Abstract
Ecological studies on food webs rarely include parasites, partly due to the complexity and dimensionality of host-parasite interaction networks. Multiple co-occurring parasites can show different feeding strategies and thus lead to complex and cryptic trophic relationships, which are often difficult to disentangle by traditional methods. We analyzed stable isotope ratios of C (13C/12C, δ13C) and N (15N/14N, δ15N) of host and ectoparasite tissues to investigate trophic structure in 4 co-occurring ectoparasites: three lice and one flea species, on two closely related and spatially segregated seabird hosts (Calonectris shearwaters). δ13C isotopic signatures confirmed feathers as the main food resource for the three lice species and blood for the flea species. All ectoparasite species showed a significant enrichment in δ15N relatively to the host tissue consumed (discrimination factors ranged from 2 to 5‰ depending on the species). Isotopic differences were consistent across multiple host-ectoparasite locations, despite of some geographic variability in baseline isotopic levels. Our findings illustrate the influence of both ectoparasite and host trophic ecology in the isotopic structuring of the Calonectris ectoparasite community. This study highlights the potential of stable isotope analyses in disentangling the nature and complexity of trophic relationships in symbiotic systems.
Highlights
Parasites have been by far the missing links in natural food webs partly due to the singularity and multidimensionality of parasitic interactions [1,2]
We found significant differences in isotopic signatures among all four ectoparasite species and host tissues
Trophic structure Sex was not significant for any ectoparasite species analyzed when pooled from different host taxa and breeding colony (H. abnormis (M:24, F:27): d15N F1,51 = 0.126 P = 0.82, d13C F1,51 = 0.235
Summary
Parasites have been by far the missing links in natural food webs partly due to the singularity and multidimensionality of parasitic interactions [1,2]. Trophic studies in host-parasite networks are scarce and traditional approaches applied to characterize parasite feeding preferences and host use have important drawbacks or are of difficult endeavour in natural conditions [4]. These include for example behavioural and observational studies of parasite dietary breadth, laboratory experiments on parasite feeding preferences and direct examination of parasite’s gut contents. Most of these methods are qualitative whereas the temporal integration they provide is usually very short [1,5]. The use of indirect methods, such as biochemical markers, can expand our understanding of parasite trophic ecology and represent an alternative and innovative tool in host-parasite food-web studies [6]
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