Tissue Oxidative Ecology along an Aridity Gradient in a Mammalian Subterranean Species

Abstract

Climate change has caused aridification which can alter habitat vegetation, soil and precipitation profiles potentially affecting resident species. Vegetation and soil profiles are important for subterranean mole-rats as increasing aridity causes soils to become harder and geophytes less evenly distributed, and the inter-geophyte distance increases. Mole-rats obtain all water and dietary requirements from geophytes, and thus digging in harder soils may amplify stressors (hyperthermia, dehydration- or exercise-induced damage). This study assessed the oxidative status of the wild common mole-rat along an aridity gradient (arid, semi-arid and mesic). Kidney and liver oxidative markers, including total oxidant status (TOS), total antioxidant capacity (TAC), oxidative stress index (OSI), malondialdehyde (MDA) and superoxide dismutase (SOD) were measured. Liver oxidative status did not demonstrate any significance with the degree of the aridity gradient. Aridity affected the TAC and OSI of the kidney, with individuals in the most arid habitats possessing the highest TAC. The evolution of increased group size to promote survival in African mole-rats in arid habitats may have resulted in the additional benefit of reduced oxidative stress in the kidneys. The SOD activity of the kidneys was higher than that of the liver with lower oxidative damage, suggesting this species pre-emptively protects its kidneys as these are important for water balance and retention.

New insights into morphological adaptation in common mole‐rats (Cryptomys hottentotus hottentotus) along an aridity gradient

“…The roles of the kidney include water regulation and filtration, and detoxification of substances absorbed by the digestive system (Brzoska et al., 2003 ). Greater kidney mass could indicate links to physiological responses to heat and dehydration such as increased water regulation and water turnover, as well as a greater ability for water retention which can be utilised during periods of stress, starvation, and dehydration (Jacobs et al., 2020 , 2022 ). Other rodent and mole‐rat studies have explored the differences in kidney mass, size, function, and metabolism in arid and mesic regions, with similar findings (Al‐Kahtani et al., 2004 ; Jackson et al., 2004 ; Jacobs et al., 2022 ).…”

“…Greater kidney mass could indicate links to physiological responses to heat and dehydration such as increased water regulation and water turnover, as well as a greater ability for water retention which can be utilised during periods of stress, starvation, and dehydration (Jacobs et al., 2020 , 2022 ). Other rodent and mole‐rat studies have explored the differences in kidney mass, size, function, and metabolism in arid and mesic regions, with similar findings (Al‐Kahtani et al., 2004 ; Jackson et al., 2004 ; Jacobs et al., 2022 ). Many bulbs found in the Northern Cape, where the arid populations in this study occur, have been found to be toxic, such as the bulbs of the Drimia plants (Manganyi et al., 2021 ).…”

“…The retention of pelage and the effects on thermoregulation are not currently understood. Common mole‐rats, like all African mole‐rats, do not drink free‐standing water but rely on their food source of underground geophytes to obtain all their water requirements (Jacobs et al., 2022 ). Aridity has been established to influence metabolism and water uptake in mammals, with species in arid environments exhibiting lower metabolic rates and water loss than mesic‐adapted species (Tieleman et al., 2003 ).…”

“…Aridity has been established to influence metabolism and water uptake in mammals, with species in arid environments exhibiting lower metabolic rates and water loss than mesic‐adapted species (Tieleman et al., 2003 ). Oxidative stress in mesic common mole‐rat populations has been detected in the kidneys when compared to arid populations and the low levels of oxidative stress in arid populations may infer these individuals have mechanisms to combat hyperthermia and dehydration, and potentially exercise‐induced damage due to the more compact soil (Jacobs et al., 2022 ). Thus, precipitation and temperature, as well as the different resulting soil structure may exert differing selection pressures on individuals found in arid environments, compared to non‐arid.…”

Redox Metabolism in Ecophysiology and Evolution

“…Jacobs et al [ 5 ] investigated the impact of aridification on wild common mole rats and their oxidative status along an aridity gradient. Liver oxidative status showed no significant change with aridity levels.…”