Abstract
Crustaceans can exert a greater force using their claws than many animals can with other appendages. Furthermore, in decapods, the chela is a notable organ with multifunctional roles. The coconut crab, Birgus latro, is the largest terrestrial crustacean and has a remarkable ability to lift weights up to approximately 30 kg. However, the pinching force of this crab’s chelae has not been previously investigated. In the present study, we measured the pinching force of the chelae in 29 wild coconut crabs (33–2,120 g in body weight). The maximum force ranged from 29.4 to 1,765.2 N, and showed a strong positive correlation with body mass. Based on the correlation between pinching force and body weight, the force potentially exerted by the largest crab (4 kg weight) reported in a previous study would be 3300 N, which greatly exceeds the pinching force of other crustaceans as well as the bite force of most terrestrial predators. The mighty claw is a terrestrial adaptation that is not only a weapon, which can be used to prevent predator attack and inhibit competitors, but is also a tool to hunt other terrestrial organisms with rigid exteriors, aiding in these organisms to be omnivores.
Highlights
Most decapod crustaceans possess well-developed chelae, which are typically used to capture, manipulate, and process prey, as well as for defense and aggressive intraspecific interactions and displays [1]
The scaling factor in the allometric equation for pinching force and body weight (BW) was 0.82 (Fig 2). This value was significantly greater than the predicted isometric scaling of pinching force against BW (a = 0.67 [11])
The maximum force exerted by major muscle groups usually ranges between 10 body mass-1/3 and 50 body mass-1/3 [11] (Fig 3)
Summary
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]. The chelae of decapods (e.g. Cancer spp.) can exert a greater pinching force relative to their body mass than other animals [2]. The coconut crab, Birgus latro, the largest terrestrial crustacean, has unique characteristics related to their phylogenetic position. The coconut crab shares a common ancestor with terrestrial hermit crabs, Coenobita spp., and has lost dependence on shells for the protection of the pleon in adult stages, and instead develops a calcified body [3]. Independence from shells removes restrictions on body size [4], and has possibly led to the development of new functions associated with their large claws
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