Spiders on a treadmill: influence of running activity on metabolic rates in Pardosa lugubris (Araneae, Lycosidae) and Marpissa muscosa (Araneae, Salticidae).

The CO2 release of the well-tracheated jumping spider, Marpissa muscosa, and the poorly tracheated, Pardosa lugubris, was tested while animals were running on a treadmill at three different speeds and under a selective elimination of lungs or tracheae. Thus, the influence of a well-developed tracheal system on the metabolism during physical exercise was examined. The CO2 release in intact animals increased with the running speed in both species. The costs of transport (COT) running at the maximal sustainable speed were nearly twice as big in M. muscosa as in P. lugubris. Elimination of one lung by sealing resulted in reduced COT and running times, and increasing anaerobic proportions in metabolism. Effects were greater in P. lugubris than in M. muscosa, indicating that tracheae compensate partly for the lacking lung capacity. Sealing of the tracheae in M. muscosa reduced the COT and the running times only at the highest speed. Results indicate that tracheae in M. muscosa support the aerobic metabolism only at the most intense physical exercise. At low and medium activity, tracheae may play their main role in the local supply of organs that are not involved in running activity.