Variance of Carotid-Rete-Mediated Selective Brain Cooling Across Aridity Indices

Abstract

Species-environment interactions are integral to survivorship, especially when those environments test the extremes of organismal physiology. Large-bodied (>50kg) mammals, specifically artiodactyls and feliform carnivores, possess a specialized physiology known as carotid-rete-mediated selective brain cooling (CR-SBC), which has been established to be selectively advantageous in environments where water availability is limited and risk for dehydration is high. In this study, we investigate whether CR-SBC provides a release from physiological constraint imposed by the environment, specifically aridity. Using 18O values from tooth enamel as a proxy for water metabolism, we model the range in variance across 1265 individuals from species that possess a carotid rete against those without from three different environmental categories – arid, dry subhumid, and humid – using a non-parametric ANOVA. The results of the analysis indicate there is a comparatively higher, and statistically significant, amount of variance of 18O in mammals possessing CR-SBC than those without, especially within arid climates, that begins to equalize as environmental water availability increases. As environments become increasingly arid, understanding which species are more vulnerable to shifts in climate becomes more pertinent. The presence of CR-SBC provides a clear, binary feature by which to measure the relationship between the environment and species survivorship under varying levels of water availability, and is useful in informing and improving conservation tools, such as physiological distribution models.