Seasonal variation in faecal glucocorticoid metabolite concentrations of two dominant southern African murids (Lemniscomys rosalia and Mastomys coucha) across variously transformed landscapes

Global landscape transformations are a result of a growing human population and the subsequent increased use of natural habitats. Local species extinctions across various transformed landscapes emphasise the importance of monitoring wildlife responses to anthropogenic activities. Rodents are valuable biological indicators of anthropogenic disturbance and, subsequently, ecosystem health. The study quantified faecal glucocorticoid metabolites (fGCMs) as a stress-related biomarker in two dominant southern African murids, Lemniscomys rosalia (single-striped grass mouse) and Mastomys coucha (southern multimammate mouse), across dry and wet seasons within minimally and moderately disturbed landscapes in the Magaliesberg Biosphere, South Africa. Faecal samples were collected from live-trapped individuals, and fGCMs were quantified using a previously validated 5α-pregnane-3β,11β,21-triol-20-one enzyme immunoassay (detecting fGCMs with a 5α-3β, 11β-diol structure). Mastomys coucha showed a significant increase in fGCM concentrations during the wet season (58% and 22% higher in the minimally and moderately transformed sites, respectively). For L. rosalia, fGCM concentrations were not significantly different between seasons. Landscape-specific fGCM concentrations did not differ significantly in either species, reflecting the generalist, synanthropic nature of both species. While these species are morphologically and ecologically similar, their seasonal fGCM profiles diverged significantly in natural landscapes. The 58% increase in median fGCM concentrations for M. coucha was not seen in L. rosalia. This physiological differentiation between species may perhaps be elucidated by the energetic and behavioural strategies they employ to cope with seasonal resource fluctuations in natural habitats. Despite their phenotypic plasticity and behavioural adaptability, dominant generalist species such as M. coucha are affected by seasonal shifts. Greater climatic fluctuations across seasons should be investigated as they may lead to chronic stress-related hormone responses, and, in extreme cases, reduced survival and local extinctions.