Metabolic acclimation to captivity in highveld mole-rats ( <i>Cryptomys hottentotus pretoriae</i> ) is driven by sex-specific body mass increases

Captivity represents a profound environmental shift that can induce physiological acclimation, yet its effects on metabolic rate remain poorly resolved, particularly in subterranean mammals. African mole-rats (Bathyergidae) are frequently studied under captive conditions, despite wide variation in acclimation periods prior to metabolic assessment. Here, we tested whether prolonged captivity alters resting metabolic rate (RMR) and related physiological traits in the highveld mole-rat Cryptomys hottentotus pretoriae, and whether such changes are associated with body mass and sex. Using open-flow respirometry, we measured RMR, mass-specific RMR (msRMR) and respiratory quotient (RQ) in the same population of wild-caught animals assessed 7 days post-capture (wild) and again after 12 months in captivity (captive). Whole-animal RMR did not differ between wild and captive groups, nor between sexes. However, msRMR was 26.1% lower following captivity, coincident with a 28.1% increase in mean body mass. This mass gain was strongly sex-specific: males increased body mass by 52.4%, whereas females showed no significant change. Despite this, sex did not independently explain variation in RMR or msRMR. Captive animals also exhibited lower RQ values than recently captured individuals, suggesting shifts in substrate utilisation or energetic state. Together, these results indicate that apparent reductions in msRMR following captivity are driven primarily by increases in metabolically inactive tissue rather than suppression of whole-animal metabolic rate. Our findings highlight the importance of accounting for captivity-induced changes in body mass and composition when interpreting metabolic data, and caution against direct comparisons between unacclimated and long-term captive animals.