Cuticle Strength and the Size-Dependence of Safety Factors in Cancer Crab Claws

Palmer, A. Richard; Taylor, Graeme; Barton, Anise

doi:10.2307/1542953

Cited by 26 publications

(21 citation statements)

References 44 publications

(20 reference statements)

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“…This is still lower than that of bites at the medial protrusion (7.2). Nevertheless, both safety factors accord with those of other animals weapons (2 -7 in crab claws [45,46], 3.4-10 in sheep horns [43]). If this behavioural muscle force modulation truly exists, then mechanosensors should be present in the mandibles.…”

Section: Finite-element Model: Bite Force Modulationmentioning

confidence: 63%

Finite-element modelling reveals force modulation of jaw adductors in stag beetles

Goyens

Soons

Aerts

et al. 2014

J. R. Soc. Interface.

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Male stag beetles carry large and heavy mandibles that arose through sexual selection over mating rights. Although the mandibles of Cyclommatus metallifer males are used in pugnacious fights, they are surprisingly slender. Our bite force measurements show a muscle force reduction of 18% for tip biting when compared with bites with the teeth located halfway along the mandibles. This suggests a behavioural adaptation to prevent failure. We confirmed this by constructing finite-element (FE) models that mimic both natural bite situations as well as the hypothetical situation of tip biting without muscle force modulation. These models, based on micro-CT images, investigate the material stresses in the mandibles for different combinations of bite location and muscle force. Young's modulus of the cuticle was experimentally determined to be 5.1 GPa with the double indentation method, and the model was validated by digital image correlation on living beetles. FE analysis proves to be a valuable tool in the investigation of the trade-offs of (animal) weapon morphology and usage. Furthermore, the demonstrated bite force modulation in male stag beetles suggests the presence of mechanosensors inside the armature.

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Section: Finite-element Model: Bite Force Modulationmentioning

confidence: 63%

Finite-element modelling reveals force modulation of jaw adductors in stag beetles

Goyens

Soons

Aerts

et al. 2014

J. R. Soc. Interface.

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“…And, like beetle horns, these structures can and do fail. Approximately 6% of wild crab populations have broken claws [34], and the incidence of fracture for leg and wing bones of mammals and birds ranges from 0.2 to 3% [37]. Thus, even structures with high measured safety factors are susceptible to mechanical failure under natural conditions.…”

Section: Discussionmentioning

confidence: 99%

Mechanical limits to maximum weapon size in a giant rhinoceros beetle

McCullough

2014

Proc. R. Soc. B.

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The horns of giant rhinoceros beetles are a classic example of the elaborate morphologies that can result from sexual selection. Theory predicts that sexual traits will evolve to be increasingly exaggerated until survival costs balance the reproductive benefits of further trait elaboration. In Trypoxylus dichotomus, long horns confer a competitive advantage to males, yet previous studies have found that they do not incur survival costs. It is therefore unlikely that horn size is limited by the theoretical cost -benefit equilibrium. However, males sometimes fight vigorously enough to break their horns, so mechanical limits may set an upper bound on horn size. Here, I tested this mechanical limit hypothesis by measuring safety factors across the full range of horn sizes. Safety factors were calculated as the ratio between the force required to break a horn and the maximum force exerted on a horn during a typical fight. I found that safety factors decrease with increasing horn length, indicating that the risk of breakage is indeed highest for the longest horns. Structural failure of oversized horns may therefore oppose the continued exaggeration of horn length driven by male-male competition and set a mechanical limit on the maximum size of rhinoceros beetle horns.

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“…Table 3). Crabs with larger, stronger claws should have a selective advantage, not only because these individuals have access to a wider range of prey types and sizes, but also because there is less risk of claw damage when attacking prey of any given size (Juanes & Hartwick 1990, Juanes 1992, Juanes & Smith 1995, Palmer et al 1999. Upper limits on claw size may be set by metabolic costs of maintenance or replacement or by allometric constraints associated with declining muscle stress as claw size increases (Taylor 2000(Taylor , 2001.…”

Section: Adaptive Change In Trophic Structuresmentioning

confidence: 99%

Biogeographic differences in claw size and performance in an introduced crab predator Carcinus maenas

Smith¹

2004

Mar. Ecol. Prog. Ser.

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Introduced predators must forage effectively to persist in new areas, and effective resource use is correlated with a predator's trophic (feeding) structures. The extent to which trophic morphology responds to spatial variation in prey resistance, and the time scale of that response, however, are not well understood. The introduced European green crab Carcinus maenas, which has expanded its range in the northwest Atlantic Ocean over the last century and encountered a latitudinal cline in prey armor, offers an ideal opportunity to test for such post-invasion changes. In rocky intertidal habitats in the Gulf of Maine, southern populations of the snail Littorina obtusata are better defended than northern populations. To test for correlated differences in claw size and prey defense, green crabs and common molluscan prey were collected at southern and northern sites in the Gulf of Maine. C. maenas are heterochelous, and analyses revealed that crusher claws of crabs collected in the south were significantly larger than those of crabs from the north after adjusting for carapace width. The size of the cutter claw, however, did not differ between regions. Shell weights for similarsized snails differed among sites for 3 of the 4 species examined, but did not differ by region. To test crushing performance, southern and northern crabs were presented with increasing sizes of southern or northern L. obtusata in the laboratory. For similar-sized individuals, southern crabs were able to crush significantly larger snails than northern crabs regardless of the geographic origin of the snails. Thus, patterns in claw size and performance strongly suggest trophic responses to geographic differences in prey armor. Rapid changes in trophic morphology could facilitate the spread of this invasive species and initiate an ecological arms race if both predator and prey respond ecophenotypically to each other.

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Cuticle Strength and the Size-Dependence of Safety Factors in Cancer Crab Claws

Cited by 26 publications

References 44 publications

Finite-element modelling reveals force modulation of jaw adductors in stag beetles

Finite-element modelling reveals force modulation of jaw adductors in stag beetles

Mechanical limits to maximum weapon size in a giant rhinoceros beetle

Biogeographic differences in claw size and performance in an introduced crab predator Carcinus maenas

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