MANDIBLE MUSCLE-FIBERS IN ANTS - FAST OR POWERFUL

Ants use their mandibles for catching prey, cracking seeds, cutting le aves, or for the construction of nests and the tender care of brood. T he functional morphology of the mandibles reflect the species' adaptat ions to particular foraging habits and social life. The versatility an d specialization of the mandibles depend directly on the design and ph ysiology of the mandible closer muscles and their component fibers. A comparative video analysis of the closing movements of ant mandibles r evealed that the maximal velocity varies considerably among species. T he speed is correlated with the morphology of the mandible closer musc le, the largest muscle in ants. It is composed of two morphologically very distinct fiber types: long fibers with short sarcomeres (sarcomer e length approximately 2 mu m) showing all the structural attributes o f fast muscle fibers, and shorter fibers with longer sarcomeres (sarco mere length approximately 5 mu m) exhibiting the characteristics of sl ow and powerful fibers. Ants with fast-moving mandibles have a very hi gh proportion of fast closer fibers, whereas the muscles of ants that cannot perform fast mandible movements have only a few or no fast fibe rs at all. Fast fibers always attach directly to the solid apodeme, wh ile slow fibers often attach to thin apodeme threads. We suppose that the latter kind of fiber attachment is disadvantageous for fast contra cting fibers but helps the ants to make better use of the space in the head capsule.