Environmental temperature and immune activation during development: effects on organ growth in juvenile degus

In this study, we investigated the influence of environmental temperature and immune challenge on organ and body mass in juvenile degus (Octodon degus). Using an experimental design with two temperature treatments (15 °C and 30 °C) and a lipopolysaccharide (LPS)-induced immune challenge, we measured the mass of key organs (kidney, heart, liver, spleen, lung) as well as body mass. Our results showed that temperature alone significantly affected kidney, heart, lung, and body mass, with individuals reared at 30 °C exhibiting larger organs and greater body mass, consistent with thermoneutral conditions. Immune challenge with LPS primarily affected lung mass, with challenged individuals showing larger lungs regardless of temperature. However, no significant changes were observed in spleen or liver mass, and no interactions between temperature and immune challenge were detected. These findings suggest that temperature-driven developmental plasticity plays a dominant role in shaping organ and body traits, while immune activation induces organ-specific responses. Our results highlight the importance of environmental temperature in shaping physiological traits and raise questions about the long-term effects of immune challenges and temperature interactions on wildlife health and fitness.