Gene flow favours local adaptation under habitat choice in ciliate microcosms.

Local adaptation is assumed to occur under limited gene flow. However, habitat-matching theory predicts dispersal should favour rather than hinder local adaptation when individuals selectively disperse towards habitats maximizing their performance. We provide experimental evidence that local adaptation to the upper margin of a species' thermal niche is favoured by dispersal with habitat choice, but hindered under random dispersal. Our study challenges the idea that high gene flow precludes local adaptation, and provides unique experimental evidence of habitat choice as an overlooked mechanism responsible for adaptation under rapid environmental changes.