Selective breeding for high endurance running increases hindlimb symmetry

Area of Science:

• Evolutionary biology
• Comparative biomechanics
• Animal locomotion

Background:

• Morphological adaptations for cursoriality (running ability) in mammals are well-documented, often indicated by long limbs and high limb bone ratios.
• Enlarged femoral condyles have been proposed as an adaptation for endurance running in humans (Homo).
• The impact of locomotor appendage asymmetry on performance lacks rigorous evolutionary study.

Purpose of the Study:

• To investigate morphological adaptations associated with high voluntary wheel running using experimental evolution in mice.
• To test whether classical indicators of cursoriality evolve with increased activity levels.
• To examine the role of limb symmetry in locomotor performance.

Main Methods:

• Selective breeding of mice for high voluntary wheel running activity over multiple generations.
• Comparative analysis of hindlimb bone morphology (femur, tibia, metatarsals) between high-running and control lines.
• Measurement of limb bone lengths, ratios, and directional asymmetry.

Main Results:

• High-running mice did not evolve classical cursoriality indicators like longer limb bones or higher metatarsal/femur ratios.
• Significant evolution of larger femoral condyles was observed in high-running mice.
• Reduced directional asymmetry of hindlimb bones was a key adaptation in high-running mice.

Conclusions:

• Sustained high-speed locomotion may favor adaptations like enlarged femoral condyles and reduced limb asymmetry over classical cursoriality traits.
• Limb symmetry appears crucial for efficient and high-performance locomotion.
• These findings provide an evolutionary context for understanding adaptations related to endurance running.