Thermal preferences of infected lizards and abundance of vectors might explain a high blood parasite prevalence

Ectotherm physiology operates optimally within a thermal range. However, when ectotherms are infected, they can respond with subtle, yet significant, adjustments in their thermal behavior. This behavioral plasticity acts at the expense of reducing the pathogen’s fitness. A previous study on males of a Mediterranean lizard, Psammodromus algirus, found that lizards responded with behavioral hypothermia to the inoculation of a bacterial antigen. We experimentally assessed whether males of the same lizard species can have a similar reaction norm against natural infections. To this end, half of a 37-adult male sample was assigned to a deparasitization treatment that significantly reduced the number of hematophagous mites compared to a control group and quantified the parasitemia of Karyolysus and Schellackia, two genera of blood parasites transmitted by hematophagous mites. To test for a reaction norm in response to these parasites, we compared the thermal behavior of the lizards before and after the deparasitization. We found a significant interaction between the parasitemia of Karyolysus and the deparasitization treatment that suggested lizards in the deparasitized group selected higher temperatures in response to greater blood parasite load (behavioral fever), whereas in the control group, individuals with high blood parasite loads tended to select lower temperatures (behavioral hypothermia). The relatively cooler thermal preference of lizards with both high mite loads and high Karyolysus parasitemia combined with the fact that lizards are subject of heat stress during seasonal peaks of mite abundance can explain the high prevalence of Karyolysus in the studied population.