Low genetic diversity contrasts with high phenotypic variability in heptaploid Spartina densiflora populations invading the Pacific Coast of North America

Authors: CASTILLO, JESUS - University Of Sevilla; GALLEGO-TEVAR, BLANCA - University Of Sevilla; FIGUEROA, ENRIQUE - 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; AINOUCHE, MALIKA - University Of Rennes, France

Submitted to: Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2018
Publication Date: 4/20/2018
Citation: Castillo, J.M., Gallego-Tevar, B., Figueroa, E., Grewell, B.J., Vallet, D., Rousseau, H., Keller, J., Lima, O., Dreano, S., Salmon, A., Ainouche, M. 2018. Low genetic diversity contrasts with high phenotypic variability in heptaploid Spartina densiflora populations invading the Pacific Coast of North America. Ecology and Evolution. 8(10):4992-5007. https://doi.org/10.1002/ece3.4063.
DOI: https://doi.org/10.1002/ece3.4063

Interpretive Summary: Environmental and macroclimatic variation along latitudinal gradients provides a natural laboratory to evaluate the effects of changing environmental conditions on the biological responses, ecology and evolution of invasive plant species. Species can respond to environmental stresses in novel habitats through genetic and epigenetic changes and through phenotypic plasticity, but few studies have evaluated the relationships between genetic differentiation and phenotypic plasticity of plant species along changing environmental conditions such as throughout wide latitudinal ranges. We studied inter- and intra-population genetic diversity (using Simple Sequence Repeats and chloroplast DNA sequencing) and phenotypic plasticity of 33 plant traits (using field and common-garden measurements) for five populations of the invasive cordgrass Spartina densiflora Brongn. along the Pacific coast of North America from San Francisco Bay to Vancouver Island. Studied populations showed very low genetic diversity, high levels of phenotypic variability when growing in contrasted environments, and similar, fixed and high intra-population phenotypic variability for many plant traits. This intra-population phenotypic variability was especially high, irrespective of environmental conditions, for those traits showing also high phenotypic plasticity. Within-population variation represented 84% of the total genetic variation coinciding with certain individual plants keeping consistent responses for three plant traits (chlorophyll b and carotenoids contents, and dead shoot biomass) in the field and in common-garden conditions. In view of our results, multiple introductions are unknown but possible since, for example, the population from Vancouver Island was the most recent and one of the most genetically diverse. S. densiflora appears to be a species that would not be very affected itself by climate change and sea level rise since it can disperse, establish and acclimate to contrasted environments along wide latitudinal ranges. This study demonstrates how evolutionary factors can inform invasive species risk assessments, and contributes to risk assessment and management planning for invasive cordgrass at continental scales.

Technical Abstract: Species can respond to environmental pressures through genetic and epigenetic changes and through phenotypic plasticity, but few studies have evaluated the relationships between genetic differentiation and phenotypic plasticity of plant species along changing environmental conditions such as throughout wide latitudinal ranges. We studied inter- and intra-population genetic diversity (using Simple Sequence Repeats and chloroplast DNA sequencing) and phenotypic plasticity of 33 plant traits (using field and common-garden measurements) for five populations of the invasive cordgrass Spartina densiflora Brongn. along the Pacific coast of North America from San Francisco Bay to Vancouver Island. Studied populations showed very low genetic diversity, high levels of phenotypic variability when growing in contrasted environments, and similar, fixed and high intra-population phenotypic variability for many plant traits. This intra-population phenotypic variability was especially high, irrespective of environmental conditions, for those traits showing also high phenotypic plasticity. Within-population variation represented 84% of the total genetic variation coinciding with certain individual plants keeping consistent responses for three plant traits (chlorophyll b and carotenoids contents, and dead shoot biomass) in the field and in common-garden conditions. In view of our results, multiple introductions are unknown but possible since, for example, the population from Vancouver Island was the most recent and one of the most genetically diverse. S. densiflora appears to be a species that would not be very affected itself by climate change and sea level rise since it can disperse, establish and acclimate to contrasted environments along wide latitudinal ranges.