Neutrophil:Lymphocyte Ratio as a Possible Indicator of Chronic Anthropogenic Stress in Bats (Mammalia: Chiroptera)

Abstract

Exposure to chronic stressors has negative impacts on wild animals. Heightened levels of glucocorticoid hormones commonly are measured to test for exposure to stress. Due to the fast-changing nature of circulating levels of glucocorticoids, the neutrophil:lymphocyte ratio, which increases in response to stress more slowly than glucocorticoids, may be a more appropriate indicator of chronic stress. For this investigation, I first tested levels of cortisol and neutrophil:lymphocyte ratios of big brown bats (Eptesicus fuscus) and confirmed that cortisol and, in females, neutrophil:lymphocyte ratios increase after exposure to stressors. I then examined neutrophil:lymphocyte ratios and indexes of body condition of Myotis lucifugus, M. septentrionalis, and M. sodalis from two types of sites: those that were and those that were not impacted by anthropogenic disturbances. Neutrophil:lymphocyte ratios were significantly higher in reproductively active M. septentrionalis from impacted habitats (impacted ¯X= 0.40, unimpacted ¯X= 0.18), but did not differ significantly in other groups. Indexes of body condition were significantly lower at impacted sites for female M. sodalis. Other females were not significantly different, but indexes of body condition for male M. septentrionalis were significantly greater in impacted sites. Although results were inconsistent and sometimes conflicting, significant differences in neutrophil:lymphocyte ratios and indexes of body condition suggest that anthropogenic disturbances have the potential to act as stressors that can affect health of bats, and warrant further investigation into their effects on neutrophil:lymphocyte ratios.