Maternal effects alter natural selection on phytochromes through seed germination

1. Phytochromes regulate seed germination in response to light and temperature, and different phytochromes contribute to germination under different environmental conditions. 2. Using Arabidopsis thaliana mutants with different combinations of non-functional phytochromes, we tested which phytochromes contribute to germination and other life-history traits under field conditions and whether that contribution changes with seed-maturation temperature. We also quantified natural selection on phytochrome variants through their influence on seed germination. 3. We found that some phytochromes contributed to germination under field conditions and that the phytochrome that contributed most strongly depended on seed-maturation temperature. Specifically, when seeds were matured under warm temperature, phyA and phyE null plants had the most strongly reduced germination, with phyA not able to germinate late in the season. In contrast, when seeds were matured under cool temperature, phyB nulls had the most reduced germination, and effects of the phyA mutation were apparent only on a phyB background. 4. These effects on germination translated to effects on total lifetime fitness, such that selection on phytochromes that contributed to germination sometimes depended on seed-maturation conditions. 5. Synthesis. Natural selection on phytochromes occurs through their effects on seed germination, and maternal effects alter phytochrome contributions to germination. Therefore, maternal effects can alter natural selection on phytochromes. The results demonstrate a novel role of maternal effects in contributing to variable natural selection on specific genes associated with plant responses to climatic conditions.