Aims Possible shifts in the phenotypic performance along invasive plants' spreading route are rarely examined due to the discontinuous and incomplete records of exotic species. As the invasion history of common ragweed (Ambrosia artemisiifolia L.) is well documented in Hungary, its residence time is known for each location. By sampling a sequence of older to more recently established populations, we aimed to determine (i) whether there are phenotypic divergences along the historical spreading route of A.artemisiifolia; (ii) which traits are under selection during the invasion process and (iii) the extent of maternal effects on the individual's performance.
Methods We used a hierarchical sampling design to collect seeds from 64 individuals belonging to eight sites in four residence time categories (seven populations along the historical spreading route of ragweed in Hungary and one recently invaded site in Romania). We selected four large and four small individual plants in each population to control for maternal effects. The offspring were reared in a common garden located in Romania. Five vegetative phenotypic traits were measured at the end of the experiments and used in the subsequent analysis (plant height, basal diameter, number of secondary axes, length of the longest secondary axis and biomass). To summarize the variation of these highly correlated traits, principal component analysis was performed first and then the important components were used in linear mixed effect models.
Important findings The residence time categories were significantly distinguished by the first component, which compresses the variation of all five measured traits. The measures gradually decrease from populations with the longest residence time (introduced more than 65 years ago) towards the most recently established populations (established less than 30 years ago). These differences might reflect the invasion history of the populations: the longer the residence time the higher the chance to develop relevant traits beneficial in invasion process. The size of the mother plant significantly influenced not only the seed mass (inversely) but also the adult performance of its offspring (directly).