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

Abstract

Amphibians are currently facing widespread population declines, primarily due to the introduction of anthropogenic stressors, which have the potential to alter ecosystem dynamics and elicit long-term physiological responses resulting in overall population declines. Population assessments typically rely upon genomics, demography, and geographic isolation; however, when physiological parameters are included, mechanistic explanations for population declines can be determined. Rapid population assessments that can be related to specific microhabitat characteristics for management purposes can be achieved by implementing a chronic stress proxy, such as neutrophil: lymphocyte (N:L) ratios. As a long-lived habitat specialist, facing dramatic population declines with state and federally protected populations, the Hellbender (Cryptobranchus alleganiensis) is a good candidate species for applying N:L ratios to assess population vulnerability and habitat quality. This study used N:L ratios as a proxy of chronic stress among Hellbender populations to determine environmental variables potentially correlated with chronic stress. Additionally, comparisons of N:L ratios were made among Hellbender populations to examine applicability of this method for assessing amongpopulation differences. Of the microhabitat variables assessed, high conductivity, low pH, and low dissolved oxygen correlated with elevated N:L ratios. In addition, N:L ratios differed significantly among Hellbender populations, which suggests the utility of N:L ratios as an indicator of population-level differences. Specifically, where traditional methods lack the ability to detect concerns, physiological assessment suggested certain populations may be of concern in regard to experiencing chronic stress. Including physiological parameters in viability and vulnerability assessments more frequently, such as the one described here, can provide evidence of population concerns earlier than traditional methods, and allow for better management strategy by elucidating specific environmental variables contributing to stress.

The habitat quality paradox: loss of riparian forest cover leads to decreased risk of parasitism and improved body condition in an imperiled amphibian

“…While we did not evaluate correlations between N:L ratios and water quality directly, WsRp forest is positively correlated with water quality in our system ( Supplementary Figure S1 ). Thus, the lack of a negative association between WsRp forest and WBC PC1 in our study contrasts somewhat with findings of Litmer et al (2020) , who reported an increase in hellbender N:L ratios in response to degraded water quality. One possible explanation for this contrast could be that parasite effects simply overwhelmed any effects of altered abiotic habitat conditions in our systems.…”

“…For example, we found that N:L ratios and eosinophils were often co-elevated, which is indicative of parasitic infection ( Hopkins et al , 2016 ), while a typical response to glucocorticoid secretion is characterized by increasing N:L ratios but a decline in eosinophils ( Davis et al , 2008 ; Falso et al , 2015 ). Otherwise, mean monthly N:L ratios observed in our study between April and August (range: 0.28–0.66; Supplementary Table S1 ) were similar to those reported for most sites sampled by Litmer et al (2020) , which only rarely exceeded 1.0, and thus collectively suggest that few if any of the sub-populations sampled in either study exhibited signals of true physiological stress (i.e. N:L ratio > 1.0; Davis and Maerz, 2022 ).…”

Pig Slaughter Operators’ Perception of Stunning Benefits: A Comparative Analysis of Electrical and Captive Bolt Effectiveness

“…Pre-slaughter stress can affect postmortem muscle metabolism and meat quality, leading to increased levels of catecholamines and creatinine kinase in the body, rapid glycolysis, and lactic acid buildup in the meat (Bourguet et al, 2011;Pisestyani et al, 2015). Animal stress levels can be measured using neutrophil-lymphocyte ratio (Litmer et al, 2020). Previous studies have shown that pigs executed with electrical stunning had a lower ratio, and this condition showed reduced stress (Anugrah et al, 2022), further supported by a decrease in superoxide dismutase level (Prayoga et al, 2020).…”