Non-invasive Methods for Measuring and Monitoring Stress Physiology in Imperiled Amphibians

Abstract

Global climate change is negatively impacting global biodiversity and ectothermic vertebrates, with amphibians being the most imperiled vertebrate taxa. Increased mean global atmospheric temperatures, high rates of habitat degradation, and exposure to infectious diseases, such as chytridiomycosis, have contributed to population declines and extinctions of rare and endangered amphibian species. Field-based monitoring of physiological endocrine traits can help determine the sub-lethal effects of environmental stressors and provide early alerts when populations are chronically stressed. Recent advances in amphibian stress endocrinology include the development and use of non-invasive methods to quantify the glucocorticoid, or stress biomarker, corticosterone. Non-invasive methods, such as urinary, skin and buccal swabs, and water-borne hormone monitoring methods (suited for terrestrial and aquatic dwelling species), are available to quantify baseline and short-term physiological stress responses of amphibians under field settings. In this review, we illustrate, by using two case studies of aquatic and terrestrial amphibian species, the applications of non-invasive corticosterone monitoring methods to advance the ecological knowledge and conservation of imperiled amphibian species, discuss the limitations of these methods, and provide future directions for the use of non-invasive hormone monitoring methods. We highlight the use of non-invasive field endocrinology methods to monitor the impacts of environmental stressors on the physiology of amphibians, which can be applied to advance ecological research, conservation, and management of imperiled species.

Evaluating corticosterone as a biomarker for amphibians exposed to increased salinity and ambient corticosterone

“…The two measures of CORT may therefore also have different biological meanings and require different interpretations and may not be appropriate to validate against one another ( Millikin et al , 2019 ). Despite weak or no correlation between interrenal and waterborne CORT in this study, previous studies have illustrated that waterborne CORT is biologically meaningful for many species and correlated with plasma or whole-body CORT levels (reviewed in Baugh et al , 2018 ; Narayan et al , 2019 ). Second, equilibrium effects occurring from high ambient CORT could have confounded relationships between interrenal and waterborne CORT.…”

“…Waterborne CORT has been physiologically and biologically validated for many fish and amphibian species ( Scott and Ellis, 2007 , Narayan, 2013 , Narayan et al , 2019 ). For physiological validation, studies often compare waterborne to plasma or whole-body CORT to ensure concentrations in water correlate with endogenous concentrations of CORT ( Scott and Ellis, 2007 , Gabor et al , 2013a , Millikin et al , 2019 ).…”

“…Waterborne CORT is a novel, non-invasive collection method for aquatic vertebrates that provides an integrated measure reflecting CORT levels over a 1–2-h collection period ( Scott and Ellis, 2007 ; Narayan et al , 2019 ). Integrated measures are suggested to be more reliable indicators of stress than instantaneous measures (e.g.…”

“…To our knowledge, the pervasiveness, variability and effects of ambient CORT are not well understood (but see Stavreva et al , 2012 ; Gabor et al , 2018 ). Nevertheless, waterborne CORT has been used to evaluate physiological effects of contaminants, disease and invasive predators on aquatic vertebrates such as amphibians ( Gabor et al , 2015 , 2018 ; Narayan et al , 2019 ).…”

Age, size and body condition do not equally reflect population response to habitat change in the common spadefoot toadPelobates fuscus

“…In this context, it is important to identify the most suitable monitoring tools that will detect early changes in population health before severe declines occur. Amphibian populations, due to their sensitivity to environmental stress, are often used in biomonitoring, and as such a variety of both invasive and non-invasive tools are available for estimating and measuring the impact of human activities, like fluctuating asymmetry (e.g., Niemeier, Mueller & Roedel, 2019), micronuclei tests (e.g., Bosch, Gorla & Aiassa, 2011), immunocompetence (e.g., Brown, Shilton & Shine, 2011), stress physiology (Narayan et al, 2019) or measures of heterozygosity (Eterovick et al, 2016). Our study showed that body measurements that require minimal handling of the animal and can be done on site provide a reliable measure of the effects of habitat loss and fragmentation.…”