Phenotypic plasticity of polyploid plant species promotes transgressive behaviour in their hybrids.

Hybridization is a frequent process that leads to relevant evolutionary consequences, but there is a lack of studies regarding the relationships of the variability of the response of parental plant species to environmental gradients and the responses of their hybrids at a phenotypic level. We designed an experiment in which we exposed two reciprocal cordgrass hybrids, Spartina maritima × densiflora and S. densiflora × maritima, and their parental species to four salinity concentrations for 30 days. The main objectives were to compare the performance of the hybrids with that of their parents, to distinguish the phenotypic inheritance operating in the hybrids and to analyse the relationships between the variability in the responses of the parents and the responses of their hybrids to salinity. We characterized the responses and the degree of variability for 37 foliar traits. Both hybrids presented greater salinity tolerance than their parents, showing their highest percentage of transgressive traits at both extremes of the salinity gradient. When the parental plants themselves showed a more plastic response for a given trait, there was a greater chance that their hybrid developed a transgressive behaviour for this trait. This finding supports a new focus to be applied for the artificial development of vigorous hybrid crops.