Rapid environmental change, including global warming, presents significant challenges in adaptation for all residents of a changing biome. The ability to adapt to these challenges, to cope with the environmental stresses created by them, is a key factor in determining what species are likely to survive and which might be pushed to extinction. Species that have adapted for life in some of the planets most extreme environments are often hit hardest by both the physical and oxidative stress consequences of environmental change. These species are considered indicator species with their struggles providing the first noticeable hints of significant pressure on their ecosystem.
The American Pika, a small relative of rabbits and hares, is an excellent example of a thermally sensitive, cold-adapted specialist species. American Pikas, for the most part, live in higher altitude environments with moist cool climates. They have extremely high metabolisms and thick insulating fur that limits heat loss to the environment. These adaptations allow Pika populations to survive in alpine ecosystems without the need to hibernate during the colder months. However this cold adaptation comes at a price. Pikas typically have a resting body temperature that is only a few degrees below their lethal threshold, so it is very easy for quite moderate rises in temperature to kill Pika. They will instinctively seek cooler microclimates to regulate their body temperature on warmer days, but as the planet warms, these cool hiding places are harder and harder to find within the Pikas’ traditional ranges. Studies have shown the minimum elevation at which Pikas can be found has risen by roughly 150 meters in the last 100 years, while average temperatures worldwide have risen by approximately 0.75 °C over the same time period. A major physiological response to long-term environmental pressure is the activation of the HPA axis resulting in the release of glucocorticoids into the bloodstream. Glucocorticoids such as cortisol and corticosterone mediate a variety of adaptive responses to stressful stimuli including behavioral changes and increasing energy via upregulation of glucogenesis. While these responses can be beneficial to short term survival, chronic long term activation of the HPA axis has detrimental consequences, including suppressed immune response, reduced growth, protein loss and decreased cognitive functioning. For individuals already attempting to physically adapt to a changing environment, these additional challenges can easily become insurmountable.
For researchers studying Pika in the hopes of preserving the species in the wild, it is critical not just to understand changes in population, range and population density, but also to understand the stress individuals are experiencing because of these changes. Researchers therefore often seek to measure corticosterone in individual animals (Arbor Assays DetectX Corticosterone EIA and CLIA Kits). The type of samples in which corticosterone is measured can significantly influence results, since the rate at which corticosterone is deposited in different sample types will vary. Measuring corticosterone in serum or plasma provides a very immediate assessment of stress. Corticosterone is released into the blood relatively quickly after a stressful event, and may rise and fall over the period of just a few hours. These samples can provide a very immediate snapshot of stress in an individual, but the timing of sample collection is critical if one hopes to be able to correlate multiple animals or populations. Fecal samples provide information on corticosterone levels over the time period that material has been passing through the digestive tract. Depending on species this could be a few days to a week or more. Fecal samples have the plus of being non-invasive, but it can be difficult to assign samples to individuals in the wild. Collecting a range of samples can however provide reasonably good information on how much stress a population as a whole is under at the moment. Hair samples are emerging as means of looking at glucocorticoid stress over longer time frames. The corticosterone (or cortisol) accumulates over the entire growth period of the hair. So a hair samples from a number of individuals can provide information on general stress of months or a season. This is especially relevant if they can be compared to populations of Pika that are under little to no pressure to provide baseline levels.
Careful study of indicator species such as the Pika can provide us with a great deal of information on how environments overall are impacted by environmental stressors like climate change or habitat disruption. These data are critical for protecting and preserving our native species and their habitat ranges for future generations.