Numerous groundwater ecosystems are characterized by severely limited food supplies during most of the year because of the lack of autotrophic production and sporadic allochthonous input. Due to the temporal and spatial patchiness of food availability in most groundwater biotopes, periods of prolonged starvation are common events in the life of subterranean (i.e. hypogean) organisms (Poulson, 1964; Hüppop, 1985, 1986; Hervant et al., 1997). The ability to withstand and recover from long periods of nutritional stress is a critical adaptation for survival of any organism in food- limited systems. Therefore, several hypogean species are thought to have evolved behavioral, physiological and/or metabolic adaptations that allow them to exploit harsh subterranean environments successfully. However, needs and life styles differ considerably between hypogean species (Danielopol and Rouch, 1991) and so their adaptations to food limitation might also differ. Although instantaneous ecological consequences of poor nutrition are sometimes hard to distinguish, the reproductive potential of animals may become reduced and the effects will be manifested at the population level through a smaller amount of offspring or reduced survival capacity of the young. The subterranean aquatic crustaceans Niphargus rhenorhodanensis and N. virei can survive without feeding for periods well in excess of 1 year (Gibert and Mathieu, 1980; Mathieu and Giber, 1980). In a previous paper (Hervant et al., 1997), it was pointed out that both hypogean amphipod species and the hypogean isopod Stenasellus virei are better adapted to lack of food than surface-related species and all crustaceans previously studied, with survival times exceeding 200 days. During long-term starvation, the locomotory, ventilatory and metabolic rates were drastically lowered in subterranean 3587 The Journal of Experimental Biology 202, 3587–3595 (1999) Printed in Great Britain © The Company of Biologists Limited 1999 JEB2182 The effects of long-term starvation and subsequent refeeding on intermediary and energy metabolism were investigated in two subterranean aquatic crustaceans, Niphargus rhenorhodanensis and Niphargus virei, and in a morphologically similar surface-dwelling species, Gammarus fossarum. The metabolic response to prolonged food deprivation was monophasic in G. fossarum, showing an immediate, linear and large decline in all of the energy reserves. In contrast, both subterranean organisms displayed successive periods of glucidic, proteo-glucidic then lipidic-dominant catabolism during food deprivation. In both subterranean species, lipids (51 % of the energy consumed during a 180-day starvation period) and proteins (44 %) were the most metabolized substrates in terms of total energy, whereas glycogen (5 %) contributed little energy. G. fossarum displayed a different energetic strategy: proteins comprised 56 % of the energy losses during a 28-day starvation period, total lipids some 39 % and glycogen reserves only 5 %. We propose an energy strategy for food-limited subterranean crustaceans involving the possession of (1) higher amounts of stored arginine phosphate, triglycerides and glycogen and (2) lower utilization rates of stored metabolites than G. fossarum and numerous other surface-dwelling crustaceans, making the fueling of food deprivation possible for a longer time. In addition, these species had a faster and more efficient assimilation of available nutrients during recovery from food deprivation, enabling preparation for a new nutritional stress. These specific adaptive responses might be considered, for N. virei and N. rhenorhodanensis, as an efficient energy-saving strategy for an environment where extended starvation periods alternate with sporadic feeding events, therefore improving their competitive advantages. Key words: intermediary metabolism, energy metabolism, starvation, catabolism, refeeding, amphipod, Niphargus rhenorhodanensis, Niphargus virei, Gammarus fossarum. Summary Introduction COMPARATIVE STUDY ON THE METABOLIC RESPONSES OF SUBTERRANEAN AND SURFACE-DWELLING AMPHIPODS TO LONG-TERM STARVATION AND SUBSEQUENT REFEEDING FRÉDÉRIC HERVANT 1, *, JACQUES MATHIEU 1 AND HERVÉ BARRÉ 2 1 Hydrobiologie et Ecologie Souterraines (ESA CNRS 5023) and 2 Physiologie des Régulations Energétiques, Cellulaires et Moléculaires (UMR CNRS 5578), Université Claude Bernard-Lyon I, F-69622 Villeurbanne Cedex, France *e-mail: hervant@cismsun.univ-lyon1.fr Accepted 27 September; published on WWW 29 November 1999