Emerging gene-based diagnostics explain the relationship between wildlife health and habitat condition

We investigated how Mojave desert tortoises (Gopherus agassizii) respond to a variety of environmental conditions and ecological stressors using gene-based health diagnostics. Gene transcription measures an individual’s... [ view full abstract ]

We investigated how Mojave desert tortoises (Gopherus agassizii) respond to a variety of environmental conditions and ecological stressors using gene-based health diagnostics. Gene transcription measures an individual’s change in physiological status by quantifying the amount of messenger RNA (mRNA) that is transcribed for targeted genes in response to a variety of intrinsic and extrinsic ecological stressors. It improves the assessment of the condition in an organism by detecting the earliest observable signs of changes in health at the cellular level. We developed a qPCR assay for the desert tortoise, targeting genes that regulate immune function, responses to bacterial and viral pathogens, inflammation, nutritional stress, toxicants, metabolism, and other cellular conditions. Through a controlled experiment, we found that native plant diets frequently intermixed or replaced by non-native grasses negatively influence the physiological ecology, immune-competence, health, and survival of young tortoises. Tortoises eating native forage (annual forbs and grasses) had better body condition and immune functions, grew more, and had higher survival rates (>95%) than tortoises consuming non-native grass diets. Health and body condition quickly declined for tortoises foraging only on the invasive grass Bromus rubens, with notable loss of fat and muscle mass, and increased muscular atrophy. B. rubens seeds were found embedded in the oral mucosa and tongue in most individuals eating that diet, with subsequent inflammation. Genes indicative of physiological, immune, and metabolic functions were transcribed at lower levels for individuals foraging on B. rubens, indicating potential greater susceptibility to disease or other health related problems. At the end of the experiment, 32% of individuals fed only native grass and 37% fed invasive grass were found dead or removed from the experiment due to poor body conditions. In contrast, tortoises fed the native forb diet had zero mortality, grew substantially, and were in good condition.