China-US grain trade shapes the spatial genetic pattern of common ragweed in East China cities

Abstract

Common ragweed is an invasive alien species causing severe allergies in urban residents. Understanding its urban invasion pathways is crucial for effective control. However, knowledge is limited, with most studies focusing on agricultural and natural areas, and occurrence record-based studies exhibiting uncertainties. We address this gap through a study in East China cities, combining population genetics and occurrence records. Leaf samples from 37 urban common ragweed populations across 15 cities are collected. Genomic and chloroplast DNA extraction facilitate analysis of spatial genetic patterns and gene flows. Additionally, international grain trade data is examined to trace invasion sources. Results indicate spatial genetic patterns impacted by multiple introductions over time. We infer the modern grain trade between the United States and China as the primary invasion pathway. Also, cities act as transportation hubs and ports of grain importation might disperse common ragweed to urban areas. Invasive species control should account for cities as potential landing and spread hubs of common ragweed.

Fig. 1. Geographical patterns of cpDNA haplotypes in East China cities.

a Study area. b Genetic patterns, the color proportions of the pie indicated the frequency of each cpDNA haplotype in the population. Abbreviations: Mudanjiang (MDJ), Changchun (CC), Shenyang (SY), Fushun (FS), Qinhuangdao (QHD), Beijing (BJ), Qingdao (QD), Shanghai (SH), Nanjing (NJ), Wuhan (WH), Changsha (CS), Fuzhou (FZ), Guangzhou (GZ), Chongqing (CQ), Guiyang (GY). Numbers are ids of the populations collected in the city.

Fig. 2. Genetic clusters of the populations of common ragweed in East China cities were inferred using relative probabilities of assignment to genetic clusters in STRUCTURE.

Bar heights represent the relative probability of assignment of individual plants to varying numbers of genetic clusters. Genetic clusters identified by GENELAND were indicated by letters. Abbreviations are names of sampled cities and populations: Mudanjiang (MDJ), Changchun (CC), Shenyang (SY), Fushun (FS), Qinhuangdao (QHD), Beijing (BJ), Qingdao (QD), Shanghai (SH), Nanjing (NJ), Wuhan (WH), Changsha (CS), Fuzhou (FZ), Guangzhou (GZ), Chongqing (CQ), Guiyang (GY).

Fig. 3. Directed weighted population genetic graph.

a Study area. b Genetic graph, arrow indicates the direction of gene flow, and the width of the edge is weighted by the migration rate. The numbers underneath the city are values of strength, which measure the centrality of the genetic graph.

Fig. 4

The first observation time (20-year scale) of common ragweed in different regions of China.

Fig. 5. Annual grain imports in East China cities from 2000 to 2006.

Horizontal black bars represent the median value. Box limits indicate 75% and 25% quartiles. Whiskers indicated the minimum and maximum value. The white point indicated the mean value. The sample size for each city is 7 (n = 7). Abbreviations are names of sampled cities: Mudanjiang (MDJ), Changchun (CC), Shenyang (SY), Fushun (FS), Qinhuangdao (QHD), Beijing (BJ), Qingdao (QD), Shanghai (SH), Nanjing (NJ), Wuhan (WH), Changsha (CS), Fuzhou (FZ), Guangzhou (GZ), Chongqing (CQ), and Guiyang (GY). (Source: EPS CHINA DATA).