The Effect of Exogenous Testosterone on Ectoparasite Loads in Free‐Ranging Western Fence Lizards

Abstract

Numerous factors impact the dynamics of host-parasite relationships, such as host sex, hormonal state, reproductive condition, host health, and behavior. In particular, males from a variety of taxa frequently carry heavier parasite burdens than females, particularly during breeding season when testosterone concentrations are elevated. Using western fence lizards (Sceloporus occidentalis), we tested the hypothesis that high circulating testosterone concentrations in male lizards induce high tick and mite loads. We implanted male lizards with either testosterone or control implants in the field during the spring, when tick and mite loads are highest. One month later, testosterone-implanted males had significantly higher tick loads, but lower mite loads, than control males. These results suggest that testosterone differentially impacts ectoparasitic acarine burdens. Testosterone may modulate aspects of lizard physiology and behavior that enhance or diminish parasitism by certain acarines during periods of peak reproductive effort.

Territorial Behavior and Cortical Brain Plasticity in Adult Male Sceloporus Occidentalis

“…These are supported by data from other populations of S. occidentalis, where aggressive responses are significantly increased during the spring season and drop drastically by early June (Klukowski & Nelson, 1998). Additionally, in previous studies on this population of S. occidentalis there was no difference in behavior between T treated and castrated lizards, indicating T concentrations alone may not cause behavioral changes in this population (Pollock et al, 2012). It may be that seasonal changes in behavior are not present in this S. occidentalis population but despite this possibility, it seems more likely that the collected data was insufficient to detect a seasonal difference.…”

“…Interestingly, neurogenesis in the MC and DC of the Tenerife lizard (Gallotia galloti) is at its highest during its mating season, the spring (Delgado-Gonzalez et al, 2008). Spring is also the mating season for S. occidentalis and a time of the year that is marked by elevated T levels and territorial behavior in males (Fitch, 1940;Pollock et al, 2012). Furthermore, lizards with larger territories have higher T levels than those with smaller territories (Sinervo et al, 2000).…”

Effects of testosterone on the spatial ecology, coloration, and brain regions in western fence lizards, Sceloporus occidentalis

“…Our T implanted individuals averaged plasma T levels of 75.89+22.17 ng/mL while our control individuals had plasma T levels of 8.28+4.18 ng/mL. Another study on S. occidentalis reported T levels as 21.1+2.8 ng/mL (Pollock et al, 2012). Other studies on Sceloporus report breeding T levels of 7.7+2.8 ng/mL in S. undulatus (Klukowski et al, 2001) and 46.4+5.9 ng/mL in S. yarrowii (Cox et al, 2008).…”

“…The aim of this study was to determine the effect of ecologically relevant doses of T on home range size and coloration, however our treatment resulted in pharmacological doses of T. Our implants were constructed following the methods of a previous researcher who obtained ecologically relevant doses (Pollock et al, 2012).…”

“…Other studies on Sceloporus report breeding T levels of 7.7+2.8 ng/mL in S. undulatus (Klukowski et al, 2001) and 46.4+5.9 ng/mL in S. yarrowii (Cox et al, 2008). Our implants were constructed following the methods of a previous researcher who obtained physiologically relevant doses (Pollock et al, 2012).…”