Genetic Diversity, Ecotype Hybrid, and Mixture of Invasive Spartina alterniflora Loisel in Coastal China

Spartina alterniflora, a native species at the east coast of North America, is currently the focus of increasing management concern due to its rapid expansion in coastal China. To better understand the plant traits associated with the success of invasion, we examined the genetic variation and the possible existence and distribution of ecotype hybrids and ecotype mixtures of the species in China. We collected and analyzed 144 samples from seven populations throughout coastal China (21.6 degrees-38.6 degrees N; 109.7 degrees-121.8 degrees E) using amplified fragment length polymorphisms markers. The results indicated that the genetic diversity of S. alterniflora in China was low, with a percentage of polymorphic bands (PPB) = 23.24%, heterozygosity (HE) = 0.2979 and the average diversity within populations = 0.4427 at the population level, as well as PPB = 28.07%, HE = 0.3743 and the total diversity of the species = 0.5520 at the species level. The majority of the variation was found within rather than among populations, as estimated by Nei's genetic diversity (20.39%), Shannon's index (19.80%) and analysis of molecular variance (23.56%). Results of assignment show that both ecotype hybrids and ecotype mixtures exist in coastal China, especially in southern populations. Therefore, the species' success in coastal China may be attributable largely to the coexistence of various ecotype hybrids and ecotype mixtures resulting from three independent introductions of the species' three ecotypes from their native ranges coupled with increasing human disturbances in the region.