The effect of wildfire on stress and ornament expression in female lizards

Background/Question/Methods

In many species, females may influence male reproductive decisions by expressing condition-dependent ornaments that honestly signal phenotypic quality. For instance, female striped plateau lizards (Sceloporus virgatus) seasonally express orange throat patches that provide information about female body condition, mite load, yolk antioxidants and offspring quality. In addition, ornament expression is reduced via artificial elevations of corticosterone, the primary stress hormone of reptiles. In 2011, we were faced with a natural experiment to further test the relationship between ornament expression and stress. A large fire, Horseshoe 2, burned through the Chiricahua Mountains May—June 2011 and was managed through a number of mechanisms including burnout operations that reduced accumulated ground fuel but kept the oak-juniper forest canopy largely intact. Our long-term study site was included in the burnout operations and >80% of the ground was burned. We compared ornament expression and corticosterone levels of females on this site to that of females on a nearby site that remained unburned; additionally, we used historical data to compare ornament expression on the burned site to that of females in same population pre-fire (in 2009).  

Results/Conclusions

The burned site had a reduction in the number of shelters and perches (e.g., fallen logs) and, compared to the unburned site, had much larger fluctuations in both temperature and humidity, suggesting the post-fire habitat may be stressful for these small ectothermic lizards. However, females on the two sites did not differ in plasma corticosterone levels at the time of sampling, which occurred 4 weeks post-fire. It is possible that females had acclimated physiologically to the burned conditions by this time or that they are resistant to elevations in glucocorticoids during the reproductive season. Regardless, females on the burned site developed significantly smaller and less colorful ornaments relative to females on the unburned site and females of the pre-fire population. The ornament reduction indicates that females in the post-fire habitat shifted energy allocation from reproduction and display to survival and maintenance, and provides further support for the condition-dependent nature of the female ornament.