Fine-scale spatial genetic structure across a strong environmental gradient in the saltmarsh plant Puccinellia maritima

Saltmarsh forms the transition between maritime and terrestrial environments where biotic and abiotic conditions vary substantially along a gradient in elevation. Theoretical and empirical population genetics studies have focused on the influence of environmental gradients on intra-specific genetic variation. Contrastingly, only a few studies have focused on genetic variation in saltmarsh plants, despite the potentially strong influence of environmental gradients shaping diversity in these species. In the present paper, we assess the genetic structure of the saltmarsh plant Puccinellia maritima collected across an elevation gradient in restored and natural saltmarsh. Both spatial autocorrelograms of genetic variation and spatial analysis of principal components detected genetic structurein the natural saltmarsh organized along the gradient in elevation, yet no such pattern was identified considering distance between individuals without taking elevation into account. In combination with previous phenotypic analyses, our results imply that ecological divergence likely plays a key role in shaping genetic structure within saltmarsh species. Comparison of restored and natural saltmarsh indicated that interspecific competition plays an important role in shaping the genetic structure observed on the natural saltmarsh. The results of this study demonstrate that saltmarshes are valuable models in which to test effects of ecological differentiation and, by extension, provide a better understanding of the functioning of this threatened environment