A novel technique to measure chronic levels of corticosterone in turtles living around a major roadway.

J. H. Baxter-Gilbert,J. L. Riley,D. Lesbarreres,J. D. Litzgus,G. F. Mastromonaco

doi:10.1093/conphys/cou036

Abstract

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.

Highlights

In the face of dramatic biodiversity loss (Butchart et al, 2010; Hoffmann et al, 2010), conservation-based research is being applied to a broad range of disciplines (e.g. reproductive biology, Wildt and Wemmer, 1999; population genetics, Holderegger and Di Giulio, 2010; thermal ecology, Monasterio et al, 2013) and typically includes topics that extend beyond those addressing the most obvious threats to species
In addition to the comparison of CORT levels made between the two study sites used to test our hypothesis, we examined the relationship between body condition and baseline stress levels, which is relatively under-studied in freshwater turtles
By understanding the physiological effects caused by human disturbance, conservation actions can be directed towards understanding the indirect threats, which have until recently remained unstudied (Ellis et al, 2012)

Summary

Introduction

In the face of dramatic biodiversity loss (Butchart et al, 2010; Hoffmann et al, 2010), conservation-based research is being applied to a broad range of disciplines (e.g. reproductive biology, Wildt and Wemmer, 1999; population genetics, Holderegger and Di Giulio, 2010; thermal ecology, Monasterio et al, 2013) and typically includes topics that extend beyond those addressing the most obvious threats to species (e.g. habitat destruction, over-harvesting, emerging diseases, invasive species; Wilcove et al, 1998). Road ecology typically focuses on the impacts of the direct threats of road mortality and habitat and population fragmentation on populations (Shepard et al, 2008; Clark et al, 2010). These threats are both prevalent and relevant, they are unlikely to be the only negative effects posed by roads to local wildlife populations. If we are to develop a complete understanding of threats to populations posed by roads, we must look beyond the direct impacts of roads themselves One such avenue of investigation resides in endocrinology, in promoting the understanding of anthropogenically associated physiological stress (Newcomb Homan et al, 2003; Partecke et al, 2006; Van Meter et al, 2009). Roads present a host of potential stressors in the forms of vehicle encounters, as well as sound, light and chemical pollution (Longcore and Rich, 2004), yet the impacts these potential stressors have on the physiological state of reptiles remain unknown

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