BEHAVIORAL, VENTILATORY, AND METABOLIC RESPONSES OF THE HYPOGEAN AMPHIPOD NIPHARGUS-VIREI AND THE EPIGEAN ISOPOD ASELLUS-AQUATICUS TO SEVERE HYPOXIA AND SUBSEQUENT RECOVERY

Tbe locomotory and ventilatory activities and the intermediary and ene rgy metabolism modifications of the hypogean amphipod Niphargus virei and the epigean isopod Asellus aquaticus were compared during severe h ypoxia (<0.03 kPa) and subsequent recovery. The aims of this study wer e (1) to determine why the subterranean species displayed a greater to lerance of hypoxia than A. aquaticus and numerous other epigean crusta ceans, (2) to confirm previous results obtained with the hypogean amph ipod Niphargus rhenorhodanensis and the epigean amphipod Gammarus foss arum, (3) to provide an interspecific comparison of epigean species in order to see if responses showed by epigean amphipods during hypoxia and recovery can be extended to epigean isopods, and (4) to better und erstand the ecological problems of the hypogean organism's survival an d perennation in subterranean habitats. Both organisms responded to lo ng-term experimental severe hypoxia with classical anaerobic metabolis m, characterized by a decrease in ATP and phosphagen, the use of glyco gen and glutamate, and the accumulation of lactate (with some alanine) . In addition, some accumulation of succinate was found in N. virei. L actate (and succinate for N. virei) was also largely excreted by both amphipods, which is unusual for the crustacea in general. Compared wit h A. aquaticus and most other epigean crustaceans, N. virei showed lar ge amounts of stored glycogen and arginine phosphate. These difference s in glycogen and phosphagen stores, and the ability to reduce glycoly tic flux and energetic expenditures linked to locomotion and ventilati on extended the survival of hypogean crustaceans under experimental an aerobiosis (LT(50) was 52.1 h for N. virei and 19.7 h for A. aquaticus during severe hypoxia at 11 degrees C). During recovery, both species displayed characteristic hyperventilation, slow locomotory activity, and predominantly aerobic metabolism. Asellus aquaticus excreted a lar ge part of the lactate accumulated during severe hypoxia, whereas N. v irei remetabolized it, as it had a higher lactate-derived glyconeogene sis capacity. The disposal of end products and replenishing of glycoge n, ATP, and phosphagen required more than 24 h for both organisms. Nip hargus virei showed a faster and more complete replenishment of ATP an d arginine phosphate levels than A. aquaticus. Data concerning locomot ory, ventilatory, and metabolic responses to hypoxia and subsequent re covery in N. virei and A. aquaticus are similar to those obtained with N. rhenorhodanensis and G. fossarum.