Data for: Reconsidering the evolutionary speed hypothesis: Adaptive pathway matters

Warmer is believed to accelerate evolution by physiological and ecological mechanisms. However, this framework overlooked the constraining role of adaptive pathway. Here we tested the hypothesis that a shift to the cold reshapes the adaptive landscape and accelerates evolution even warmer temperature enhances evolutionary drivers using a model bacterium. Two clones were isolated from the populations that pre-adapted to 26℃ and evolved at 12, 19 and 26℃. Populations evolving at colder temperatures showed higher fitness increase although the warmer increased population sizes, growth rates and mutation rates. This is likely caused by the position of pre-adapted clones, near local fitness peaks, and a shift to colder environments repositioned these trapped clones onto ascending slopes of the adaptive landscape, resulting in faster adaptation. We also found that environmental shift may help population cross fitness valleys. Our findings highlight the temperature-dependent evolutionary speed relies on the accessibility of adaptation pathways.