Host preferences of bat flies: following the bloody path of stable isotopes in a host–parasite food chain

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Abstract
Almost all mammals are infested with ectoparasites, but even though parasites may have a strong impact on their host, their host specificity is often unknown. We studied the host preferences of two bat fly species, Strebla wiedemanni Kolenati, 1856 and Trichobius parasiticus Gervais, 1844, identified on the common vampire bat, Desmodus rotundus (E. Geoffroy, 1810), using stable carbon isotopes. Since D. rotundus was part of the C4 food web and other bats sharing the roost with D. rotundus were part of the C3 food web, bat flies were exposed to two isotopically distinct potential hosts. The δ13C values of the two bat fly species collected from D. rotundus were similar (–11.5‰ ± 1.1‰ (mean ± SD) for S. wiedemanni and –12.4‰ ± 1.9‰ for T. parasiticus) and identified them as members of the C4 food web, although their δ13C value was significantly lower by –1.7‰ ± 2.6‰ than that of the corresponding host individual. The δ13C value of bat flies collected from Carollia perspicillata (L., 1758) sharing roosts with D. rotundus averaged –24.2‰ ± 0.3‰, which was also significantly lower by –1.3‰ ± 1.1‰ than the host's δ13C value. We concluded that the negative shift in δ13C of D. rotundus bat flies relative to the host individual was caused by isotopic fractionation rather than by a mixed diet. The enrichment in nitrogen-15 from S. wiedemanni and T. parasiticus to D. rotundus equaled 2.3‰, which indicates one trophic step between the host and the parasite. In summary, both bat fly species preferred D. rotundus over other bat species and are therefore truly monoxenous parasites.