Malarial Parasitism and the Behavior of the Lizard, Sceloporus occidentalis

Abstract

The behavioral time budget of the western fence lizard, Sceloporus occidentalis, was recorded in northern California, where fence lizards are frequently infected by the malarial parasite, Plasmodium mexicanum. Because malarial infection results in pathologies that could affect the host's behavior in nature, time budgets of malarious and noninfected animals were compared. Malarious and noninfected lizards utilized the microhabitat in similar ways, except that infected animals perched more often in shade. Fully 94% of the time lizards were observed, they spent perched, unmoving and apparently visually scanning the local area. Although behavior patterns differed seasonally and between sexes and age classes, they were very similar in infected and noninfected lizards. Noninfected adult males, though, spent more time engaged in social behaviors than did malarious males. Social interactions appear strenuous, occasionally lasting several minutes. Such social activities by the lizard may depend on rapid oxygen consumption that is disrupted by Plasmodium infection. Number of burst runs and length of runs were similar for both infected and noninfected animals; most lasted less than 1 sec, and the longest covered 6 m. In laboratory experiments, recovery from burst runs was rapid (less than 1 min/sec of running), probably negating any ecological consequences of an effect of the parasite on rate of metabolic recovery by infected lizards. The behavior of malarious lizards, compared to noninfected animals, can be explained by the effects of Plasmodium infection on the host's energy metabolism, as measured in the laboratory. These results demonstrate that estimating the virulence of parasitic infection requires both laboratory studies and observation on the host in a natural setting.