Autotomy and recovery in the snapping shrimp, Alpheus angulosus McClure, 2002 (Caridea: Alpheidae)

Abstract

Snapping shrimps (Alpheus spp.) exhibit extreme asymmetry of the chelae, presenting a large snapper and a small pincer, which are used for different behaviors. Like most crustaceans, snapping shrimps are able to autotomize, or drop, limbs when threatened. Although some limbs can be regenerated following autotomy, when the snapper is autotomized, the shrimp undergoes claw reversal, growing a new pincer at the site of the autotomized snapper and transforming the previous pincer into a new snapper over a series of molts. Although autotomy is costly in terms of loss of function and limb re-growth, failing to autotomize a limb could be lethal. We document the breakage plane of Alpheus angulosus (McClure, 2002) and examined variation in "drop latency," the latency to autotomize the snapper claw in response to a standardized physical threat. We measured drop latency of mature snapper claws (i.e. with morphological features typical of adult snappers not recently autotomized) in a large cohort of the shrimp (N = 93). We found autotomy to be dependent on threat intensity rather than threat duration among all shrimp. Specifcally, autotomy occurrences were distributed in clusters around threat intensity changes, rather than normally distributed throughout threat time. We also found signifcantly longer drop latency in males than females, suggesting a greater cost of mature snapper autotomy in males (P = 0.004). After initial snapper autotomy, we also measured latency to autotomize the transforming claw based on molt stage. Transforming claws exhibited signifcantly shorter average drop latency than autotomy of mature snappers (P = 0.008). Our assessment of the behaviors of the autotomy of mature and transforming claws provides insight into the costs of autotomy relative to claw value, as well as the evolutionary costs of autotomy and claw transformation in snapping shrimps.