Functional implications of supercontracting muscle in the chameleon tongueretractors

Chameleons capture prey items using a ballistic tongue projection mechanism that is unique among lizards. During prey capture, the tongue can be proje cted up to two fall body lengths and may extend up to 600 % of its resting length. Being ambush predators, chameleons eat infrequently and take relati vely large prey. The extreme tongue elongation (sixfold) and the need to be able to retract fairly heavy prey at any given distance from the mouth are likely to place constraints on the tongue retractor muscles. The data exam ined here show that in vivo retractor force production is almost constant f or a wide range of projection distances. An examination of muscle physiolog y and of the ultrastructure of the tongue retractor muscle shows that this is the result (i) of active hyoid retraction, (ii) of large muscle filament overlap at maximal tongue extension and (iii) of the supercontractile prop erties of the tongue retractor muscles. We suggest that the chameleon tongu e retractor muscles may have evolved supercontractile properties to enable a substantial force to be produced over a wide range of tongue projection d istances. This enables chameleons successfully to retract even large prey f rom a variety of distances in their complex three-dimensional habitat.