The blood-sucking tick Ixodes hexagonus reveals dietary stable isotope signatures of mammalian hosts

Abstract

Ticks are obligate haematophagous ('blood-sucking') ectoparasites that are capable of retaining host dietary traces post-moult, providing an opportunity to investigate parasite-host interactions and explore their potential as non-invasive subsampling techniques. However, research on the preservation of biochemical host signatures within whole engorged parasites remains limited. Here, we examine stable isotope ratios of nitrogen (δ15N) and carbon (δ13C) across different tick tissues (exoskeleton vs. blood meal) and between whole ticks and one of their hosts, the European polecat Mustela putorius. Additionally, carbon and nitrogen weight percentages (wt%) are assessed to explore potential biochemical changes linked to blood meal digestion. Our findings showed that the isotopic composition of tick exoskeleton and blood meal differed significantly, with exoskeletons potentially reflecting a previous host. Whole engorged ticks showed a close δ15N relationship to their host, consistent with that of trophic enrichment, while the observed δ13C values were more variable. These findings enhance our understanding of how haematophagous parasites preserve host dietary signatures and, with further research, could support their use as a valuable alternative to invasive sampling methods, particularly when destructive sampling is not feasible.

Fig 1. Typical life cycle of a three-host ixodid tick.

Larvae hatch from eggs before finding a host and taking a blood meal, after which they drop off the host to moult into nymphs. Nymphs repeat this process, moulting into adults after feeding. On the host, males seek out females to mate with while taking small meals themselves and repeating this process several times before dying. Mated females will engorge themselves on blood to fuel their final act; dropping off their host and laying thousands of eggs [21].

Fig 2. Nitrogen and carbon isotope ratios (‰) in tick blood meals and exoskeletons.

Mean (i) δ¹³C (in white) and δ¹⁵N (in grey) in ‰, (ii) stable isotope ratios of nitrogen (δ¹⁵N) and carbon (δ¹³C), (iii) mean carbon to nitrogen ratio (C:N) values of tick blood meals (n = 6) and exoskeletons (n = 6). (iv) carbon wt% and nitrogen wt% of blood meals with regression lines, where each pair of data points represents an individual tick. Tukey grouping shows statistical significance, dotted lines signify samples belonging to the same tick, and outliers are indicated by *.

Fig 3. Regression lines of nitrogen and carbon isotope ratios (‰) between ticks and polecat host tissues.

Relationships between δ¹⁵N (i-ii) and δ¹³C (iii-iv) in ‰ of (i, iii) polecat whisker and whole tick, and (ii, iv) polecat muscle and whole tick, including regression lines.

Fig 4. Nitrogen and carbon isotope ratios (‰) of ticks and their host, the European polecat (whiskers and muscle), as well as rabbit muscle, and polecat diet.

Mean δ¹⁵N and δ¹³C (±SD in ‰) of whole ticks (each data point represents the mean of 3 ticks per host; n = 30), and polecat whiskers (n = 10) and muscle (n = 6). Polecat whole blood (i) and diet (ii) were calculated using muscle and data from red foxes V. vulpes [59]. Isotopic data (iii) from Neilson et al. [63] on British rabbit muscle (n = 6) were included as potential polecat prey. Analytical uncertainty is shown in bottom left.