Genetic structure of Spartina hybrids between native Spartina maritima and invasive Spartina densiflora in Southwest Europe

Abstract Interspecific hybridization represents an evolutionary force resulting in novel genotypes. The genomic changes that occur as a result of hybridization affect both genome structure and gene expression and consequently determine hybrid phenotypes and ecology. This study provides new data on the dynamics of hybrid invasions, integrating effects of the genetic, phenotypic, geographical and environmental scenarios with hybridization following invasion of a halophyte community by an exotic plant species. We analyzed the spatial genetic structure of sterile Spartina F1 hybrid populations established at the Gulf of Cadiz (Southwest Iberian Peninsula) and that of their parental species native S. maritima and invasive S. densiflora using nuclear DNA (Simple Sequence Repeats) and chloroplast DNA sequences. We also analyzed the relationships between the spatial genetic structure of the hybrids, their phenotypic variability and their marsh environment. The studied populations of Spartina hybrids were establishing hybrid zones with a spatial genetic structure inherited from both parental species. The hybrids were genetically more similar to the native than to the invasive species. The hybrid populations with greater genetic differentiation were those more spatially separated from each other and that were present in more contrasted sedimentary environments, revealing respective isolation processes by distance and by environment. The hybrids in the Guadiana Estuary were the most genetically differentiated and with the highest transgressive behavior in terms of tiller height.