Differential germination strategies of native and introduced populations of the invasive species Plantago virginica.
Germination strategies are critically important for the survival, establishment and spread of plant species. Although many plant traits related to invasiveness have been broadly studied, the earliest part of the life cycle, germination, has received relatively little attention. Here, we compared the germination patterns between native (North America) and introduced (China) populations of Plantago virginica for four consecutive years to examine whether there has been adaptive differentiation in germination traits and how these traits are related to local climatic conditions. We found that the introduced populations of P. virginica had significantly higher germination percentages and faster and shorter durations of germination than native populations. Critically, the native populations had a significantly larger proportion of seeds that stayed dormant in all four years, with only 60% of seeds germinating in year 1 (compared to >95% in introduced populations). These results demonstrate striking differences in germination strategies between native and introduced populations which may contribute to their successful invasion. Moreover, the germination strategy of P. virginica in their native range exhibited clear geographical variation across populations, with trends towards higher germination percentages at higher latitudes and lower annual mean temperatures and annual precipitation. In the introduced range, however, their germination strategies were more conserved, with less variation amongst populations, suggesting that P. virginica may have experienced strong selection for earlier life history characteristics. Our findings highlight the need to examine the role of rapid evolution of germination traits in facilitating plant invasion.