Vertebrate endothermy restricts most fungi as potential pathogens

Area of Science:

• Mycology
• Infectious Diseases
• Evolutionary Biology

Background:

• Fungal infections pose a significant threat to plants, amphibians, and insects, yet mammals exhibit remarkable resistance.
• The underlying reasons for this disparity in susceptibility to fungal pathogens remain largely unexplained.

Purpose of the Study:

• To investigate the thermal tolerance of a wide range of fungal species.
• To determine the correlation between fungal growth temperature limits and mammalian body temperatures.
• To explore the role of endothermy and homeothermy in mammalian antifungal defense.

Main Methods:

• Analysis of thermal tolerance data for 4802 fungal strains across 144 genera.
• Comparison of thermal tolerance between fungi isolated from various environments (insects, mammals, soil, plants).
• Modeling the impact of temperature increases on fungal growth exclusion.

Main Results:

• The majority of fungal strains tested demonstrated an inability to grow at typical mammalian core body temperatures (around 37°C).
• Fungi originating from insect and mammalian hosts exhibited higher thermal tolerances compared to soil and plant-associated fungi.
• A 1°C increase in temperature within the 30°C–40°C range led to a 6% increase in fungal isolate exclusion.

Conclusions:

• Mammalian endothermy (internal heat generation) and homeothermy (stable internal temperature) serve as crucial, non-specific defenses against a broad spectrum of fungal pathogens.
• Elevated body temperatures, such as those during fever, can significantly expand this thermal exclusion zone, further protecting mammals from fungal infections.
• These thermoregulatory mechanisms likely conferred a substantial evolutionary advantage, contributing to the lower incidence of fungal diseases in mammals.