Seasonal coupling between stress physiology and gastrointestinal nematode communities in wild and semi-captive populations of an endangered ungulate

Integrating endocrine stress biomarkers with parasite community dynamics can help clarify how environmental and management-related pressures relate to host-parasite interactions in endangered wildlife. However, relationships between physiological stress and parasite dynamics remain poorly understood, particularly in high-altitude ecosystems. Here, we investigated the endangered Przewalski's gazelle (Procapra przewalskii), endemic to the Qinghai-Tibet Plateau, by combining faecal cortisol quantification with amplicon sequencing of the internal transcribed spacer 2 region of ribosomal DNA from gastrointestinal nematodes. Seasonal patterns in physiological stress and nematode community composition were compared between wild and semi-captive populations. Both faecal cortisol concentrations and nematode community composition showed pronounced seasonal variation. Trichostrongylidae reached its highest relative read abundance in summer, whereas Molineidae reached its highest relative read abundance in spring. During spring, semi-captive gazelles exhibited higher faecal cortisol concentrations and greater relative representation of Trichostrongylidae than wild gazelles. Across samples, Trichostrongylidae and Molineidae showed nearly perfectly complementary relative read abundances. Generalized linear models with a Gamma error distribution showed significant associations between faecal cortisol concentrations and the relative read abundance of each dominant nematode family after accounting for season and population type, whereas relative read abundance × population type interactions were not statistically supported. These findings reveal pronounced seasonal associations between endocrine stress responses and gastrointestinal nematode dynamics in Przewalski's gazelle, while providing no evidence that the parasite-cortisol association differed between wild and semi-captive populations. Our study advances the integration of stress endocrinology and disease ecology in conservation physiology and supports the value of combining non-invasive endocrine and parasitological biomarkers in wildlife health assessment.