From genomes to phenomes: Do deleterious mutations correlate with cellular performance in white rhinos?

The distribution, frequency, and severity of genetic load (the accumulation of deleterious alleles, levels of homozygosity, and heterozygosity) are widely used as metrics for fitness and viability in small populations. Higher allelic diversity may enable populations to persist and evolve in unpredictable environments, suggesting that individuals with higher homozygosity, lower heterozygosity, and higher inbreeding coefficients may exhibit reduced fitness. Under a climate change scenario, drastic temperature fluctuations might be particularly challenging to thrive and survive due to their deleterious physiological effects. Our goal is to test whether performance of primary fibroblasts under heat stress correlates with genetic load parameters in the threatened Southern White Rhino ( Ceratotherium simum simum ). Published data on homozygosity, heterozygosity, and inbreeding scores will be correlated with cellular and mitochondrial function, assessed through multiple physiological markers. To obtain this data, primary fibroblasts (n = 15) were exposed to either 41°C (heat stress) or 37°C (control) for 24 hours. Afterwards, mitochondrial function was measured via a mitochondrial stress test (Agilent Seahorse Analyzer), cellular morphology (nuclear size and cytoskeletal organization, mitochondrial distribution) was evaluated through immunofluorescence (IF) staining, along with senescence markers (β-galactosidase presence), oxidative stress (reactive oxygen species presence), and RNA transcription (SYTO RNA Select stain). Heat shock protein (HSP70) abundance will be quantified using western blot analysis. The IF data were analyzed with CellProfiler™ software or with IF spectrophotometer. Preliminary results show that acute exposure to heat result in a series deleterious effects on SWR fibroblasts performance, including significant reduction of mitochondrial function (basal respiration: t = 3.7, df = 9, p < 0.01; maximum respiration: t = 3.0, df = 9, p < 0.02; ATP production: t = 5.8, df = 9, p < 0.001; coupling efficiency: t = 7.6, df = 9, p < 0.001) and ROS production (t = 3.35, df = 7, p = 0.01). Heat stress also increases nuclear size (area: t = 6.8, df = 9, p < 0.001) without altering RNA transcription (p = 0.63), and increase the presence of the senescence marker (W = 104.0, n = 15, p < 0.001). Future analyses will test the if genetic load parameters can explain individual cellular thermosensitivity. This study aims to provide insights into the connection between genetic markers and organismal performance under global warming scenario, as cellular and mitochondrial function plays a fundamental role in an organism's ability to adjust and thrive under environmental change. San Diego Zoo Wildlife Alliance This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.