Fitness of reciprocal F1 hybrids between Rhinanthus minor and Rhinanthus major under controlled conditions and in the field

The performance of first‐generation hybrids determines to a large extent the long‐term outcome of hybridization in natural populations. F1 hybrids can facilitate further gene flow between the two parental species, especially in animal‐pollinated flowering plants. We studied the performance of reciprocal F1 hybrids between Rhinanthus minor and R. major, two hemiparasitic, annual, self‐compatible plant species, from seed germination to seed production under controlled conditions and in the field. We sowed seeds with known ancestry outdoors before winter and followed the complete life cycle until plant death in July the following season. Germination under laboratory conditions was much lower for the F1 hybrid formed on R. major compared to the reciprocal hybrid formed on R. minor, and this confirmed previous results from similar experiments. However, this difference was not found under field conditions, which seems to indicate that the experimental conditions used for germination in the la...