental changes...

..The present evidence suggests that the role of species interactions in helminth community structure is often negligible, but that it must always be evaluated on a case-by-case basis...

..These results show that different parasite species do not use cockles in a random fashion, and that not all patterns of host use are consistent with shared or conflicting interests among parasites...

..The continuum between nestedness and anti-nestedness also has implications for recent models of species coexistence in communities...

..A better integration of ecological and historical (or phylogenetic) approaches to the study of parasite diversity should make this objective possible...

..Instead, it suggests that parasites may be colonising host species showing low levels of genetic variation with greater success than genetically more variable host species...

..These results have several possible explanations, but tend to suggest biases with regard to what results are published through time as accepted paradigms changed...

..These examples demonstrate the pervasive influence of distances among host populations on their parasite communities, and the need to properly control for them in statistical analyses...

..Future community studies addressing the many potential influences of parasites will no doubt identify other functionally important parasite species that serve to maintain biodiversity...

..Here, Robert Poulin and Frederic Thomas review the types of host traits that are modified by parasites, then explore some of the ..

..The general trend observed in non-salmonid fish suggests that parasite colonization and speciation may have been facilitated in some fish species, but not in others...

..Severe space constraints and a greater diversity of small niches may only allow the diversification of small endoparasites, whereas ectoparasite body sizes may face less severe limitations...

..The similarity in life-history traits among members of given clades suggests that phylogenetic constraints may have acted to limit or mask any adaptive changes expected from changes in host-related or environmental conditions...

..The meta-analysis suggests that male hosts harbour not only more helminths than females, but also slightly larger ones...

..Thus, nestedness in parasite communities may result from processes somewhat different from those generating nested patterns in free-living communities...

..The results suggest that assemblages of larval helminth parasites in fish are not random collections of locally available species, but rather structured packets of larval parasites that travel together along common transmission routes...

..There may be some general, large-scale processes acting to structure helminth communities, but local or seasonal influences can often either mask their action, or play more important roles themselves...

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..The main consequence of this phenomenon is that worm sizes in the mermithid population are more homogeneous than they would be if intraspecific competition had stronger effects on worm growth...

..The results show that similarity in species composition decreases, though weakly, with increasing distance in the same manner in phylogenetic space as it does in geographical space...

..The study of shorter life cycles offers an opportunity to understand the forces shaping the evolution of life cycles in general...

..The phylogenetic analytical framework adopted here should allow these questions to be tackled once the necessary data become available...

..These results suggest that there is an increasing gap in the quantity and general importance of the research carried out on different helminth taxa...

..The available data suggest that current estimates of helminth diversity may need to be doubled (tripled for trematodes) to better reflect extant diversity...

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..In this system, the site of encystment within the fish host both promotes and constrains the adoption of a facultative, truncated life-cycle by the parasite...

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..Host spawning events are likely to be an avenue of egg dispersal for this progenetic species, with the adoption of progenesis being conditional on whether or not the parasite can benefit from fish spawning...

..The indices presented here capture essential features of resource use in parasite communities, and can be useful tools for comparative analyses...

..The presence of a large number of infected snails and tidal mixing of cercariae prior to infection results in crabs potentially harbouring hundreds of parasite genotypes despite the crabs' territorial behaviour...

..Our results suggest that the dynamics of competition between coinfecting parasites, although influenced by numerous external factors, is also modulated by genetic relatedness among parasites...

..in A. crassa. Overall, the different parasite species make different use of available crustacean intermediate hosts and possibly contribute to intertidal community structure...

..These results show that the life history strategy adopted by a parasite may be influenced by other parasites sharing the same host...

..The results also support the role of the second intermediate host as an accumulator of genetic diversity in the trematode life cycle...

..Results indicate that these two species are ecological equivalents, and their combined numbers determine how the cockle population is affected...

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..Overall, the results suggest that, at least for Microphallus, local infection levels depend on local intermediate host densities...

..The results suggest that the anemone-cockle symbiosis is a non-obligate mutualistic relationship in which the former is provided with a suitable substrate for attachment whereas the latter obtains protection against parasitic infections...

..novizealandiae infected with M. novaezealandensis is most likely due to pathology caused by the parasite rather than a case of active, and adaptive, behavioural manipulation...

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..Possible alternative reasons for the pattern of positive association between the gymnophallid and the echinostomes are proposed...

..Our results shed light on the conditions that may favour switching among intermediate hosts in digeneans, and on the presence/absence of host specificity in these parasites...

..This method should be extremely useful for experimental studies using trematode-host systems as models for addressing a range of ecological and evolutionary questions...

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..These findings illustrate the ways in which phylogenetically based comparative methods can contribute to biogeographic research...

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..liliana. However, due to the low infection intensity and population density of M. liliana, its overall impact as a sink for echinostome populations in the ecosystem is probably negligible...

..Both these feeding behaviours of birds are known to occur in the field...

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..Hence, trout presence may instead reduce parasite burdens in galaxias by either reducing galaxias density or by altering galaxias foraging behaviour...

..These findings highlight the often unrecognised plasticity in parasite developmental and transmission strategies...

..This review uses several well-known pathogens to demonstrate how host manipulation by parasites is potentially important in epidemiology...

..Consequently, a trade-off between size and numbers is possibly imposed by external forces influencing host size, hence limiting physical space or other resources available to the parasites...

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..The combination of aggregation and intensity-dependent growth generates inequalities in sizes among metacercariae that will be passed on to adult worm populations in definitive hosts...

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..It is possible that the parasite's natural environment contains so many layers of heterogeneity that C. parvum does not possess the ability to adjust its life-history strategy to accurately match the current conditions...

..Inbreeding depression is unlikely to be a factor acting on the maintenance of the normal three-host life cycle, and thus out-crossing, in C. parvum populations...

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..Thus, both active hitch-hiking and incidental facilitation lead to non-random infection patterns in this parasite community...

..The results suggest that environmental gradients like salinity can be strong driving forces behind patterns of distance decay in parasite communities of fishes...

..Acanthobothrium species have evolved a generalized mode of attachment that is successful in maintaining their position on various intestinal mucosal topographies across a variety of hosts exploiting different food resources...

..Why facultative progenesis is not more widespread remains a mystery...

..Few known examples satisfy more than two of the above criteria, and, in general, the adaptive function of changes in host behaviour following infection is in need of more solid proof...

..These results show that parasites with complex developmental routes have transmission strategies and perception abilities that are more sophisticated than previously thought...

..Possible explanations for this spatial segregation of the species include sampling artefacts, local adaptation by first intermediate hosts, environmental conditions, and site fidelity of the definitive hosts...

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