Genetic diversity of the newly invasive weed Flaveria bidentis (Asteraceae) reveals consequences of its rapid range expansion in northern China

Abstract

Ma JW, Geng SL, Wang SB, Zhang GL, Fu WD & Shu B (2011). Genetic diversity of the newly invasive weed Flaveria bidentis (Asteraceae) reveals consequences of its rapid range expansion in northern China. Weed Research51, 363–372. Summary The South American weed Flaveria bidentis has spread rapidly across northern China since its introduction to the Tianjin area in 2001. To explore its introduction dynamics and mechanism of rapid range expansion in northern China, we examined genetic diversity in 26 populations across the invaded range, using inter‐simple sequence repeat markers. We found relatively high intraspecies genetic diversity (He = 0.279; I = 0.415) and wide‐ranging genetic variation within populations (He = 0.095–0.263; I = 0.160–0.383), with relatively high genetic diversity in both older established populations and some newly established populations. Approximately 78% of genetic variation resides within populations, according to analysis of molecular variance. The unweighted pair group method with arithmetic mean clustered populations into two groups, composed of most populations distributed along the G106 or G107 National Roads. Moreover, a Mantel test showed no significant correlation between geographical and genetic distances. The findings indicate that during F. bidentis invasion, sexual reproduction and multiple introductions have maintained high genetic diversity, while secondary introductions or admixtures of populations have mitigated losses of genetic variation caused by founder events and promoted local adaptation and colonisation. In addition, human‐mediated long‐distance seed dispersal, via National Roads, may have contributed to its weak geographical genetic structure and rapid range expansion in northern China. To prevent further introductions, imports should be monitored at Tianjin (the likely first arrival point). To control established populations, efforts should focus on populations with high genetic diversity, populations along the G106 and G107 National Roads and regions that are climatically similar to its native range.

Genetic variation in the invasive weedMikania micrantha(Asteraceae) suggests highways as corridors for its dispersal in southern China

“…The values were much higher than in several other invasive species of Asteraceae in China Tang et al, 2009;Ma et al, 2011), and were even higher than in a previous study using inter-SSR (ISSR) markers for this species in southern China (Wang et al, 2008). Although SSR markers could reveal much more genetic variation than ISSRs, the results were unexpected for these roadside populations, which had short invasive histories (10-20 years).…”

“…The AMOVA indicated that most of the genetic variation (91 %) resided within populations, rather than among populations (9 %) or among regions (highways, 0 %). The level of genetic differentiation among populations (F ST ¼ 0Á044, P < 0Á01) was much lower than the values reported for several other invasive species of Asteraceae in China Tang et al, 2009;Ma et al, 2011). Considering that the populations studied were located on the roadsides of four highways (from different directions) and were at least 40 km apart from each other, such a low level of genetic differentiation among populations was surprising.…”

“…Even though roads may be important contributing factors in biological invasions, their precise roles in the spatial spread of alien species remain poorly understood (Dar et al, 2015). Investigations into the genetic variation of roadside populations are essential for understanding their patterns and pathways of dispersal because genetic and evolutionary processes may be the keys to whether invasive species are established and spread (Sakai et al, 2001;Ma et al, 2011).…”

“…In Guangdong Province, which is the main distribution region of M. micrantha in southern China, the highway network extends over a large area. Road construction, maintenance operations and transportation have major impacts on the colonization and spread of invasive species (Trombulak and Frissell, 2000;Hawbaker et al, 2005;Ma et al, 2011;Dar et al, 2015). The seeds of M. micrantha can be carried to other places by adhering to vehicles, and the invasive species can complete the colonization of roadsides using released seeds.…”

“…First, if the weeds' expansion along highways was driven mainly by natural forces (presumably by wind, as this species produces typical achene-pappus units), then it would be restricted to short-distance (step-by-step) dispersal and would experience a series of population bottlenecks and genetic drift during colonization. Reductions in both allelic richness (AR) and genetic diversity would be expected for the roadside populations as the distance from Shenzheng (the first area invaded in mainland China by M. micrantha) increased (Hassel et al, 2005;Ma et al, 2011;Li and Geng, 2015). Second, if the expansion was facilitated by anthropogenic activity (vehicle transportation), then the weed would undergo long-distance dispersal.…”