Sexual selection often results in males exhibiting exaggerated traits (e.g. bright colors, elaborate appendages) to attract potential mates and in some cases to also use as a weapon. These traits, however, can impose costs, such as an increase in energy expenditure and a decrease in locomotor performance, which could decrease foraging efficiency and increase an individual's vulnerability to predators. We examined the effect of the enlarged claw in male fiddler crabs Uca pugilator on ecologically relevant performance measures. We measured locomotor performance and kinematics during horizontal, uphill and downhill movements. Speed and stride mechanics were measured for clawed males, males after the claw was removed, and females while running on level (0°), uphill (15 and 30°) and downhill (−15 and −30°) slopes. Endurance capacities were measured on all crabs on horizontal and uphill inclines. Though claw removal had no significant effect on horizontal speeds, removal of the major claw significantly increased uphill speeds of male fiddler crabs at 15 and 30°inclines. Generally, as incline increased, the difference in performance between males with the enlarged claw and those with the claw removed increased. We also found that clawed males exhibit slower downhill speeds compared to clawless males and that claw removal significantly enhanced endurance on all inclines. This study indicates that an assessment of movement on level surfaces alone may not be entirely ecologically relevant when determining the actual costs of sexually selected ornaments.

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.

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Despite the limited mobility of freshwater mussels, locomotion, especially burrowing, may be a critical part of their ecology. The effects of temperature on burrowing activities in freshwater mussels have not received much attention. In the laboratory, we studied the effects of three temperatures (ca. 10, 20, and 30 C) on mussel burrowing behaviors and performance. Behaviors assessed include latency to valve opening, latency until the foot becomes extended, and latency until burrowing. We also quantified burrowing performance by measuring burrowing duration. Mussels were significantly more likely to extend their foot and ultimately burrow at the highest experimental temperature. Burrowing performance was not significantly impacted, with burrowing duration being largely unaffected by temperature. This pattern suggests a hypothetical mechanism, whereby if some temperature threshold is reached that allows burrowing, the animal burrows normally. If that threshold is not attained, the mussel will not explore its environment nor burrow. The implications of this work are important to mussel biology and conservation because the thermal regimes of aquatic systems are changing with other global temperatures and smaller-scale effects are common, such as alteration of thermal regimes due to the outflow from dams. If mussels in these systems are affected they are likely, in turn, to affect community and ecosystem ecology in their native habitats.

Arboreality is widespread in multiple lineages of snakes and these habitats are important for foraging, escaping predators, and thermoregulation for many species. However, very little is known about factors influencing the arboreal locomotor abilities of snakes. Arboreal performance was assessed in a semi-arboreal snake (Elaphe guttata) using an artificial perch apparatus. Locomotor velocity, body posture, and balance was measured during movement on three perch diameters (3, 6, 10-cm) at three temperatures (10, 20, 30 degrees C). Velocities attained by E. guttata on perches are much slower than those of terrestrial lateral undulation and swimming and somewhat slower than concertina velocities recorded in other species across the same experimental temperatures. At higher temperatures, faster speeds were associated with a more elongated posture. At lower temperatures, snakes displayed a more looped body posture, but still fell more often than at higher temperatures. Our results suggest that temperature has a large influence on both balance and movement by snakes on perches. Although there were no differences in velocities resulting from perch diameter, snakes fell more often from thicker perches. This differs from arboreal velocities attained by limbed vertebrates, which decrease with decreasing perch diameter, suggesting that snakes have a size-relative advantage over limbed animals, such as lizards, when traversing a network of narrow branches. Future studies investigating arboreal locomotion among snakes that vary both phylogenetically and morphologically are needed to assess the potential benefits of limblessness in complex, three-dimensional environments.