Development and validation of a non-invasive glucocorticoid monitoring protocol in reptiles : a thesis presented in partial fulfilment of the requirements of the degree of Master of Science in Zoology at Massey University

Abstract

Glucocorticoids (cortisol and corticosterone) are the main hormones secreted by animals via activation of the hypothalamo-pituitary-adrenal (HPA) axis in response to a stressor. Measuring glucocorticoids as indicators of a stress response can be a useful tool for assessing wildlife health and how an individual or population may be coping in its environment. Blood sampling is currently the most common method used for measuring glucocorticoids in animals; however, use of ‘non-invasive’ methods for measuring glucocorticoids are becoming increasingly popular due to animal welfare concerns and practicality. Glucocorticoids can be measured from alternatives such as faeces, saliva, skin, hair and feathers. Non-invasive techniques in reptiles, however, have been limited mainly to faecal and shed skin samples, but these methods are not suitable for assessing acute responses that reflect glucocorticoid levels circulating in the blood. Saliva, often used for measuring cortisol in mammals, has not been tested as a method in reptiles for measuring corticosterone. Different saliva collection methods were tested in water dragons (Intellagama lesueurii lesueurii) and leopard tortoises (Stigmochelys pardalis) to determine which method would yield the required volumes for corticosterone assay in each species. Each species was grouped into saliva and blood sampling groups, and corresponding samples were collected from animals following a standard stress protocol. Corticosterone responses to the stress protocol in each sample type were compared. Finally, blood samples were taken following either an initial blood sample or saliva sample to determine if saliva sampling resulted in a smaller corticosterone response. Corticosterone was successfully measured in reptile saliva, and a full corticosterone response was measured in saliva for both water dragons and leopard tortoises. Sampling type did not affect corticosterone responses. The ability to measure corticosterone from saliva in reptiles provides a new management tool for assessing and further understanding reptilian stress responses.