Herbarium specimens reveal a historical shift in phylogeographic structure of common ragweed during native range disturbance.
Invasive plants provide ample opportunity to study evolutionary shifts that occur after introduction to novel environments. However, although genetic characters pre-dating introduction can be important determinants of later success, large-scale investigations of historical genetic structure have not been feasible. Common ragweed (Ambrosia artemisiifolia L.) is an invasive weed native to North America that is known for its allergenic pollen. Palynological records from sediment cores indicate that this species was uncommon before European colonization of North America, and ragweed populations expanded rapidly as settlers deforested the landscape on a massive scale, later becoming an aggressive invasive with populations established globally. Towards a direct comparison of genetic structure now and during intense anthropogenic disturbance of the late 19th century, we sampled 45 natural populations of common ragweed across its native range as well as historical herbarium specimens collected up to 140 years ago. Bayesian clustering analyses of 453 modern and 473 historical samples genotyped at three chloroplast spacer regions and six nuclear microsatellite loci reveal that historical ragweed's spatial genetic structure mirrors both the palaeo-record of Ambrosia pollen deposition and the historical pattern of agricultural density across the landscape. Furthermore, for unknown reasons, this spatial genetic pattern has changed substantially in the intervening years. Following on previous work relating morphology and genetic expression between plants collected from eastern North America and Western Europe, we speculate that the cluster associated with humans' rapid transformation of the landscape is a likely source of these aggressive invasive populations.
Centre for GeoGenetics, University of Copenhagen, Øster Voldgade 5-7, Copenhagen K, 1350, Denmark; Department of Botany, National Museum of Natural History, MRC 166, Smithsonian Institution, Washington, DC, 20013-7012, USA; Department of Geography and Environmental Engineering, Johns Hopkins University, 313 Ames Hall, 3400 North Charles Street, Baltimore, MD, 21218, USA.
Michael D
MD
Martin
Elizabeth A
EA
Zimmer
Morten T
MT
Olsen
Andrew D
AD
Foote
M Thomas P
MT
Gilbert
Grace S
GS
Brush
D000383:Agriculture; D031164:Ambrosia / Q000235:genetics*; D001499:Bayes Theorem; D016000:Cluster Analysis; D018742:DNA, Chloroplast / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D021903:DNA, Ribosomal Spacer / Q000235:genetics; D005060:Europe; D019143:Evolution, Molecular; D058865:Introduced Species; D018895:Microsatellite Repeats; D008969:Molecular Sequence Data; D058974:Phylogeography; D017422:Sequence Analysis, DNA; D062211:Spatio-Temporal Analysis
D018742:DNA, Chloroplast; D018744:DNA, Plant; D021903:DNA, Ribosomal Spacer
contemporary evolution; hybridization; invasive species; landscape genetics; phylogeography; population genetics-empirical