Rapid Evolution in Introduced Plant Species

Abstract

Evolution was once seen as a process that acted only on timescales of thousands to millions of years. Recent studies demonstrating rapid evolutionary change over periods of tens to hundreds of years show that that evolutionary change can occur during a human lifetime. Most examples come from the study of introduced species. Despite having examples of rapid evolution occurring in a wide variety of introduced taxa, we lack information about how often that introduced species undergo rapid evolutionary change in their new range. However, an understanding of what proportion of pant species undergo rapid evolutionary change in response to novel environmental conditions (such as those experienced by introduced species) is important for understanding plant invasion, as well as the way plant species respond to temporal environmental change. In this study we provide one of the first tests of how common rapid evolution is, using herbarium specimens to track morphological change through time in plant species introduced to New Zealand and New South Wales, Australia. Our results suggest that rapid evolution in introduced plant species could be much more common than previously thought. Of our 23 study species in Australia, 70% showed evidence of change in morphology over time. In New Zealand, 47% of 17 species showed evidence of change. The magnitude of the changes we found is surprisingly high, reaching as much as 216%. We asked whether any factors could be used to predict the magnitude of these changes. We found no relationship between the magnitude of change and lifespan, number of native congeners, plant height, or position in the phylogenetic tree. Overall, this suggests that a high proportion and a wide variety of plant species are able to respond to environmental change on short timescales.