Evidence for rapid adaptive evolution of phenology in the invasive grass Microstegium vimineum

Background/Question/Methods

Evolutionary dynamics of integrative traits such as phenology are predicted to be critically important to range expansion and invasion success, yet there are few empirical examples of such phenomena. In this study, we used multiple common gardens to examine the evolutionary significance of latitudinal variation in phenology of a widespread invasive species, the Asian short-day flowering annual grass Microstegium vimineum. In environmentally controlled growth chambers, we grew plants from seeds collected from multiple latitudes across the species’ invasive range. 

Results/Conclusions

Flowering time and biomass were both strongly correlated with the latitude of population origin such that populations collected from more northern latitudes flowered significantly earlier and at lower biomass than populations from southern locations. We argue that this pattern must be the result of rapid adaptive evolution of phenology over a period of less than one hundred years, and that such changes have likely promoted the northward range expansion of this species. We note that possible barriers to gene flow, including bottlenecks and inbreeding, have apparently not forestalled adaptive processes for this plant. Furthermore, we hypothesize that adaptive evolution of phenology may be widespread in many invasive plant species and an essential process during range expansion.