Ticks with a preference: not all hosts are the same

Date: 6 October 2016

Introduction: UAntwerp researchers investigated whether ticks have an environment-independent specific preference for particular hosts.

Everyone who regularly goes out for a nature walk in Flanders has experienced unwanted close encounters with a tick.
These encounters have become more and more frequent over the last decades and  they can have unpleasant consequences. Ticks can carry multiple infections, among which Lyme disease. As a result, there is an ever larger scientific interest in these small animals.

Ticks need a blood meal during each life stage: larval, nymphal and adult. Observations seem to indicate that some hosts are more often infested than others. This can be quite important: the mobility of the host determines the distribution of the ticks, and thus also of the infectious disease. It is therefore important to understand why ticks prefer some hosts over others.

However, this is exactly where current knowledge is limited. For example, we do not currently know whether host preference is determined by the environment itself (e.g. humidity, vegetation …) or rather by host-specific characteristics. As part of an FWO-project on the ecology of bird ticks, Raoul Van Oosten, and his colleagues of the research group Evolutionary Ecology (Global Change Ecology Excellence Centre) performed an experiment to address this knowledge gap.

Raoul: “In our experiment we used two tick species, Ixodes arboricola and Ixodes ricinus. The first species lives preferably in birds’ nests and is very host-specific. The second species is a generalist: it can be encountered in variable habitats and has a broad host range including many mammals and birds. As hosts we used great tits, blackbirds and great spotted woodpeckers. Great tits are frequently infested with both tick species, blackbirds often by I. ricinus but never by I. arboricola. There are no observations of tick infestation by either one of both species for woodpeckers.”

The researchers investigated whether host-specific characteristics play a role in tick preference. They confronted ticks and hosts with each other in an artificial environment, where external factors could not influence the chance of infestation.

Raoul: “Our experiment showed infestation patterns remarkably similar to those observed in natural environments. This means that host-specific characteristics play a potential key role in tick host preference. It is thus clear that tick infection patterns as currently observed in the field, are not purely determined by encounter-frequency between tick and hosts. There is also a strong inherent compatibility between ticks and certain hosts. We still understand surprisingly little of the complex interactions between hosts and parasites, while this is essential to understand, map and predict the distribution of ticks and the related infections.”

The study was published in Evolutionary Ecology.

Link: http://www.uantwerpen.be/eveco