Tick infestations in the Namaqualand speckled padloper, Homopus signatus signatus (Gmelin, 1789)

Abstract

Many terrestrial chelonians are parasitized by ticks, but we have a poor   understanding of what determines tick infestations on chelonian hosts. We counted ticks on Homopus signatus signatus during each spring in the years 2001–2004, and evaluated tick frequencies in relation to tortoise anatomy, climate and  microhabitat. Tortoises hosted Ornithodoros compactus and O. savignyi, and ticks seemed to prefer the hindlimbs, avoid the shell, and use the forelimbs and neck in intermediate frequencies. The number of ticks on the neck and forelimbs did not differ among males, females and juveniles, but for the hindlimbs and all body parts, males and females usually had similar tick numbers and adults often had more ticks than juveniles. The number of ticks on the hindlimbs correlated with the body size of male and female tortoises, whereas the number of ticks on the forelimbs correlated with juvenile body size. Males and females had similar incidences of ticks despite sexual dimorphism in body size (female size > male size), and this may be due to the relatively large shell openings (soft skin exposure) of males compared to females. Body condition and microhabitat had no effect on the number of ticks. It is unclear why tick numbers on H. s. signatus increased in dry years. The adverse effects of drought on mammals may have caused ticks to switch from mammals to tortoises when preferred hosts were no longer available.

Keywords: host switching, morphology, Ornithodoros, parasite, sexual dimorphism, tortoise.