Sprint performance is linked to surface activity in scorpions
Aerobic capacity in arachnids is closely linked to considerable structural variation in their respiratory tracts. However, all scorpions are non-tracheated and have four pairs of book lungs, but they vary greatly in their locomotion patterns. Many non-burrowing species express short bursts of activity, while other species dig deep burrows over hours, suggesting more aerobically driven exercise. We hypothesized that locomotion in surface dwellers is more dependent on anaerobic ATP synthesis, and that this would be reflected in their exercise performance and functional adaptation to potential disruption of resting state homeostasis. We used an experimental design consisting of two surface-dwelling Buthidae species (Hottentot judaicus and Leiurus hebraeus), a burrowing buthid (Buthus Israelis) and two burrowing Scorpionidae (Scorpio fuscus and S. palmatus). Maximum running speed was higher for buthids, which were also more prone to fatigue than scorpionids. Higher respiratory exchange ratios recorded for buthids during activity and subsequent recovery indicated higher reliance on anaerobically powered locomotion compared to scorpionids. Our data show that faster removal of excess CO2 as a result of anaerobic exercise and hemolymph buffering in buthids is associated with significantly higher carbonic anhydrase activity in their hemolymph compared to scorpionids. Effective CO2 emissions can also contribute to lower respiratory water losses by buthids, and thus help to meet both biotic and abiotic challenges of surface existence, from which the scorpionid caves provide refuge.
