Understanding trophic interactions in host-parasite associations using stable isotopes of carbon and nitrogen

Abstract

BackgroundStable isotope analysis of carbon and nitrogen can deliver insights into trophic interactions between organisms. While many studies on free-living organisms are available, the number of those focusing on trophic interactions between hosts and their associated parasites still remains scarce. In some cases information about taxa (e.g. acanthocephalans) is completely missing. Additionally, available data revealed different and occasionally contrasting patterns, depending on the parasite’s taxonomic position and its degree of development, which is most probably determined by its feeding strategy (absorption of nutrients through the tegument versus active feeding) and its localization in the host.MethodsUsing stable isotope analysis of carbon and nitrogen we provided first data on the trophic position of an acanthocephalan species with respect to its fish host. Barbels (Barbus barbus) infected only with adult acanthocephalans Pomphorhynchus laevis as well as fish co-infected with the larval (L4) nematodes Eustrongylides sp. from host body cavity were investigated in order to determine the factors shaping host-parasite trophic interactions. Fish were collected in different seasons, to study also potential isotopic shifts over time, whereas barbels with single infection were obtained in summer and co-infected ones in autumn.ResultsAcanthocephalans as absorptive feeders showed lower isotope discrimination values of δ 15N than the fish host. Results obtained for the acanthocephalans were in line with other parasitic taxa (e.g. cestodes), which exhibit a similar feeding strategy. We assumed that they feed mainly on metabolites, which were reprocessed by the host and are therefore isotopically lighter. In contrast, the nematodes were enriched in the heavier isotope δ 15N with respect to their host and the acanthocephalans, respectively. As active feeders they feed on tissues and blood in the body cavity of the host and thus showed isotope discrimination patterns resembling those of predators. We also observed seasonal differences in the isotope signatures of fish tissues and acanthocephalans, which were attributed to changes in food composition of the host and to seasonality in the transmission and development of acanthocephalans.ConclusionsThis study provided first data on trophic interaction between an acanthocephalan species and its associated host, which support the tendency already described for other taxa with similar nutrition strategy (e.g. cestodes). Actively feeding taxa such as larval Eustrongylides sp., appear to act like predators as it can be seen from their isotope discrimination values. However, future research on additional host-parasite systems and especially on acanthocephalans is needed in order to corroborate these conclusions.

Host identification in unfed ticks from stable isotope compositions (δ13C and δ15N)

“…Overall, the observed lack of impact by confounders is pivotal for the application of isotope compositions because the local populations of questing ticks at a given moment in time contain mixtures of individuals from different cohorts, with varying success with respect to host finding as a result of stochastic processes (Gray, 1991;Randolph et al, 2002). The predictable spacings do not appear to have any of the unusual or unexpected spacings reported for other generalist parasites (Nachev et al, 2017).…”

Polycyclic aromatic hydrocarbons in the cestode Oncomegas wageneri parasite of Mexican flounder Cyclopsetta chittendeni

“…All this bring us to suggest that O. wageneri would be eliminating PAHm but not as efficiently as their host, finally acting as a sinkhole of PAHm. Similar arguments Red areas on maps represent a high mean PAHm concentration for the organisms sampled at each station, whereas blue zones represent a low mean PAHm concentration for parasites acting as sinkholes of heavy metals have been provided by Nachev et al (2017) and Sures et al (2017).…”

“…The first explanation for the higher concentration of PAHm in parasites with respect to their host is that O. wageneri individuals absorb PAHm from the host but do not excrete them efficiently. Owing to the lack of a digestive system, the substances enter the cestodes across the tegument; therefore, the cestodes ingest and absorb the same type of food acquired by the host (Nachev et al 2017;Sures et al 2017), a characteristic that places O. wageneri in the same trophic level of the host. For such host-parasite systems, no significant difference between pollutant concentrations in the hosts and the parasites would be expected (see Le et al 2014).…”

Mixing models and stable isotopes as tools for research on feeding aquatic organisms

“…In recent decades, there has been increased research using techniques involving stable isotopes (DENIRO & EPSTEIN, 1977;1978;1981;FANTLE et al, 1999;FRY, 2006;BEZERRA et al, 2015;VIGHI et al, 2016;NACHEV et al, 2017). This analysis is widely used to investigate various Moraes & Henry-Silva. scientific issues pertaining to organisms and their ecosystems, especially concerning eating habits and availability of nutritional sources in life stages, whether in their natural environment or in captivity (PASQUAUD et al, 2010;GONDWE et al, 2011;KADYE & BOOTH, 2012;LETOURNEUR et al, 2013;RAO et al, 2015).…”