Competition constrains parasite adaptation to thermal heterogeneity

Area of Science:

• Evolutionary biology
• Microbial ecology
• Climate change adaptation

Background:

• Temporal thermal heterogeneity is predicted to favor generalist phenotypes capable of growth across diverse temperatures.
• However, adaptation to thermal variation can be constrained by interacting selection pressures, such as competition.
• Understanding these interactions is crucial for predicting microbial evolution in a changing climate.

Purpose of the Study:

• To investigate the evolutionary responses of bacteriophages to fluctuating temperatures under monoculture and co-culture conditions.
• To determine how competition influences adaptation to thermal heterogeneity in viral communities.
• To assess the potential for variable adaptive capacity in interacting microbial populations facing climate change.

Main Methods:

• Propagation of two competing bacteriophages (thermal specialist φ14-1 and thermal generalist φLUZ19) infecting *Pseudomonas aeruginosa*.
• Experimental evolution under fluctuating temperatures (37°C-42°C) in both monoculture and co-culture settings.
• Analysis of evolutionary outcomes, including thermal phenotypes, genetic distance, and adaptive mutations.

Main Results:

• Fluctuating temperatures led to intermediate thermal phenotypes in phage φ14-1 and increased evolutionary variability in both phages compared to static conditions.
• Co-selection with fluctuating temperatures accelerated thermal adaptation in phage φ14-1.
• Conversely, co-selection restricted thermal adaptation, reduced genetic divergence, and lowered the number of adaptive mutations in phage φLUZ19.

Conclusions:

• Variable adaptive capacity exists within interacting microbial communities under fluctuating thermal conditions.
• Competition significantly modulates the evolutionary trajectory of viruses adapting to environmental change.
• These findings have implications for predicting the ecological and evolutionary consequences of global climate change on microbial communities.