Stable isotope analysis of ectoparasites as a tool for understanding trophic interactions with mammalian hosts

Climate change is expected to expand the geographic ranges of
ectoparasites, increasing the transmission of vector-borne diseases and
thereby necessitating a better understanding of ectoparasite-host trophic
dynamics. Haematophagous ectoparasites can serve as valuable subsamples of
their hosts, retaining isotopic values that reflect dietary information in
both their blood meals and tissues. However, the differences in the
lifestyles and feeding strategies of lice, fleas, and ticks may influence
how these isotopic values are preserved. Here, stable isotope values of
carbon (δ13C) and nitrogen (δ15N) were used to investigate trophic
interactions between ectoparasites and their mammalian hosts in three
pairings: lice (Anoplura: Polyplacidae; n = 101) and Eurasian red
squirrels Sciurus vulgaris, fleas (Siphonaptera: Ceratophyllidae; n = 92)
and fat dormice Glis glis, and ticks (Ixodida: Ixodidae; n = 16) and
European hedgehogs Erinaceus europaeus. Our findings indicate
ectoparasites reflect the dietary patterns of their host, with lice
exhibiting the closest isotopic values, followed by fleas and ticks. All
ectoparasites had significantly higher nitrogen isotope values compared to
those of their hosts, indicative of trophic enrichment, but their carbon
isotope values varied. Notably, we found that the presence of a blood meal
did not significantly affect the isotopic values found in lice and fleas,
while ticks showed a significant difference between exoskeleton and blood
meal in δ13C values. This study highlights the importance of understanding
how the life histories of parasite species influence the preservation of
isotopic host signals in order to be able to utilise stable isotope
analyses of ectoparasites (particularly lice) to infer host dietary niches
and preferences, with broader implications for understanding host-parasite
dynamics and predicting disease transmission pathways.