Evidence for physiological niche expansion of an intertidal flatworm: evolutionary rescue in the wild

<jats:p>Microevolution may enable populations to adapt physiologically to rapid climate change. Where it exists, historical data could provide a rare opportunity to document such adaptation. The intertidal flatworm <jats:italic>Procerodes littoralis</jats:italic> experiences large changes in salinity throughout the tidal cycle. We investigated whether regeneration performance of <jats:italic>P. littoralis</jats:italic> has changed over the last century. We repeated identical experiments to those published in 1914 on the same species and from the same location. In the modern experiment, when tested across a range of different salinities (S = 3, 6, 28, 44 and 53), <jats:italic>P. littoralis</jats:italic> could regenerate at lower salinities (S = 3) than reported previously. Also in the modern study, no significant optimum salinity could be identified, whereas in 1914 the optimum salinity (S = 28.5) was clear. The possibility of differences resulting from acclimation or oxygen availability instead of adaptation was investigated and discounted. It would appear that individuals from this population have extended their tolerance performance range further into hyposaline waters in the intervening 104 yr since the previous study. Local climate change is suggested to be the microevolution driver, as mean daily precipitation has increased and the number of days per year with no/trace precipitation has decreased in Plymouth, UK. Climate change is often considered a global phenomenon, but it drives local regime shifts. Here, we suggest an evolutionary shift attributable to a century-long local change in precipitation.</jats:p>