Differential metabolic response to temperature among populations of <i>Cyprideis torosa</i> (Jones, 1850) (Ostracoda: Cytherideidae)

Abstract Rising global temperatures reduce oxygen solubility in water bodies while increasing the metabolic demands of aquatic ectotherms. Oxygen consumption rate (OCR) varies widely across crustaceans and is influenced by developmental stage, sex, body mass, activity level, and environmental conditions such as temperature and salinity. We investigated how OCR responds to increasing temperatures in the podocopid ostracod Cyprideis torosa (Jones, 1850) by using optical sensor respirometry. Specifically, we compared adults and subadults from ostracod populations inhabiting distinct salinity regimes to assess how environmental history and life stage influence oxygen consumption. Results show that OCR increases with temperature across all populations, but the magnitude of this response differs markedly. Specimens from intermediate salinity (mesohaline) exhibited the highest OCR and strongest thermal response, whereas those from oligohaline and hyperhaline habitats showed lower OCR and reduced thermal flexibility. Subadults consistently consumed more oxygen than adults, particularly at higher temperatures. These findings highlight the role of local conditions, local adaptation, and ontogeny in shaping oxygen demand in C. torosa and provide new insights into its physiological response in the face of temperature and salinity variability.