Chiropteran tendon locking mechanism

Abstract

Rather than the usual mammalian scheme in which tendon and sheath surfaces provide as little friction as possible, the tendons and sheaths of many bats have a locking segment on the manual and pedal flexor tendon complex. This tendon locking mechanism (TLM) exists opposite the proximal phalanges of each toe and pollex of many bats. Its structure, similar to a ratchet mechanism, assists bats in hanging with little muscular effort. The third digit of the pelvic limb and the pollex of species representing 15 chiropteran families were studied to determine the presence or absence, morphology, and function of the TLM. Most of the species studied have a TLM consisting of a patch of tubercles on the ventral surface of the flexor tendon associated with the proximal phalanx of each pollex or toe. The sheath adjacent to this portion of the flexor tendon has a series of transverse folds or ridges, which, when engaged with the tubercles on the tendon, lock the tendon in place. The TLM is similar in megachiropterans and microchiropterans possessing it. The TLM is absent, however, in some of the microchiropterans studied, most notably in the phyllostomids. Since many birds have a TLM similar to that of bats, it is an excellent example of the convergent evolution of a feature brought about by similar functional pressures on birds and bats.

Hibernation energetics of free-ranging little brown bats

“…This supports the suggestion of Rojas and colleagues that, in certain circumstances, exceeding the 5% rule can substantially improve data quality without having a significant impact on the animals, as long as the ecology of the study species is taken into account (Rojas et al, 2010). The cost of carrying transmitters while roosting should be negligible for bats because little muscular effort is required for grasping the roosting substrate at rest (Quinn and Baumel, 1993). During hibernation, bats may also tolerate heavier transmitters than during the active season because they typically only fly for short distances to switch roosting locations or find water, tasks that require less manoeuvrability than foraging during the summer.…”

Friction between human finger flexor tendons and pulleys at high loads

“…Schaffer (1905) was the first to describe a ''SperrHemmvorrichtung'' in bats where the flexor tendon interacts and locks with the fibrous tendon sheath. Schutt (1993) investigated the mechanism more precisely in bats and Quinn and Baumel (1993) finally called it TLM and compared it in different bat species (chiropterans). A similar mechanism was described in climbing mammals by Schaffer (1905) and Haffner (1996), in birds by Quinn and Baumel (1990) and in dermoptera by Simmons and Quinn (1994).…”

“…The friction between tendon and pulley is that high that flexor muscle may completely relax. Unlocking is enabled by unloading the finger and by two elastic ligaments the one extending the DIP joint and the other pulling the conjoint tendon distally (Quinn and Baumel, 1993). Walbeehm and McGrouther (1995) compared the TLM with the anatomy and function of the human flexor tendon sheath and described a tendon compressing mechanism (TCM) where the FDP tendon is compressed circularly by the chiasma of the FDS tendon and the A2 pulley.…”

Touchdown to take-off: at the interface of flight and surface locomotion

“…Many aerial vertebrates, with a few exceptions, rely on hands and/or feet with claws for surface attachment. Furthermore, many perching birds and bats have specialized mechanisms in the feet to remain perched with low energy cost [60,61] [62][63][64]. Similarly, frogs may use the specialized peg-like projections on their toes for interlocking on rough surfaces [68].…”

“…Exceptions to these attachment trends include some bats and snakes. Certain bats, relatively large powered flyers, use wet adhesion to roost under leaves [61,116]. Snakes are unusual in that they use their flexible bodies to wrap around structures upon landing [76].…”