SELECTION ON LOCOMOTOR PERFORMANCE CAPACITY IN A NATURAL POPULATION OF GARTER SNAKES

Area of Science:

• Ecology
• Evolutionary Biology
• Herpetology

Background:

• Locomotor performance is a key trait influencing survival and fitness in many species.
• Understanding selection pressures on these traits is crucial for evolutionary studies.
• Garter snakes (Thamnophis sirtalis fitchi) provide a valuable model for studying these relationships due to their accessibility and observable behaviors.

Purpose of the Study:

• To investigate the relationship between locomotor performance and survivorship in a population of garter snakes.
• To identify which specific locomotor traits (burst speed, endurance, distance capacity) and body size metrics predict survival.
• To determine the patterns of natural selection acting on these traits across different age classes.

Main Methods:

• Mark-recapture study of garter snakes in Northern California.
• Measurement of snake length, mass, burst speed, treadmill endurance, and circular track crawling distance.
• Calculation of size-corrected residuals for mass and locomotor performance.
• Statistical analysis using randomization tests and regressions to assess trait-survival relationships.

Main Results:

• Birth body size (SVL) was the only significant predictor of neonatal survival, favoring larger individuals.
• For yearlings, greater burst speed and distance capacity residuals significantly increased survival, while intermediate mass residuals were also favored.
• For older snakes, greater burst speed residuals strongly predicted survival.

Conclusions:

• Locomotor performance traits, particularly burst speed and distance capacity, are significant drivers of survival in garter snakes.
• Selection pressures vary across age classes, with body size being critical for neonates and speed for older individuals.
• These findings highlight the adaptive significance of locomotor abilities in reptile populations.