Abstract:
Heat waves are known for their disastrous mass die-off effects due to dehydration and cell
damage, but little is known about the non-lethal consequences of surviving severe heat
exposure. Severe heat exposure can cause oxidative stress which can have negative consequences
on animal cognition, reproduction and life expectancy. We investigated the current
oxidative stress experienced by a mesic mouse species, the four striped field mouse,
Rhabdomys dilectus through a heat wave simulation with ad lib water and a more severe
temperature exposure with minimal water. Wild four striped field mice were caught between
2017 and 2019. We predicted that wild four striped field mice in the heat wave simulation
would show less susceptibility to oxidative stress as compared to a more severe heat stress
which is likely to occur in the future. Oxidative stress was determined in the liver, kidney and
brain using malondialdehyde (MDA) and protein carbonyl (PC) as markers for oxidative
damage, and superoxide dismutase (SOD) and total antioxidant capacity (TAC) as markers
of antioxidant defense. Incubator heat stress was brought about by increasing the body temperatures
of animals to 39–40.8˚C for 6 hours. A heat wave (one hot day, followed by a 3-
day heatwave) was simulated by using temperature cycle that wild four striped field mice
would experience in their local habitat (determined through weather station data using temperature
and humidity), with maximal ambient temperature of 39˚C. The liver and kidney
demonstrated no changes in the simulated heat wave, but the liver had significantly higher
SOD activity and the kidney had significantly higher lipid peroxidation in the incubator experiment.
Dehydration significantly contributed to the increase of these markers, as is evident
from the decrease in body mass after the experiment. The brain only showed significantly higher lipid peroxidation following the simulated heat wave with no significant changes following
the incubator experiment. The significant increase in lipid peroxidation was not correlated
to body mass after the experiment. The magnitude and duration of heat stress, in
conjunction with dehydration, played a critical role in the oxidative stress experienced by each tissue, with the results demonstrating the importance of measuring multiple tissues to
determine the physiological state of an animal. Current heat waves in this species have the
potential of causing oxidative stress in the brain with future heat waves to possibly stress the
kidney and liver depending on the hydration state of animals.
