Assessment of environmental and host dependent factors correlated with tick abundance on Komodo dragons

In this study we assessed interactions among Komodo dragon Varanus komodoensis populations, individual Komodo dragons and two tick parasites Amblyomma robinsoni and Aponomma komodoense to assess variation in host-parasite aggregations. Prevalence of ticks was uniformly high (> 98%) but median tick abundance varied 3.52 fold among 9 host lizard populations. There was no evidence to suggest that average tick abundances were correlated with genetic similarities (Rm = 0.133, P = 0.446) or geographic proximities (Rm = 0.175 P = 0.303) among host populations. Temporal concordance in tick abundance was measured for host populations between two different years but not for the individual hosts within these populations. General linearized modelling indicated that ≈ 23% of host variation in tick abundance was positively correlated to a multivariate function incorporating lizard body size, body condition, their interactions, and habitat differences. The covariates of host population density and inbreeding coefficients, which are often associated with significant variation in parasite abundance, were not associated with variation in tick abundance on Komodo dragons. However, despite larger lizards generally harbouring more ticks, relative levels of ticks (controlling for host body mass differences) indicated that smaller individuals carried significantly higher tick abundances compared to larger lizards. There was no significant interaction between tick abundance and an individual host’s growth rate. The major implications of our results indicated considerable variation in tick abundance across their host’s range and that host body size is likely to be a significant determinant to what degree ticks impact the fitness of their hosts.