Terrestrial Birth and Body Size Tune UCP1 Functionality in Seals

Area of Science:

• Evolutionary biology
• Mammalian physiology
• Thermoregulation

Background:

• The molecular evolution of the heater protein UCP1 (Uncoupling Protein 1) offers insights into thermoregulatory strategies in mammals adapting to extreme environments.
• While fully aquatic mammals have lost UCP1, most semiaquatic seals retain functional UCP1 genes, with exceptions like large elephant seals.

Purpose of the Study:

• To investigate the UCP1 thermogenic activity in harbor seals and elephant seals.
• To understand the evolutionary pressures on UCP1 function in semiaquatic pinnipeds during adaptation to terrestrial birth.

Main Methods:

• Comparative analysis of UCP1 gene integrity and function in harbor seals and elephant seals.
• Assessment of UCP1 thermogenic activity, including repaired and truncated versions.

Main Results:

• Harbor seal UCP1 exhibits potent thermogenic activity, comparable to terrestrial mammals, crucial for neonatal survival on land.
• Elephant seal UCP1 lacks thermogenic activity, even in repaired or truncated forms, indicating a complete loss of function.
• The evolutionary selection for UCP1 function in pinnipeds was outweighed by the extreme body size of elephant seals.

Conclusions:

• UCP1-dependent thermogenesis is vital for neonatal survival in smaller, semiaquatic mammals like harbor seals.
• Extreme body size in elephant seals led to the elimination of UCP1-dependent thermogenesis, suggesting alternative thermoregulatory strategies.