Neutrophil: Lymphocyte Ratios as a Measure of Chronic Stress in Populations of the Hellbender (Cryptobranchus alleganiensis) across a Habitat Quality Gradient

Litmer, Allison

ABSTRACT: Amphibians are currently facing widespread population declines, primarily due to the introduction of anthropogenic stressors. Anthropogenic stressors have the potential to alter ecosystem dynamics and elicit long-term physiological responses that could hinder population viability. Current metrics of population viability rely heavily on demographics, population fluctuation, and degree of isolation. Physiological parameters, such as stress-response proxies, offer a new scale for population assessment, providing an explanation of the mechanism causing population declines. Implicating a method of assessing chronic stress, such as white blood cell counts, specifically neutrophil: lymphocyte (N: L) ratios, may provide a metric that can be rapidly assessed and related back to microhabitat characteristics for management purposes. As a long-lived habitat specialist facing population declines, the hellbender (Cryptobranchus alleganiensis) is a good candidate species for applying N: L ratios to assess population viability. This study used N: L ratios in relation to microhabitat variables to assess chronic stress among populations, determine environmental variables correlated with stress, and assess the implication of N: L ratios, among wild hellbender populations. Of the microhabitat variables assessed, high conductivity, low pH and low dissolved oxygen, correlated with elevated N: L ratios. Additionally, N: L ratios significantly differed among hellbender populations, suggesting that varying habitat condition and environmental stressors influencing population viability are reflected by N: L ratios. Specifically, N: L ratio indicated populations of management concern that traditional methods failed to suggest. Viability assessments incorporating physiological parameters provide evidence of declining viability earlier than traditional methods, and suggest specific variables contributing to stress, allowing for better management strategy.