Hot off the Press: Novel Technique to Measure Stress from Turtle Claws
Investigating how stress impacts wild populations, especially in light of huge human-caused changes, is a big question in conservation biology. Does increased urbanization effect stress of animals, and in turn their immune response or reproductive success?
The first step to answering these questions is having a reliable, practical method of measuring long-term stress from wildlife in natural populations. Traditional techniques can involve drawing blood, and requiring this blood to be stored properly in a freezer in the field - a task that can be both invasive to the individual and logistically challenging for many researchers. Also, most methods of measuring stress sample short-term stress by measuring corticosterone (a stress hormone) in blood (capturing days), or hair and faeces (capturing weeks).
For his MSc, James Baxter-Gilbert and his collaborators developed a novel technique of measuring corticosterone from turtle claws! This method is logistically feasible for samplign in the field, as well it capture long-term stress levels (over months or years) in a wild population. Hopefully this method will provide new avenues for research about how stress affects wildlife populations.
Conservation biology integrates multiple disciplines to expand the ability to identify threats to populations and develop mitigation for these threats. Road ecology is a branch of conservation biology that examines interactions between wildlife and roadways. Although the direct threats of road mortality and habitat fragmentation posed by roads have received much attention, a clear understanding of the indirect physiological effects of roads on wildlife is lacking. Chronic physiological stress can lower immune function, affect reproductive rates and reduce life expectancy; thus, it has the potential to induce long-lasting effects on populations. Reptiles are globally in decline, and roads are known to have negative effects on reptile populations; however, it is unknown whether individual responses to roads and traffic result in chronic stress that creates an additional threat to population viability. We successfully extracted reliable measures of corticosterone (CORT), a known, commonly used biomarker for physiological stress, from claw trimmings from painted turtles (Chrysemys picta) captured at three study sites (road-impacted site, control site and validation site). Corticosterone levels in claws were evaluated as a measure of chronic stress in turtles because CORT is deposited during growth of the claw and could provide an opportunity to examine past long-term stress levels. While male turtles had higher CORT levels on average than females, there was no difference in the level of CORT between the road-impacted and control site, nor was there a relationship between CORT and turtle body condition. In validating a novel approach for non-invasive measurement of long-term CORT levels in a keratinized tissue in wild reptiles, our study provides a new avenue for research in the field of stress physiology.
Baxter-Gilbert, J. H., Riley, J. L., Mastromonaco, G. F., Litzgus, J. D., and Lesbarreres. 2014. A novel technique to measure chronic levels of corticosterone in turtles living around a major roadway. Conservation Physiology 2: 1-9.
Download PDF here