Ticks on Lizards: Parasite-Host Interactions of the Southern Alligator Lizard (Elgaria multicarinata) in Washington State

I investigated interactions between ectoparasites (ticks) and their host, the southern alligator lizard (Elgaria multicarinata). Alligator lizards are capable of complement-mediated killing of the Lyme disease spirochete carried by ticks and may potentially reduce Lyme disease prevalence by cleansing pathogenic organisms from ticks. Despite this, little is known about host-parasite dynamics in alligator lizards. My goals were to 1) assess patterns of tick presence (i.e. parasite load) on alligator lizards and 2) investigate potential negative effects of ticks on alligator lizards. I sampled lizards during the summer of 2019 near Catherine Creek, along the Columbia River Gorge in southern Washington. Ticks were counted on all lizards captured, removed with tweezers, and stored for later analysis. Lizards were weighed, measured (snout-tovent length, tail length), and released on the study site. A “body condition index” was determined for each lizard and compared to its parasite load to test the hypothesis that ticks are associated with reduced lizard fitness (Jakob et al. 1996). Parasite load averaged 0.4 ticks/lizard (range: 0- 2), with 25% of 16 lizards sampled having at least 1 tick. Ticks showed a preference for lizards with longer tails, a result which matches observations of other studies of E. multicarinata. I found no relationship between tick presence and lizard body condition. Our research is ongoing, using molecular techniques such as diagnostic PCR to determine the tick species involved (possibly Ixodes pacificus, the western black-legged tick) and whether E. multicarinata could reduce the amount of Lyme disease and Rocky Mountain spotted fever in Washington’s ticks