Metabolic responses to long-term food deprivation in subterranean and surface amphipods

Abstract

A long-standing hypothesis in subterranean biology posits that organisms living in poor resource subsurface habitats can withstand long periods of bioenergetic shortages due to an innate reduced metabolic rate when compared to their epigean counterparts. However, previous studies have proposed that caves with ample energy resources may not evolve organisms with reduced metabolic rate. The equivocal nature of previous findings suggests that there is a need to compare food deprivation responses of subterranean and surface species in order to elucidate whether there are widespread adaptations to low energy systems in subterranean taxa. The purpose of the study was to examine patterns in basal metabolism and the effects of food deprivation in closely related subterranean- and epigean- amphipods, Stygobromus pecki and Synurella sp. from central and east Texas, USA, respectively. Basal metabolic rates (measured as O2 consumption) differed between species, with S. pecki having substantially lower rates than Synurella. Individuals of both species were food deprived for a pre-determined time interval and changes in total body protein, lipids, and carbohydrates were measured throughout food deprivation experiments. Stygobromus pecki had larger initial energy stores than Synurella and were more conservative in the use of energetic reserves over a prolonged period of food deprivation. Thus, it appears that although S. pecki are currently found in shallow phreatic and spring opening environments, they have maintained more efficient metabolic adaptations to deal with prolonged periods of food deprivation.