Climate-Driven Fungal Thermotolerance

Fungal thermotolerance is the capacity of a fungus to survive or grow at relatively high temperatures. Climate warming can favour fungi carrying heritable heat-tolerance traits, causing those traits to become more common over generations. This is an evolutionary population response, not a purposeful adjustment by individual organisms.

Evolutionary selection process

Fungal populations normally contain variation produced by mutation, recombination and gene flow. When temperatures repeatedly approach their upper tolerance limits, heat becomes a selection pressure rather than merely a temporary disturbance.

• Heat-tolerant individuals are more likely to survive, reproduce and transmit tolerance-associated variants.
• Repeated differential reproduction increases the frequency of advantageous variants through natural selection.
• Selection may act on existing genetic variation, so adaptation need not await a new mutation.
• Migration can introduce tolerant variants into new populations, while local conditions determine whether they persist.

Biological basis of tolerance

Selected changes may improve protein stability, cellular repair, membrane functioning or the regulation of stress-response pathways. Heat-shock proteins help protect or refold proteins damaged by elevated temperature, while changes in membrane lipids can preserve membrane function.

• Short-term physiological adjustment is acclimation; evolutionary thermotolerance requires heritable change across generations.
• Tolerance is most likely to evolve where high-temperature exposure is recurrent and affects reproductive success.

Consequences and limits

Warming may shift a population's thermal range upward and allow it to occupy previously unsuitable habitats. Because mammalian body temperature excludes many environmental fungi, greater thermotolerance could reduce one barrier to infection.

• Thermotolerance alone does not make a fungus pathogenic; host entry, nutrient acquisition, immune evasion and tissue damage are separate requirements.
• Evolution is not inevitable: limited variation, weak selection, dispersal and fitness trade-offs can constrain adaptation.