ABSTRACT
Understanding animal thermal tolerance is crucial to predict how animals will respond to increasingly warmer temperatures, and to mitigate the impact of the climate change on species survival. Yet, the physiological mechanisms underlying animal thermal tolerance are largely unknown. In this study, we developed a method for measuring upper thermal limit (CTmax) in larval zebrafish (Danio rerio) and found that it occurs at similar temperatures as in adult zebrafish. We discovered that CTmax precedes a transient, heat-induced brain-wide depolarization during heat ramping. By monitoring heart rate, we established that cardiac function is sub-optimal during the period where CTmax and brain depolarization occur. In addition, we found that oxygen availability affects both locomotor neural activity and CTmax during a heat stress. The findings of this study suggest that neural impairment due to limited oxygen availability at high temperatures can cause CTmax in zebrafish.
Highlights
Larval zebrafish reach their critical thermal limit (CTmax) at similar temperature as adult zebrafish
Acute heat stress causes a brain-wide spreading depolarization near the upper thermal limit
CTmax precedes brain-wide depolarization
Heart rate declines at high temperatures but is maintained during CTmax and brain depolarization
Neural activity is impaired prior to CTmax and brain-wide depolarization
Oxygen availability in the water affects both CTmax and neural activity
Competing Interest Statement
The authors have declared no competing interest.