No Evolutionary Shift in the Mating System of North American Ambrosia artemisiifolia (Asteraceae) Following Its Introduction to China

The mating system plays a key role during the process of plant invasion. Contemporary evolution of uniparental reproduction (selfing or asexuality) can relieve the challenges of mate limitation in colonizing populations by providing reproductive assurance. Here we examined aspects of the genetics of colonization in Ambrosia artemisiifolia, a North American native that is invasive in China. This species has been found to possess a strong self-incompatibility system and have high outcrossing rates in North America and we examined whether there has been an evolutionary shift towards the dependence on selfing in the introduced range. Specifically, we estimated outcrossing rates in one native and five invasive populations and compared levels of genetic diversity between North America and China. Based on six microsatellite loci we found that, like the native North American population, all five Chinese populations possessed a completely outcrossing mating system. The estimates of paternity correlations were low, ranging from 0.028–0.122, which suggests that populations possessed ∼8–36 pollen donor parents contributing to each maternal plant in the invasive populations. High levels of genetic diversity for both native and invasive populations were found with the unbiased estimate of gene diversity ranging from 0.262–0.289 for both geographic ranges based on AFLP markers. Our results demonstrate that there has been no evolutionary shift from outcrossing to selfing during A. artemisiifolia's invasion of China. Furthermore, high levels of genetic variation in North America and China indicate that there has been no erosion of genetic variance due to a bottleneck during the introduction process. We suggest that the successful invasion of A. artemisiifolia into Asia was facilitated by repeated introductions from multiple source populations in the native range creating a diverse gene pool within Chinese populations

Gene-flow through space and time: dispersal, dormancy and adaptation to changing environments

© 2015, Springer International Publishing Switzerland.Dispersal through space or time (via dormancy) determines gene flow and influences demography. Because of their functional similarities, a covariation between dispersal and dormancy is expected. Dispersal and dormancy are anatomically linked in plants, because they both depend on attributes of the seed, albeit this anatomical association is rarely considered when analyzing interactions between dispersal and dormancy. In this paper, we investigate the extent to which dispersal and dormancy can be expected to correlate and how each might influence adaptation to novel environments such as those brought on by climate change. We review the theoretical and empirical literature on the subject with a focus on seed plants. We find that although a negative correlation between dispersal and dormancy has been theoretically anticipated, several models predict deviations from this expectation under scenarios of environmental heterogeneity. The empirical evidence does not support any specific covariation pattern, likely because the interaction between dispersal and dormancy is affected by multiple environmental and developmental constraints. From a climate change perspective, the effects of dispersal and dormancy on population structure are not equivalent: dormancy-mediated gene flow is intrinsically asymmetric (from the past towards the future) whereas spatial dispersal is not necessarily directional. As a result, selection on traits linked to dormancy and dispersal might differ qualitatively. In particular, gene flow through dormancy can only be adaptive if future environmental conditions are similar to those of the past, or if it contributes to novel allelic combinations. We conclude that, in spite of a long tradition of research, we are unable to anticipate a universal relationship between dispersal and dormancy. More work is needed to predict the relative contributions of spatial dispersal and dormancy to gene flow and adaptation to novel environments