Meeting Abstract
The plagiopatagiales proprii are an array of muscles hypothesized to modulate movement of the armwing membrane and prevent excessive billowing during flight in bats. EMG recording demonstrates these muscles activate during the downstroke, but their mechanical role remains uncertain. To improve our understanding of their function, we recorded high-speed videos of three bats flying in a wind tunnel before and after nanoliter injections of diluted botulinum toxin A (or Botox®) into the plagiopatagiales proprii, causing temporary muscle paralysis without loss of sensation. Surprisingly, bats were only capable of sustained flight in the presence of a headwind after injection. Measurements of membrane motion and camber were made from 3D time-resolved point cloud reconstructions. Following loss of muscle function, kinematic parameters such as flapping amplitude and frequency changed modestly, but abduction of the fifth digit decreased substantially; this contrasted with our expectation that bats would increase extension at wing joints to maintain membrane tension. At comparable flight speeds, the temporal fluctuation in the membrane deformation, as monitored at a representative point in the mid-armwing, increased after injections, particularly during the first third of downstroke. In addition, the variance in the spanwise camber of the wing increased and qualitatively resembles the control case at low flight speed. The functional implications of these measurements and their relation to the loss of plagiopatagiales activity remains to be examined in more quantitative detail.
