Anti-parasitic function of tree-rubbing behaviour in brown bears suggested by an in vitro test on a generalist ectoparasite

Abstract

Rubbing against various objects or self-anointing with pungent substances are behaviours observed in many mammal species. The brown bear (Ursus arctos) is a non-territorial species that rubs against trees with the main purpose being intraspecific communication. In addition, some odorous substances are known for eliciting rubbing behaviour and hence are used to lure bears to trees in studies relying on non-invasive hair collection. Tree-rubbing is often accompanied by clawing and debarking which release tree resin that impregnates the fur and can potentially deter ectoparasites. Here, we present a study aiming to determine whether ticks, being widely spread and an important vector of pathogens, are repelled by resin products known to attract bears and elicit rubbing behaviour, namely turpentine and beech tar. Dermacentor reticulatus ticks were offered a binary microhabitat choice by placing them in the middle of individual horizontal tubes with tested substances placed on filter paper at one end, and distilled water as a control (neutral) substance at the other. Their behaviour was recorded for three minutes. Ticks consistently touched the neutral end of the tube while avoiding treated ones. Overall, ticks remained at greater distances from treatments than from water. A fitted logarithmic regression showed ticks did not spend more than seconds at a treated side, supporting our prediction that ticks are repelled by turpentine and beech tar. Parasite repellency may bring a further advantage in rubbing behaviour trade-offs, compensating some energetical costs, and adds a trait to the behaviour important in seemingly divergent contexts of intraspecific communication and defense against ectoparasites.