Population differences in early life‐history traits in grayling

In this paper we test population differences in early life‐history traits in three grayling Thymallus thymallus populations. The grayling shared ancestors some 80–90 years ago. We performed common‐garden experiments at three temperatures (mimicking population‐specific summer temperatures), and measured survival and growth rates during early development. We found significant additive genetic variance in size (length and yolk‐sac volume) measured at hatching, swim‐up and termination of the experiment, and significantly different reaction norms for growth rate and survival during the period of first feeding. In general, each population did best at the temperature experienced in nature. These differences in early life‐history traits suggest that natural selection has resulted in local adaptation in a time period of 13–18 generations.