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

Authors: GALLEGO-TÉVAR, BLANCA - University Of Sevilla; Grewell, Brenda; VALLET, DOMINIQUE - University Of Rennes, France; ROUSSEAU, HELENE - University Of Rennes, France; KELLER, JEAN - University Of Rennes, France; LIMA, OSCAR - University Of Rennes, France; DREANO, STEPHANE - University Of Rennes, France; SALMON, ARMEL - University Of Rennes, France; FIGUEROA, ENRIQUE - University Of Rennes, France; AINOUCHE, MALIKA - University Of Rennes, France; CASTILLO, JESUS - University Of Sevilla

Submitted to: Perspectives in Plant Ecology, Evolution and Systematics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2019
Publication Date: 2/28/2019
Citation: Gallego-Tévar, B., Grewell, B.J., Vallet, D., Rousseau, H., Keller, J., Lima, O., Dreano, S., Salmon, A., Figueroa, E., Ainouche, M., Castillo, J. 2019. Genetic structure of Spartina hybrids between native Spartina maritima and invasive Spartina densiflora in southwest Europe. Perspectives in Plant Ecology, Evolution and Systematics. 37:26-38. https://doi.org/10.1016/j.ppees.2019.02.001.
DOI: https://doi.org/10.1016/j.ppees.2019.02.001

Interpretive Summary: Interspecific plant hybridization represents an evolutionary force that promotes rapid genetic, epigenetic and phenotypic changes. To identify the role of hybrids in the structuring of plant communities, it is necessary to analyze their underlying population genetics, dispersion mechanisms, and the intensity of selection. In hybrids including at least one invasive species crossed with a native or non-native species, it has been reported that heterosis frequently increases the invasiveness of the offspring such as the hybrids between native Spartina foliosa Trin. and invasive S. alterniflora Loisel in San Francisco Bay. Hybridization involving an invasive species also often counteracts the decrease in population genetic variability as a consequence of bottlenecks in punctual invasions, increasing the success of the invasion in the offspring. In the genus of polyploid grasses Spartina (Poaceae), there are several examples of hybrids and allopolyploids between invasive and native species with transgressive traits that confer hybrid vigor. We studied the genetic structure of populations of hybrids between the native S. maritima and invasive S. densiflora in relation to their parental species. We analyzed the relationship of genetic distances among populations with (1) their geographic distance to assess the relative contribution of gene flow and drift in the population structure and consequent isolation by distance, (2) their abiotic environmental distances to identify the influence of processes of local adaptation and isolation by environment, and (3) their phenotypic differentiation by using morphological markers to evaluate the relationship between genetic and phenotypic distances. Our results indicate populations of sterile exotic Spartina hybrids between the native S. maritima and the invasive S. densiflora in the Southwest Iberian Peninsula are establishing hybrid zones with a spatial genetic structure inherited from both parental species. The hybrid populations with greater genetic differentiation are those more spatially separated from each other and that are present in more contrasted sedimentary environments, revealing respective isolation processes by distance and by environment. This study provides new data on the dynamics of exotic hybrid invasions, integrating effects of the genetic, phenotypic, geographical and environmental scenario with hybridization following invasion of a halophyte community by an exotic plant species. This contributes to improved understanding of the genetic mechanisms underlying the impacts of invasive hybrid plant taxa on native plant communities.

Technical Abstract: Interspecific plant hybridization represents an evolutionary force that promotes rapid genetic, epigenetic and phenotypic changes. To identify the role of hybrids in the structuring of plant communities, it is necessary to analyze their underlying population genetics, dispersion mechanisms, and the intensity of selection. In hybrids including at least one invasive species crossed with a native or non-native species, it has been reported that heterosis frequently increases the invasiveness of the offspring such as the hybrids between native Spartina foliosa Trin. and invasive S. alterniflora Loisel in San Francisco Bay. Hybridization involving an invasive species also often counteracts the decrease in population genetic variability as a consequence of bottlenecks in punctual invasions, increasing the success of the invasion in the offspring. In the genus of polyploid grasses Spartina (Poaceae), there are several examples of hybrids and allopolyploids between invasive and native species with transgressive traits that confer hybrid vigor. We studied the genetic structure of populations of hybrids between the native S. maritima and invasive S. densiflora in relation to their parental species. We analyzed the relationship of genetic distances among populations with (1) their geographic distance to assess the relative contribution of gene flow and drift in the population structure and consequent isolation by distance, (2) their abiotic environmental distances to identify the influence of processes of local adaptation and isolation by environment, and (3) their phenotypic differentiation by using morphological markers to evaluate the relationship between genetic and phenotypic distances. Our results indicate populations of sterile exotic Spartina hybrids between the native S. maritima and the invasive S. densiflora in the Southwest Iberian Peninsula are establishing hybrid zones with a spatial genetic structure inherited from both parental species. The hybrid populations with greater genetic differentiation are those more spatially separated from each other and that are present in more contrasted sedimentary environments, revealing respective isolation processes by distance and by environment. This study provides new data on the dynamics of exotic hybrid invasions, integrating effects of the genetic, phenotypic, geographical and environmental scenario with hybridization following invasion of a halophyte community by an exotic plant species. This contributes to improved understanding of the genetic mechanisms underlying the impacts of invasive hybrid plant taxa on native plant communities.