Spread of invasive Phragmites australis in estuaries with differing degrees of development: genetic patterns, Allee effects and interpretation

Abstract

Summary1. The distribution of genetic variation can be interpreted to understand the timing and mechanisms of invasive species spread. Allee effects, positive relationships between fitness and density or number of conspecific individuals, can play a substantial role in determining the time lag between initial introduction and invasive spread and can produce genetic patterns in invading populations that can be interpreted to learn about factors affecting invasion mechanisms. 2. We examined the distribution of genetic variation in the invasive wetland grass Phragmites australis in the Chesapeake Bay, USA. We used microsatellite analysis to examine the reproductive mode (clonal vs. seed) by which the invasive haplotype of P. australis has spread and the distribution of genetic variation within and among brackish wetlands in nine subestuaries of the Chesapeake Bay. Watersheds associated with the subestuaries were dominated by forests, anthropogenic development or mixed forests and development. 3. Our results suggest that the invasive haplotype of P. australis has spread primarily sexually by seed, rather than clonally, and genetic diversity of patches within subestuaries increased while genetic similarity decreased with increasing development in the surrounding watershed. 4. This suggests a pattern whereby greater genetic diversity of patches may promote more rapid spread due to recruitment of multiple seedlings into a disturbed patch. 5. Synthesis. Evaluation of patterns of genetic distribution can help to identify factors affecting invasion in different environments and so inform management.

Management of invasive Phragmites australis in the Adirondacks: a cautionary tale about prospects of eradication

“…This finding is supported by others (Lombard et al 2012;Martin and Blossey 2013b) and it is likely that eradication will be even more elusive in areas with high patch connectivity (Chambers et al 1999;Kulmatiski et al 2010;McCormick et al 2010;Kettenring et al 2012Kettenring et al , 2016Hazelton et al 2014) or in areas with longer invasion histories. For example, the Michigan Department of Environmental Quality has developed a management prioritization tool (MIDEQ 2014) using multiple ecological, human values, and feasibility criteria where populations covering \100 m 2 are assigned a score of 9 and areas of 4000-80,000 m 2 a score of 5, with sites scoring higher receiving priority for management.…”

“…Seed set is variable and not all stems or even populations produce viable seed each year. But in addition to rhizome expansion and fragment transport, seeds, which are dispersed by wind, water, and adhesion to waterfowl throughout the fall and winter, are now recognized as important in dispersal and colonization of new habitats (Baldwin et al 2010;McCormick et al 2010;Albert et al 2015;Galatowitsch et al 2016;Kettenring et al 2016).…”

Increased Methane Emissions by an Introduced Phragmites australis Lineage under Global Change

“…1). Because introduced Phragmites australis exhibits tremendous genotypic variation (McCormick et al 2010;Kettenring and Mock 2012), and given the broad geographic extent of introduced Phragmites invasion (Chambers et al 1999;, our data argue for field studies that consider the consequences of genotypic variation for important ecosystem services such as carbon sequestration (Brix et al 2001). …”

Genetic and epigenetic changes during the invasion of a cosmopolitan species (Phragmites australis)

“…Unlike many invasive clonal species spreading mostly by vegetative reproduction (Gao, Geng, Li, Chen, & Yang, 2010; Lambertini et al., 2010; Richards et al., 2012), the invasion of P. australis in North America contributes to a reproduction strategy combining sexual and vegetative propagation (Albert, Brisson, Belzile, Turgeon, & Lavoie, 2015; McCormick, Kettenring, Baron, & Whigham, 2010). The high genetic diversity in P. australis makes it more difficult to detect the epigenetic changes during the invasion.…”