Meeting Abstract
Lizards are known to swim by tucking their limbs next to their body then undulating their body and tail. However, Basilisk lizards can run bipedally on water surfaces. Field observations in Southeast Asia revealed that house geckos rapidly locomote on the water’s surface quadrupedally. Here, we describe surface water locomotion in the non-aquatic house gecko (Hemidactylus frenatus, svl: 57.9±1.8mm, weight: 5.7±0.5g). While these lizards used typical undulatory motions at low velocities, we observed kinematics with similarities to Basilisk lizards when house geckos reached velocities higher than approximately 40 cm/s. At these velocities (62.8±9.7cm/s), all four limbs exit the water and stroke downwards creating air cavities, allowing geckos to lift their head and front-torso high out of the water. Similar to rapid terrestrial trotting, house geckos showed a stance (20.0±4.0ms) and swing (45.8±9.8ms) corresponding to a duty factor less than 0.5. We show that the height of the forelimb above the water is strongly correlated with forward velocity. This is likely due to the positive relationship between forelimb height and the magnitude of slap impulse. By analyzing the relationships of Bond, Reynolds and Weber Numbers, estimates using hydrodynamic models of maximum slap and stroke impulses predict that house geckos are incapable of producing forces large enough to lift their entire body weight out of the water to produce “true” water running. However, the upward forces produced still appear to benefit the animals by allowing them to move faster than regular swimming. Quadrupedal surface locomotion may have important behavioral consequences in nature.
