ESTABLISHMENT AND MAINTENANCE OF CLAW BILATERAL ASYMMETRY IN SNAPPINGSHRIMPS

The paired asymmetric chelae, or claws, in snapping shrimps, Alpheus h eterochelis, differ in form and function; the major, or snapper, claw is grossly enlarged, has a hammer and socket, and functions in agonist ic displays, while the minor, or pincer, claw is small and slender and functions in burrowing and feeding. The paired claws are symmetrical and undifferentiated in the larval and early juvenile stages but diffe rentiate on a random basis into a snapper and a pincer claw by the six th juvenile stage. Removal of one of the paired claws in the third or fourth juvenile stage results in the intact claw developing into a sna pper, suggesting that differential use initially determines claw type. However, claw bilateral asymmetry may be altered in adults as removal of the snapper claw causes transformation of the existing pincer into a snapper while a new pincer regenerates at the old snapper site. To test the hypothesis that inhibitory influences from the transforming p incer-to-snapper claw may limit the newly regenerating claw to a pince r type, we observed the effects of closer muscle tenotomy and nerve le sions in the intact transforming claw on the type of claw regenerated at the old snapper site. With mild tenotomy in which the tendon is cut at its attachment to the moveable dactyl but the closer muscle and it s innervation is otherwise intact, a pincer claw regenerates similar t o the control animals. However, with radical tenotomy in which the ten don is removed from the claw and the closer muscle and its innervation is severely disrupted, either a pincer or snapper claw regenerates. L esioning of the large nerve 2 by itself or together with the small ner ve 1 (but not nerve 1 by itself) in the intact transforming claw also permits regeneration of either a pincer or snapper claw at the old sna pper site. Thus, neural influences from the transforming pincer-to-sna pper claw restrict regeneration of the contralateral claw to a pincer type thereby ensuring bilateral asymmetry in adult shrimps. (C) 1994 W iley-Liss, Inc.