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, a groundwater crustacean endemic of Apulia (SE Italy), 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) on 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 and tolerance to moderate variations in habitat conditions. In contrast to the common assumption of strict niche specialization in subterranean fauna, our findings on S. bottazzii reveal a comparatively broad tolerance to temperature and salinity. This trait is particularly relevant in the context of ongoing climate change, as it suggests a higher resilience of this species than previously expected.