Locomotor endurance and oxygen consumption of harvestmen

Animal movements are highly constrained by morphology and energetics. In addition, predictable bodily damage can constrain locomotion even further. For example, for animals moving on land, losing legs may impose additional costs. We tested if losing legs affects the distance travelled over time (endurance) and the metabolic costs of locomotion (oxygen consumption) in Nelima paessleri harvestmen. These arachnids voluntary releases legs (i.e., autotomy) in response to predation attempts. We used flow-through respirometry as animals moved on a treadmill inside a sealed chamber. We found that endurance decreased gradually with an increasing number of legs lost. Interestingly, oxygen consumption increased only for harvestmen that lost three legs, but not for individuals that lost only a single leg. These results have different ecological and evolutionary implications. Reduced endurance may impair an animal’s ability to continue moving away from potential predators, while increased oxygen consumption makes movement costlier. Our findings suggest that individuals have a threshold number of legs that can be lost before experiencing measurable energetic consequences. Overall, our findings illustrate how animals respond to morphological modifications (i.e., damage) that affect the physiology of locomotion.

Methods
We measured the endurance and the metabolic costs of transportation using oxygen flow-through respirometry as Nelima paessleri harvestmen moved on a treadmill inside a sealed chamber.