Transgressivity in Key Functional Traits Rather Than Phenotypic Plasticity Promotes Stress Tolerance in A Hybrid Cordgrass

Abstract

Hybridization might promote offspring fitness via a greater tolerance to environmental stressors due to heterosis and higher levels of phenotypic plasticity. Thus, analyzing the phenotypic expression of hybrids provides an opportunity to elucidate further plant responses to environmental stress. In the case of coastal salt marshes, sea level rise subjects hybrids, and their parents, to longer tidal submergence and higher salinity. We analyzed the phenotypic expression patterns in the hybrid Spartina densiflora x foliosa relative to its parental species, native S. foliosa, and invasive S. densiflora, from the San Francisco Estuary when exposed to contrasting salinities and inundations in a mesocosm experiment. 37% of the recorded traits displayed no variability among parents and hybrids, 3% showed an additive inheritance, 37% showed mid-parent heterosis, 18% showed best-parent heterosis, and 5% presented worst-parent heterosis. Transgressivity, rather than phenotypic plasticity, in key functional traits of the hybrid, such as tiller height, conveyed greater stress tolerance to the hybrid when compared to the tolerance of its parents. As parental trait variability increased, phenotypic transgressivity of the hybrid increased and it was more important in response to inundation than salinity. Increases in salinity and inundation associated with sea level rise will amplify the superiority of the hybrid over its parental species. These results provide evidence of transgressive traits as an underlying source of adaptive variation that can facilitate plant invasions. The adaptive evolutionary process of hybridization is thought to support an increased invasiveness of plant species and their rapid evolution.

Adaptation of the Invasive Plant Sphagneticola trilobata to Flooding Stress by Hybridization with Native Relatives

“…Several authors have reported that hybridization during plant invasion may produce more adaptable hybrid species [ 4 , 5 , 36 ]. For example, the hybridization between the native species Spartina foliosa and the invasive species S. densiflora enhanced the adaptability of the hybrid species to salt and flooding stress [ 7 ]. In our previous research, the tolerance of Sphagneticola × guangdongensis to cadmium and drought stress was inconsistent with the tolerance of Sphagneticola × guangdongensis to flooding stress in this study [ 32 , 33 , 34 , 35 ].…”

“…petiolaris [ 6 ]. Hybridization is particularly important under constantly changing environmental conditions [ 7 ]. Heterosis is the result of the non-additive phenotypic expression of one or more traits, which may be regulated by epigenetics and genetics.…”