Summary1. Sexually selected structures with dual function of combat and display are likely to be honest signals of male quality to opponents and mates, but should be costly to produce and maintain. 2. Male fiddler crabs use a single greatly enlarged claw as both a weapon in agonistic contests with other males and an ornament to attract females for mating. Given the extreme size of this structure (up to half the total body mass), there is surprisingly little evidence for costs as predicted by theory. 3. We experimentally investigated several potential costs of the large claw to male sand fiddler crabs Uca pugilator . Mass-specific metabolic rates were significantly higher and treadmill endurance capacity significantly lower for males bearing an intact major claw compared with those without. 4. In contrast, presence of the claw did not affect maximal sprint speeds, suggesting that the massive structure does not compromise the ability of male crabs to evade predators. These counterintuitive results conform to recent theoretical models of energy costs of locomotion. 5. Our study provides empirical support for a key assumption of sexual selection theoryenergetic and endurance-related locomotor costs incurred while bearing this ornamental weapon act in opposition to sexual selection favouring larger claws.

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Over the period 1953–1979, a battery factory on the Hudson River in New York released ≈53 tons of cadmium (Cd) and nickel hydride wastes into Foundry Cove. The most common aquatic benthic species, the oligochaete Limnodrilus hoffmeisteri , rapidly evolved resistance to Cd. The capacity for detoxification and internal storage of Cd resulted in a strong potential for trophic transfer of Cd through the aquatic food web. As a result of United States Superfund legislation, a major remediation effort in 1994–1995 removed the majority of the Cd, thereby removing the selective force for resistance. The cleanup of this cove resulted in the maintenance of resistant forms but then there ensued a rapid loss of resistance in ≈9–18 generations, showing the potential for ecological restoration to rapidly reduce the potential for trophic transfer of Cd through the ecosystem. This study demonstrates a genetic approach to the study of ecological restoration and connects a genetic indicator of restoration to transfer of toxic metals through ecosystems.

Summary1. Previous evidence demonstrates that closing force decreases proportionally as fiddler crab claw size increases. Larger crabs do have greater absolute closing force, but less than would be expected if claw proportions were isometric. In the Mud Fiddler Crab, Uca pugnax , this is explained by a decrease in mechanical advantage with increasing claw size. 2. We here re-measure mechanical advantage with a more direct method than used previously; the relationship of mechanical advantage to claw size was similar to the older indirect measure. Because the fiddler crab claw is a simple lever, we predicted that the observed decline in closing force should be compensated by a proportional increase in closing speed. 3. We tested this hypothesis using high-speed video to observe crabs closing their major claws spontaneously under controlled conditions. Closing speed scaled positively to claw length as predicted, and the value of the exponent conformed to expectation from a simple biomechanical model. 4. Evolution of the fiddler crab claw therefore involved a trade-off of closing force for closing speed. An adaptive explanation of relative weakening with increasing body size may lie in the increased ability to rapidly grasp an opponent, a crucial advantage in fiddler crab combat.