CHELA FUNCTION, MORPHOMETRIC MATURITY, AND THE MATING EMBRACE IN MALE SNOW CRAB, CHIONOECETES-OPILIO

Behavior and chela function associated with precopulatory clasping in morphometrically mature (MM) and morphometrically immature (MI) male snow crab, Chionoecetes opilio, were compared. MM males clasp receptive females more readily and for a more protracted period than MI males. Moreover, smaller MM males were more successful in initiating and maintaining precopulatory holds than larger MI males. These differences in clasping behavior cannot be attributed to differences in chela function, as the force developed is sufficient for clasping in both cases. The output force of the MM chela is, however, significantly higher than for MI chela because of their higher mechanical advantage and muscle stress and the presence of a larger closer muscle. Nor are differences in clasping behavior due to the fiber composition of the chela closer muscle which is composed of slow fibers in both morphotypes. These fibers are highly differentiated in their sarcomere lengths and enzymatic (ATPase and NADH-diaphorase) profiles which allow them to provide slow, powerful, and sustained contractions suited to precopulatory clasping. Since chela morphology and closer muscle composition appear adapted to precopulatory clasping in both morphotypes, other factors, most likely neurohormonal, may make MM males clasp more readily than their MI conspecifics.