Atmospheric oxygen levels affect mudskipper terrestrial performance: implications for early tetrapods.

Area of Science:

• Paleontology
• Evolutionary Biology
• Comparative Physiology

Background:

• The Japanese mudskipper (Periophthalmus modestus) is an amphibious fish with adaptations for terrestrial life.
• The Paleozoic Era saw significant fluctuations in atmospheric oxygen levels.
• Understanding these changes may illuminate the transition of vertebrates from water to land.

Purpose of the Study:

• To investigate the impact of varying atmospheric oxygen concentrations on the terrestrial performance and recovery of the Japanese mudskipper.
• To use the mudskipper as a model to infer how Paleozoic oxygen levels influenced early tetrapod evolution.

Main Methods:

• Testing mudskipper performance on a terrestrial treadmill under hyperoxia (35% O2), normoxia (21% O2), and hypoxia (7% O2).
• Measuring endurance, post-exercise oxygen consumption (EPOC), and recovery time to resting metabolic rate.
• Observing ventilatory movements associated with aerial respiration post-exercise.

Main Results:

• Endurance and EPOC increased with higher oxygen concentrations.
• Recovery time to resting metabolic rate did not differ significantly, but delayed oxygen debt repayment was observed in normoxia.
• Aerial respiration patterns normalized faster in higher oxygen conditions.

Conclusions:

• The Japanese mudskipper exhibits enhanced exercise capacity and quicker recovery under elevated oxygen levels.
• Increasing Paleozoic atmospheric oxygen likely supported greater aerobic capacity and terrestrial performance in early tetrapods.
• These conditions may have facilitated the diversification and expansion of vertebrates into terrestrial environments.