Effects of ambient temperatures on evolutionary potential of reproductive timing in boreal passerines

1. Many populations need to adapt to changing environmental conditions, such as warming climate. Changing conditions generate directional selection for traits critical for fitness. For evolutionary responses to occur, these traits need to be heritable. However, changes in environmental conditions can alter the amount of heritable variation a population expresses, making predictions about expected responses difficult.

2. The aim of this study was to evaluate the effects of ambient temperatures on evolutionary potential and strength of natural selection on the timing of reproduction in two passerine birds breeding in boreal forests.

3. Long-term data on individually marked Willow Tits (Poecile montanus, 1975–2018) and Great Tits (Parus major, 1969–2018) were analysed with random regression animal models to assess if spring temperatures affect the expressed amount of additive genetic variation (VA) and heritability (h2) in the timing of breeding. We assessed if ambient temperatures...