Pinching forces in crayfish and fiddler crabs, and comparisons with the closing forces of other animals

Abstract

The pinching forces of crustaceans are in many respects analogous to the biting forces of vertebrates. We examined the effects of body size and chelae size and shape, on the closing forces of the fiddler crab, Uca pugilator, and the crayfish, Procambarus clarkii. We hypothesized that the allometric relationships would be similar among species, and comparable to those reported for other decapod crustaceans. We further hypothesized that the scaling of the closing forces of crustaceans, with respect to body size and with the geometry of the pinching or biting structures, would be similar to that of vertebrates. We found that pinching forces increased with body mass, claw dimensions, and claw mass in U. pugilator, but only with claw height and claw mass in P. clarkii. Contraction time increased with body mass for both species combined, whereas contraction speed decreased. Pooled data for these and 17 other species of decapod crustacean revealed a positive correlation between the pinching force and body mass with a scaling exponent of 0.71. These data are remarkably comparable to the values on closing forces of vertebrate jaws, with the pooled data having a scaling exponent of 0.58, slightly below the value of 0.67 predicted for geometric similarity. Maximum closing forces vary tremendously among both crustaceans and animals in general, with body size and food habits being among the most important determining factors.

A Mighty Claw: Pinching Force of the Coconut Crab, the Largest Terrestrial Crustacean

“…According to a previous study, the reported maximum BW of the coconut crab is 4 kg [12]. Applying our allometric scaling equation, the pinching force of the coconut crab of 4 kg BW was estimated to be 3300 N. This force greatly exceeds that in all other crustacean species that have been reported [1, 2], as well as the bite force for the majority of modern terrestrial predators, other than alligators [13–14]. The maximum force exerted by major muscle groups (in terms of force / body weight) usually ranges between 10 body mass -1/3 and 50 body mass -1/3 [11] (Fig 3).…”

“…Most decapod crustaceans possess well-developed chelae, which are typically used to capture, manipulate, and process prey (e.g., crush), as well as for defense and aggressive intraspecific interactions and displays [1]. Pinching forces of decapod chelae vary greatly and are largely determined by the claw size [1].…”

“…Pinching forces of decapod chelae vary greatly and are largely determined by the claw size [1]. Notably, the chelae of decapods (e.g.…”

Interlocking of chelae is a key factor for dominance hierarchy formation in crayfish

“…During growth, the body proportions are similar, with the cephalothorax and abdomen being approximately equal; however, the chelae show positive allometry (Bovbjerg, 1956;Aiken and Waddy, 1992). There is a positive correlation between the pinching force and body length, between the pinching force and body mass, and also between chelae size and chelae force (Claussen et al, 2008;Wilson et al, 2009). Rutherfold et al (Rutherfold et al, 1995) showed that chela length was an important indicator of fighting ability in the crayfish Orconectes rusticus, as there was no significant difference in cephalothorax length but winners had significantly longer chelae than losers.…”

Functional morphology and bite performance of raptorial chelicerae of camel spiders (Solifugae)

“…Therefore, only pinch forces of crustaceans and scorpions have been studied experimentally in more detail (e.g. Taylor, 2000;Claussen et al, 2008;Van der Meijden et al, 2010;Van der Meijden et al, 2012) or estimated by biomechanical modeling in oribatid mites (Heethoff and Norton, 2009).…”