Breathing in the dark interactive influence of intrinsic and extrinsic factors on stygofauna metabolic rate

Metabolic rate is a key physiological trait shaping ecological and evolutionary processes, yet research on subterranean organisms remains scarce. With climate change increasingly impacting groundwater ecosystems, understanding how stygofauna respond to abiotic stressors is vital. We investigated the standard metabolic rate (SMR) of Spelaeomysis bottazzii Caroli, 1924, an endemic groundwater crustacean, under varying temperature and salinity conditions. Using constant volume respirometry, we measured oxygen consumption in 54 individuals across three temperatures (17, 21, and 25°C) and salinities (2, 4, and 6). We also assessed the effects of body mass, sex, and potential Consistent Individual Differences (CIDs) in SMR. S. bottazzii exhibited a notably low SMR compared to epigean related crustaceans, supporting the hypothesis of metabolic suppression in resource-limited environments. SMR scaled with temperature (E = 0.85 eV) and body mass (b = 0.44), though with lower explanatory power than in epigean species. Salinity, sex, and mass-temperature interactions had no significant effect, and no CIDs were detected. Long-term observations revealed slow growth, low mortality, and extended lifespan, indicating a slow-paced life history. These findings enhance our understanding of subterranean metabolic scaling and underscore the importance of studying stygofauna resilience under environmental change.