Glucocorticoids as Indicators of Ecosystem HealthEPA Grant Number: F5F21869
Title: Glucocorticoids as Indicators of Ecosystem Health
Investigators: Cyr, Nicole E.
Institution: Tufts University
EPA Project Officer: Just, Theodore J.
Project Period: September 1, 2005 through August 1, 2007
Project Amount: $88,666
RFA: STAR Graduate Fellowships (2005) RFA Text | Recipients Lists
Research Category: Academic Fellowships
Chronic changes in stress hormones such as glucocorticoids (GCs) are known to negatively affect health. Conservation biologists have recently become interested in using GC concentrations as an indicator of the health of animals in a particular population; however, a major problem is that researchers do not know how GC concentrations change in response to chronic stress. Another problem with using GCs as a bioindicator is how to measure GC concentrations. GC concentrations are commonly measured in plasma; though, fecal glucocorticoid (FG) analysis has recently become attractive because FG analysis allows researchers to measure GC concentrations noninvasively. This is specifically appealing to researchers interested in assessing the health of endangered species. There are, however, several unresolved issues with this technique. For example, fecal GC levels my not accurately reflect plasma GC levels due to biological, treatment, and storage issues. I propose a study which combines field and laboratory analysis of GC changes in blood and feces caused by chronic stress. The overall objective of this proposal is to test whether GCs, in either blood or feces, can be used as a biomarker of ecosystem health.
I will employ a recently developed chronic stress model using European starlings (Sturnus vulgaris) under controlled laboratory conditions to make a chronically stressed individual. This model consists of a rotation of 5 acute stressors administered randomly for 30 min 4 times/day at approximately 2hr intervals for 18days. Blood samples will be taken every other day from each individual for plasma GC analysis. Fecal samples will be collected each morning and evening before, during, and after the chronic stress model. This will provide an estimate of daily and nightly fecal GC levels. I will then adapt this model to experimentally induce chronic stress in free-living animals to determine whether changes in plasma and fecal GCs in wild animals correspond to changes found in the lab. Blood and fecal samples will be taken from adults and nestlings in a nest box population. Half of the nests will be subjected to a modified version of the chronic stress model, while the other half will serve as controls.
Based on previous lab studies, I predict that chronic stress in starlings will cause an initial increase in GC concentrations above pre-stress levels during the first week followed by a marked decrease GC concentrations below pre-stress levels throughout the remainder of the chronic stress model. I predict that fecal GC levels during the chronic stress model will follow a similar pattern to changes in plasma GCs. Similarly, I predict that adults sampled at the end of the chronic stress model in the field will have lower plasma GC levels than unstressed adults. It is unknown whether fecal GC levels of chronically stressed animals in the field will be comparable to plasma. However, I expect that fecal GC levels in my field experiment will be lower in chronically stressed animals because confounding factors such as body condition and storage techniques are controlled. If this is the case, fecal GC analysis may prove to be a powerful technique for identifying chronically stressed animals in nature without having to capture and handle the subject.