Consistent individual differences in ecto-parasitism of a long-lived lizard host

Individual hosts vary substantially in their parasite loads. However, whether individual hosts have consistently different loads remains uncertain. If so, hosts that have consistently high parasite loads may serve as key reservoirs or super-spreaders. Thus, identifying whether individuals persistently differ in their parasitism and the factors that explain these patterns constitute important issues for disease ecology and management. To investigate these topics, we examined nine years of tick counts in a wild population of sleepy lizards, Tiliqua rugosa. Lizards were individually marked, and throughout their activity season, often across several years, we repeatedly assessed lizards' ticks (to stage – larva, nymph, adult male, and adult female – and species, either Bothriocroton hydrosauri or Amblyomma limbatum). Using these repeated individual measures, we determined whether tick counts were repeatable. Then, we tested predictors of average tick counts, particularly lizard mass, sex, behavioural type (aggression and boldness), and the distance between lizards' home range centre and a road transecting the study site (an area of greater food and lizard activity). We found that lizards exhibited consistent individual differences in tick loads both within and across years. Within-lizard yearly average counts of larvae and nymphs were positively correlated. Lizards closer to the road tended to have more larvae and nymphs of both species and more adult B. hydrosauri. Sex did not affect tick counts. Mass differentially affected adult female A. limbatum and adult male B. hydrosauri tick counts. Intriguingly, lizards with above average aggression but below average boldness, or vice versa, tended to have higher average adult female B. hydrosauri tick counts. Ultimately, our results demonstrate that lizards differed consistently in their tick counts, indicating that lizard parasitism may constitute a phenotypic trait of the individual, with implications for both host-parasite dynamics and broader host ecology.