Blood parasite infection is associated with lower thermoregulatory precision in the lizard Podarcis lusitanicus.

Parasites have the potential to disrupt and induce changes in thermoregulation and behaviour in ectotherm hosts, possibly with deleterious effects. In a previous study, the lizard Podarcis lusitanicus (Lacertidae), when infected with blood parasites of the genus Karyolysus (suborder Adeleorina), were bolder, remained exposed for longer, and tended to explore more. To determine if this behaviour was linked to the lizards' thermoregulatory behaviour, we recorded the temperatures of male lizards with varying blood parasite infection levels in a thermal gradient during their active diurnal period. Infected lizards had lower thermoregulatory precision, indicating an association with the previously observed higher exploratory behaviour of infected individuals. However, parasite infection was not significantly associated with higher median or maximum recorded body temperatures, suggesting that the lizards were not compensating through behavioural fever. While we observed no significant effect on leucocyte counts from the parasite infection or thermal variables, the latter had a different magnitude of effect on the host cellular immune response depending on whether the lizard was parasitised or not. The cellular immune response of parasitised lizards increased less with increasing thermal variables (preferred body temperature, maximum recorded temperature, and thermoregulatory precision), suggesting the parasite infection might be negatively affecting the development of stronger immune responses in these hosts. It is also possible that changes to host thermoregulation and behaviour might benefit the parasite beyond its infectious stage in the intermediate vertebrate host, because increasing exploratory behaviour in the lizard could increase the probability of contact with haematophagous mites, the definitive hosts of Karyolysus sp. Finally, while tail condition was not significantly related to thermal preference, lizards with regenerated tails had significantly higher thermoregulation precision than lizards with original tails, highlighting the need for additional studies on the real impact of tail autotomy and regeneration in thermoregulatory capabilities of lizards.