Physical constraints on thermoregulation and flight drive morphological evolution in bats

Area of Science:

• Ecology
• Evolutionary Biology
• Biophysics

Background:

• Organismal energy requirements are linked to body size and shape, influencing heat exchange and locomotion costs.
• Ecological patterns show body size varies with climate (e.g., larger endotherms in colder regions), but modeling this link from first principles is limited.
• Bat body size evolution deviates from other endotherms, likely due to flight's physical constraints on morphology.

Purpose of the Study:

• To develop a biophysical model investigating energy constraints on morphological evolution in bats.
• To explore how heat transfer and aerodynamic principles influence bat body shape.
• To understand why bats exhibit unique ecogeographical patterns compared to other mammals.

Main Methods:

• Developed a biophysical model integrating heat transfer and aerodynamic principles.
• Predicted optimal wing surface area to body mass (S-MR) ratio based on minimized energy costs.
• Conducted a comparative analysis of S-MR across 278 bat species.

Main Results:

• The model predicts that thermoregulation and flight costs set upper and lower limits on S-MR, creating an optimal ratio.
• Comparative analysis supports the model, showing bat S-MR evolves towards this optimum.
• Selection strength for optimal S-MR is higher in species with greater thermoregulation demands in cold climates.

Conclusions:

• Energy costs significantly modulate morphological evolution in bats, explaining their unique ecogeographical patterns.
• The study provides a framework for investigating macroecological patterns from fundamental biophysical principles.
• Findings contribute to understanding the long-standing debate on bats' conformity to general mammalian ecogeographical rules.