Abstract
The interactions between host individual, host population, and environmental factors modulate parasite abundance in a given host population. Since adult exophilic ticks are highly aggregated in red deer (Cervus elaphus) and this ungulate exhibits significant sexual size dimorphism, life history traits and segregation, we hypothesized that tick parasitism on males and hinds would be differentially influenced by each of these factors. To test the hypothesis, ticks from 306 red deer—182 males and 124 females—were collected during 7 years in a red deer population in south-central Spain. By using generalized linear models, with a negative binomial error distribution and a logarithmic link function, we modeled tick abundance on deer with 20 potential predictors. Three models were developed: one for red deer males, another for hinds, and one combining data for males and females and including “sex” as factor. Our rationale was that if tick burdens on males and hinds relate to the explanatory factors in a differential way, it is not possible to precisely and accurately predict the tick burden on one sex using the model fitted on the other sex, or with the model that combines data from both sexes. Our results showed that deer males were the primary target for ticks, the weight of each factor differed between sexes, and each sex specific model was not able to accurately predict burdens on the animals of the other sex. That is, results support for sex-biased differences. The higher weight of host individual and population factors in the model for males show that intrinsic deer factors more strongly explain tick burden than environmental host-seeking tick abundance. In contrast, environmental variables predominated in the models explaining tick burdens in hinds.
Highlights
Tick distribution in their hosts is frequently found to be highly aggregated in a few individuals within the host population, which determines that a few hosts are responsible for feeding large amounts of ticks (Shaw and Dobson, 1995; Shaw et al, 1998)
The probability of tick-borne pathogen transmission at the tick-host interface largely depends on the burden of ticks feeding in a single infected individual, especially when cofeeding transmission is of great relevance for the epidemiology of the pathogen (Perkins et al, 2003)
Because we were interested if tick-burdens were affected differentially in male and female deer, we developed three models: a model for red deer males, a model for hinds, and, a model combining data for males and hinds and including “sex” as factor
Summary
Tick distribution in their hosts is frequently found to be highly aggregated in a few individuals within the host population, which determines that a few hosts are responsible for feeding large amounts of ticks (Shaw and Dobson, 1995; Shaw et al, 1998). This ecological feature of tick-host interactions greatly conditions the transmission of pathogens between ticks and their hosts (Perkins et al, 2003).
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