HORMONAL ALTERATIONS AND REPRODUCTIVE INHIBITION IN MALE FENCE LIZARDS (SCELOPORUS-OCCIDENTALIS) INFECTED WITH THE MALARIAL PARASITE PLASMODIUM-MEXICANUM

When naturally infected with the malarial parasite Plasmodium mexicanu m, Western fence lizards Sceloporus occidentalis, exhibit numerous rep roductive pathologies. Infected males display fewer courtship and terr itorial behaviors, have altered sexually dimorphic coloration, and hav e smaller testes. Infected animals store less fat by late summer, whic h, for females, reduces clutch size in the spring. We describe hormona l alterations associated with malarial parasitism that may underlie th is reproductive inhibition. We caught lizards in the field and bled th em either immediately or 1 h after capture for measurement of basal an d stress levels of steroid hormones Compared to uninfected lizards, in fected lizards had bower levels of basal plasma testosterone (24 vs. 3 8 ng/mL) and higher bevels of corticosterone (18 vs. 8 ng/mL) followin g 1 h of capture and confinement. Infected animals also had lower leve ls of plasma glucose (243 vs. 270 mg/dL). When we experimentally eleva ted plasma corticosterone of uninfected lizards in large outdoor enclo sures, the animals showed decreases in testosterone, testis size, and stored fat similar to those of infected animals in the wild. We hypoth esize that the parasite induces alterations in the adrenal response to acute stress, resulting in a suppression of testosterone and the inhi bition of reproductive behavior.