High Genetic Diversity With Weak Phylogeographic Structure of the Invasive Spartina alterniflora (Poaceae) in China

Abstract

Biological invasion represents a global issue of concern due to its large negative impacts on native ecosystems and society. Elucidating the evolutionary history and genetic basis underpinning invasiveness is critical to understanding how alien species invade and adapt to novel environments. Smooth cordgrass (Spartina alterniflora, 2n = 6x = 62) is a notorious invasive species that causes heavily negative effects on native ecosystems worldwide. Here we addressed the evolutionary mechanisms underlying the invasion and dispersal history of this species along the China coast in the past decades. We employed nine microsatellites and three chloroplast fragments to investigate phylogeographic structure and genetic diversity of 11 native US and 11 invasive Chinese S. alterniflora populations. Demographic history simulation was also performed for both the native and invasive populations, respectively. Comparative genetic analyses of these natural populations revealed that although all the Chinese populations were introduced only once, high level of genetic diversity with weak geographic structure was observed. In particular, both the genetic features and mathematical simulation illustrated very recent population expansion in the Chinese populations. We found that genetic variants identified in native US populations were mixed in the Chinese populations, suggesting the recombination of these original variants during the invasion process. These genetic attributes indicate that Chinese populations might not have experienced a genetic bottleneck during the invasion process. High genetic diversity and genetic admixture might have contributed to the success of invasion of S. alterniflora in China. Our study provides a framework of how the smooth cordgrass spreads along the China coast as well as its potential genetic mechanisms underlying the invasion.

Contrasting latitudinal clines of nematode diversity in Spartina alterniflora salt marshes between native and introduced ranges

“…The following generations of S. alterniflora that were distributed across the Chinese coastline likely had little genetic variability and no genetic structure by distance, because the source populations cross‐fertilized each other and the same offspring were distributed everywhere (An et al, 2007; Bernik, Li, & Blum, 2016; Guo et al, 2015). The available evidence suggests that S. alterniflora in China has little genetic differentiation (Shang et al, 2019) and has not undergone rapid selection for most traits over the following four decades, and thus, the populations remain genetically similar across latitude (Liu, Maung‐Douglass, Strong, Pennings, & Zhang, 2016; Liu et al, 2017; Zheng, Shao, & Sun, 2018). Because plant traits are one of the major factors driving nematode community structure, along with soil characteristics and climate (Nielsen et al, 2014; van der Hoogen et al, 2019; Wu et al, 2016), the relatively genetic homogeneity of introduced S. alterniflora populations in China may explain the lack of a strong latitudinal trend in associated nematodes.…”

Subsurface aeration of tidal wetland soils: Root-system structure and aerenchyma connectivity in Spartina (Poaceae)

“…The hybrids S.  townsendii and S. anglica inhabit a wide variety of habitats and marsh zones (e.g., Gray et al, 1991;Hacker et al, 2001;Granse et al, 2020) in-and outside the parental range (e.g., Maricle et al, 2006;Wong et al, 2018;Proença et al, 2019, Granse et al, accepted). S. anglica and parental S. alterniflora have gained attention as invasive species which spread in coastal habitats around the globe (e.g., Ranwell, 1967;Strong and Ayres, 2013;Bortolus et al, 2015;Shang et al, 2019). The high affinity of both S. anglica and S. alterniflora for belowground relocated oxygen is considered to be beneficial in hypoxic soils and may increase their invasive success (Maricle et al, 2006;Maricle and Lee, 2007).…”

Epigenetics and the success of invasive plants

“…The species was also introduced to California [134], Western Europe [133], South Africa [149] and China, where its spread has been spectacular [150]. Clonal propagation seems to have contributed to the spread of this otherwise wind-pollinated perennial species in many cases ( [151,152]; but see [138,153]). Although Chinese populations appear to be genetically diverse [138,139,153], the introduction from China to Japan so far has resulted in a lack of diversity in the Japanese populations, suggesting both founder effect and predominantly clonal propagation [152].…”

“…Clonal propagation seems to have contributed to the spread of this otherwise wind-pollinated perennial species in many cases ( [151,152]; but see [138,153]). Although Chinese populations appear to be genetically diverse [138,139,153], the introduction from China to Japan so far has resulted in a lack of diversity in the Japanese populations, suggesting both founder effect and predominantly clonal propagation [152]. Other invasive Spartina species spread extensively by clonal means, such as S. patens (syn.…”

“…Even intraspecific hybridization can facilitate successful invasions through increasing genetic diversity and heterosis (e.g. S. alterniflora; [134,138,153]). Kagawa & Takimoto [208] modelled transgressive segregation in theoretical hybrid species and found that adaptive radiation into suitable novel niches was most likely to occur in hybrid offspring from parental species with moderate genetic differentiation [208,209].…”