DIGITAL MORPHOLOGY IN THE CHIROPTERA - THE PASSIVE DIGITAL LOCK

Most bats hang from their hindlimb digits for extended periods of time during a variety of activities. Many species possess digital locking mechanisms consisting of modified digital flexor tendons and tendon re tinacula. When the digits are flexed, scales or tubercles on the tendo n surface engage transverse ribs which invest the inner surfaces of th e tendon retinacula. This locks the tendon in place and prevents the d igit from extending. Theoretically, by locking the digits during hangi ng, energy normally spent maintaining contraction of the digital flexo r muscles is conserved. In this study, digits from 10 species of bats from 5 families were examined by dissection and scanning electron micr oscopy. Variation in digital morphology was observed in species that e xhibit ecological diversity. It is proposed that hibernation and body weight are important selection pressures for possession of the passive digital lock. In nonhibernating species the mechanism may be present, modified or absent. The passive digital lock is absent in the vampire bats, a group whose feeding habits require substantially altered form s of locomotion. It is hypothesized that the passive digital lock has helped enable many species of bats to occupy habitats inaccessible to most other animals and that species lacking it may exhibit alternative mechanisms that allow them to hang in an energy-efficient manner.