Fig. 2

Water temperature in the wild and in the experimental setup in the lab. Left plot: Solid lines show the water temperatures in the natural spawning locations (measured every 30 min), and the dashed lines indicate when the two populations started spawning (i.e. when the experiment was started). Grey lines represent Harfjärden, and black lines represent Lervik. Right plot: Solid lines show the water temperatures in the three treatments in the experimental setup (black: high temperature treatment (12.3 °C), dark grey: medium temperature treatment (9.7 °C), and light grey: low temperature treatment (4.5 °C)). Horizontal dashed lines indicate the duration of the experiment for the two populations (grey line represents Harfjärden, and black line represents Lervik)