Subterranean Fishes of the World

6213

2023

Physiological and Biochemical Zoology

In press

In the face of increasing environmental temperatures, operative differences between mitochondrial function and whole-animal phenotypic response to environment are underrepresented in research, especially in subtemperate ectothermic vertebrates. A novel approach to exploring this connection is by examining model species that are genetically similar but have different whole-animal phenotypes, each of which inhabit different environments. The Mexican cavefish, Astyanax mexicanus, has two morphotypes; a surface form found in aboveground rivers, and an obligate cave-dwelling form. Each morphotype inhabits vastly different thermal and oxygen environments. Whole-animal and mitochondrial responses to thermal acclimation and oxidative stress (OS) with respect to increasing temperatures have not been previously determined in either morphotype of this species. Here, we chronically acclimated both morphotypes to three temperatures (14, 21, and 31 °C), so as to establish potential for acclimation and critical thermal maxima (CTmax) for either morphotype of this species. After measuring CTmax in all six cohorts, we additionally measured enzymatic antioxidant capacity (CAT, SOD and GPx activities), peroxyl scavenging capacity, and lipid peroxidation damage (LPO) in white epaxial muscle for each individual. We found a significant effect of acclimation temperature on CTmax (F = 29.57, p < 0.001), but we found no effect of morphotype on CTmax (F = 2.092, p = 0.162). Additionally, we found that morphotype had a significant effect on GPx activity, with the surface morphotypes having increased GPx activity compared with the cave morphotype (F = 6.270, p = 0.020). No other OS variable demonstrated significant differences. Increases in CTmax with chronic thermal acclimation to higher temperatures suggests some degree of phenotypic plasticity in this species that nominally occupies thermally stable environments. The decreased GPx activity in the cave morphotype may be related to decreased environmental oxygen concentration and decreased metabolic rate in this environmentally constrained morphotype compared with the surface-living counterparts.

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