Effect of fasting on hypogean (Niphargus stygius) and epigean (Gammarus fossarum) amphipods: a laboratory study

Two amphipods, the hypogean Niphargus stygius and epigean Gammarus fossarum, were analyzed for fatty acid (FA) composition, electron transport system (ETS) activity and respiration (R) during a laboratory fasting experiment. In agreement with ETS and R measurements (and the ETS/R ratio), the hypogean N. stygius utilized FA more slowly than the epigean G. fossarum. Inter-specific differences in the utilization of certain FA during fasting were also revealed. While N. stygius tended to preserve all of its FA during the experimental fasting period, G. fossarum showed a tendency to utilize MUFA (monounsaturated FA) and SAFA (saturated FA) and preferentially retain PUFA (polyunsaturated FA). The significant correlations between ETS activity and composition of specific FA during fasting can be linked to R. During the fasting, both ETS activity and respiration rate of G. fossarum decreased, however, ETS/R ratio increased. In contrast, N. stygius did not show significant changes in these parameters. This is the first report, which connects ETS activity with changes in concentrations of specific FA during fasting. Such evolutionary adaptations of hypogean species enables them to better survive chronically low and/or discontinuous food supplies compared to epigean species, which live in environments where food shortages are much less frequent.