Non-invasive reproductive and stress endocrinology in amphibian conservation physiology

Abstract

Non-invasive endocrinology utilizes non-invasive biological samples (such as feces, urine, hair, aquatic media and saliva) for the quantification of hormones in wildlife. Urinary based enzyme-immunoassay (EIA) and radio-immunoassay (RIA) have enabled the rapid quantification of reproductive and stress hormones in amphibians (Anura: Amphibia). These methods can be used to assess the ovarian and testicular endocrine functions, and physiological stress in captive and free-living populations with minimal disturbances. Non-invasive endocrine monitoring has therefore greatly advanced our knowledge of the functioning of the stress endocrine system - the hypothalamo-pituitary interrenal [HPI] axis and the reproductive endocrine system - the hypothalamo-pituitary gonadal [HPG] axis in amphibian physiological stress response, reproductive ecology, health & welfare and survival. Biological (physiological) validation is necessary for obtaining the excretory lag-time of hormone metabolites. Urinary based EIA for the major reproductive hormones, estradiol and progesterone in females and testosterone in males, can be used to track the reproductive hormone profiles in relation to reproductive behavior and environmental data in free-living anurans. Urinary based corticosterone metabolite EIA can be used to assess the sub-lethal impacts of biological stressors (such as invasive species and pathogenic diseases) as well as anthropogenic induced environmental stressors (e.g. extreme temperatures) on free-living populations. Non-invasive endocrine methods can also assist in the diagnosis of success or failure of captive breeding programmes by measuring the longitudinal patterns of changes in reproductive hormones and corticosterone within captive anurans and comparing the endocrine profiles with health records and reproductive behavior. This review paper focuses on the reproductive and the stress endocrinology of anurans and demonstrates the uses of non-invasive endocrinology for advancing amphibian conservation physiology. It also provides key technical considerations for future research that will increase the data accuracy and reliability, and the value of non-invasive endocrinology within the conceptual framework of conservation physiology.