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

View Article: PubMed Central - PubMed

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.

No MeSH data available.


Related in: MedlinePlus

The relationship between body weight and pinching force of the coconut crabs.Blue and red indicate male and female, respectively. Black line is a regression line using the combined data of both sexes.
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pone.0166108.g002: The relationship between body weight and pinching force of the coconut crabs.Blue and red indicate male and female, respectively. Black line is a regression line using the combined data of both sexes.

Mentions: The closer muscle fiber sarcomere length was measured in the larger left claw of a voucher coconut crab specimen (OCF-Cr00051 deposited in the Okinawa Churashima Foundation, 51.3 mm ThL, male, preserved 70% ethanol solution after 10% formalin fixation). The muscle tissues (dorsal-ventral, mid-way along the manus) were embedded in paraffin, sectioned to 7 μm, and stained with phosphotungstic acid hematoxylin (PTAH) for histological observation. Single sarcomere lengths from a fiber on the slide were measured using a digital microscope (OLYMPUS, BX53). Muscle stress in this specimen was calculated using the following formula: S = F/Asin2θ, which was obtained in a previous study [10], where F is the force applied to the base of the dactyl, estimated from the relationship between the actual pinching force and body weight (Fig 2), and the mechanical advantage (Lber/L1, Fig 1C). The value of A (the area of one side of the closer apodeme) and θ (the mean angle of the fiber attached the closer apodeme) of the claw specimen were directly measured.


A Mighty Claw: Pinching Force of the Coconut Crab, the Largest Terrestrial Crustacean
The relationship between body weight and pinching force of the coconut crabs.Blue and red indicate male and female, respectively. Black line is a regression line using the combined data of both sexes.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120803&req=5

pone.0166108.g002: The relationship between body weight and pinching force of the coconut crabs.Blue and red indicate male and female, respectively. Black line is a regression line using the combined data of both sexes.
Mentions: The closer muscle fiber sarcomere length was measured in the larger left claw of a voucher coconut crab specimen (OCF-Cr00051 deposited in the Okinawa Churashima Foundation, 51.3 mm ThL, male, preserved 70% ethanol solution after 10% formalin fixation). The muscle tissues (dorsal-ventral, mid-way along the manus) were embedded in paraffin, sectioned to 7 μm, and stained with phosphotungstic acid hematoxylin (PTAH) for histological observation. Single sarcomere lengths from a fiber on the slide were measured using a digital microscope (OLYMPUS, BX53). Muscle stress in this specimen was calculated using the following formula: S = F/Asin2θ, which was obtained in a previous study [10], where F is the force applied to the base of the dactyl, estimated from the relationship between the actual pinching force and body weight (Fig 2), and the mechanical advantage (Lber/L1, Fig 1C). The value of A (the area of one side of the closer apodeme) and θ (the mean angle of the fiber attached the closer apodeme) of the claw specimen were directly measured.

View Article: PubMed Central - PubMed

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.

No MeSH data available.


Related in: MedlinePlus