Establishment and maintenance of claw bilateral asymmetry in snapping shrimps

Abstract

AbstractThe paired asymmetric chelae, or claws, in snapping shrimps, Alpheus heterochelis, differ in form and function; the major, or snapper, claw is grossly enlarged, has a hammer and socket, and functions in agonistic 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 differentiate on a random basis into a snapper and a pincer claw by the sixth juvenile stage. Removal of one of the paired claws in the third or fourth juvenile stage results in the intact claw developing into a snapper, 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 pincer‐to‐snapper claw may limit the newly regenerating claw to a pincer type, we observed the effects of closer muscle tenotomy and nerve lesions 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 its innervation is otherwise intact, a pincer claw regenerates similar to the control animals. However, with radical tenotomy in which the tendon is removed from the claw and the closer muscle and its innervation is severely disrupted, either a pincer or snapper claw regenerates. Lesioning of the large nerve 2 by itself or together with the small nerve 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 snapper site. Thus, neural influences from the transforming pincer‐to‐snapper claw restrict regeneration of the contralateral claw to a pincer type thereby ensuring bilateral asymmetry in adult shrimps. © 1994 Wiley‐Liss, Inc.