Hormonal alterations and reproductive inhibition in male fence lizards (Sceloporus occidentalis) infected with the malarial parasite Plasmodium mexicanum
Publication Type: |
Journal Article |
Year of Publication: |
1995 |
Authors: |
K.D. Dunlap, J.J. Schall |
Publication/Journal: |
Physiological zoology |
Keywords: |
corticosterone, malaria, plasmodium mexicanum, reproductive behavior, reproductive behaviour, reproductive pathology, sceloporus occidentalis, testosterone, western fence lizards |
ISBN: |
0031-935X |
Abstract:
When naturally infected with the malarial parasite Plasmodium mexicanum, Western fence lizards, Sceloporus occidentalis, exhibit numerous reproductive pathologies. Infected males display fewer courtship and territorial behaviors, have altered sexually dimorphic coloration, and have smaller testes. Infected animals store less fat by late summer, which, for females, reduces clutch size in the spring We describe hormonal alterations associated with malarial parasitism that may underlie this reproductive inhibition. We caught lizards in the field and bled them either immediately or 1 h after capture for measurement of basal and stress levels of steroid hormones. Compared to uninfected lizards, infected lizards had lower levels of basal plasma testosterone (24 vs. 38 ng/mL) and higher levels of corticosterone (18 vs. 8 ng/mL) following 1 h of capture and confinement. Infected animals also had lower levels of plasma glucose (243 vs. 270 mg/dL). When we experimentally elevated plasma corticosterone of uninfected lizards in large outdoor enclosures, the animals showed decreases in testosterone, testis size, and stored fat similar to those of infected animals in the wild. We hypothesize that the parasite induces alterations in the adrenal response to acute stress, resulting in a suppression of testosterone and the inhibition of reproductive behavior.