Development of dependence on oxygen in embryo salamanders

Area of Science:

• Developmental Biology
• Environmental Physiology
• Comparative Physiology

Background:

• Understanding the physiological adaptations of developing organisms to environmental stressors like hypoxia and anoxia is crucial.
• Ambystoma (salamander) embryos and larvae represent a valuable model for studying developmental plasticity and stress tolerance.

Purpose of the Study:

• To quantify survival times of Ambystoma embryos and larvae under anoxic and hypoxic conditions across different developmental stages.
• To investigate the impact of developmental stage on physiological responses, including heart rate and oxygen consumption, during oxygen deprivation.

Main Methods:

• Exposure of Ambystoma embryos and larvae to controlled anoxia and hypoxia (3.8% oxygen) at 20°C.
• Measurement of survival times, heart rates (in situ and isolated), and oxygen uptake at various developmental time points.
• Comparison of physiological parameters between different developmental stages and oxygen conditions.

Main Results:

• Survival times in anoxia decreased sharply with age, from over 30 hours at 2 days post-fertilization to 4-2 hours at 14 days.
• Hypoxia survival showed similar age-related declines, appearing approximately 7 days later than anoxic effects.
• Heart rates decreased in both anoxia and hypoxia, with older larvae experiencing cardiac arrest; oxygen uptake diminished even at 11% oxygen, suggesting cellular limitations rather than delivery issues.

Conclusions:

• Ambystoma development leads to a significant decrease in tolerance to anoxia and hypoxia, primarily due to reduced cardiac function and oxygen utilization.
• Oxygen uptake appears limited by cellular metabolic capacity rather than oxygen delivery, even with the development of a circulatory system.
• Observed changes in anoxia tolerance show parallels with those in avian and mammalian embryos, suggesting conserved developmental responses to oxygen stress.