Biochemical Markers for Thermal Stress in North American Pikas (Ochotona princeps)

Abstract

North American pikas (Ochotona princeps) are a high altitude keystone species that are indicative of that ecosystem’s condition. Over the last twenty years, numerous populations of pikas have declined or disappeared. Because pikas are exceptionally sensitive to high ambient temperatures, it has been suggested that these declines are due to thermal stress imposed by climate change. Thermal stress has been shown to cause oxidative stress through an increased cellular concentration of oxygen radicals. Therefore, levels of oxidative stress markers are strong indicators of thermal stress. In order to quantify the degree of thermal stress placed on pika populations, fecal and plasma samples were assayed for a number of biochemical markers over a range of altitudes and ambient temperatures. Fecal corticosterone levels were assayed as a marker for long-term stress. Oxidative stress markers, including thiobarbituric acid reactive substances (TBARS), 8-hydroxy-2-deoxy guanosine (8-OH-dG) and glutathione peroxidase (GPX), were used to assess disparities in oxidative stress among pika populations. Results show low elevation pikas to have higher corticosterone levels in early summer when compared to late summer but no other correlations have been found. More sampling and testing are required to determine if other relationships exist.