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 a wide thermal range.
• Environmental variation often co-occurs with other selection pressures, potentially limiting adaptation to temperature.
• Understanding these interactions is crucial for predicting evolutionary responses to climate change.

Purpose of the Study:

• To investigate the evolutionary outcomes of bacteriophages under fluctuating temperatures and competition.
• To determine how thermal specialists and generalists respond to combined environmental stressors.
• To assess the impact of fluctuating temperatures and co-selection on adaptive evolution.

Main Methods:

• Propagation of two competing bacteriophages (thermal specialist φ14-1 and thermal generalist φLUZ19) infecting *Pseudomonas aeruginosa*.
• Experimental conditions included fluctuating temperatures (37°C-42°C) in monoculture and co-culture.
• Analysis of evolutionary trajectories, genetic distance, and adaptive mutations.

Main Results:

• Fluctuating temperatures promoted intermediate thermal phenotypes in the specialist 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.
• Co-selection restricted thermal adaptation, reduced genetic divergence from the ancestor, and lowered the number of adaptive mutations in the generalist phage φLUZ19.

Conclusions:

• Variable adaptive capacity exists within interacting microbial communities facing fluctuating environments.
• The interplay between thermal variation and competition significantly influences evolutionary trajectories.
• These findings have implications for understanding community responses to global climate change.