Aquatic plant invasions are often associated with long-distance dispersal of vegetative propagules and prolific clonal reproduction. These reproductive features, combined with genetic bottlenecks, have the potential to severely limit genetic diversity in invasive populations. We addressed this question in a global scale population genetic survey, using AFLP markers, of the world’s most successful aquatic plant invader, Eichhornia crassipes (water hyacinth). Our study had three main objectives: (i) to corroborate whether the worldwide spread of E. crassipes has been associated with founder events and a loss of diversity compared with the native range; (ii) to investigate if colonization of the introduced range involved more than one introduction; (iii) to evaluate whether populations in the introduced range are reproducing exclusively by clonal propagation. To our knowledge, this study represents the first global population genetic survey of a highly clonal invasive flowering plant.
Results/Conclusions
We sampled 1140 ramets from 54 populations from the native (South America) and introduced range (Asia, Africa, Europe, North America, Central America and the Caribbean). Although we detected 49 clones, introduced populations exhibited very low genetic diversity and genetic differentiation compared to native populations. 80% percent of the introduced populations were composed of a single clone. A widespread clone (W) detected in two Peruvian populations accounted for 70.9% of the individuals sampled and dominated in 74.5% of the introduced populations. However, samples from Bangladesh and Indonesia were composed of different genotypes, implicating multiple introduction events. There was clonal diversity in nine of 47 introduced populations, which suggests that sexual recruitment occurs at least in some invasive sites, presumably where environmental conditions favor seedling establishment. The global patterns of genetic diversity in E. crassipes likely result from severe genetic bottlenecks during colonization and prolific clonal propagation. The prevalence of the W genotype throughout the invasive range may be explained by stochastic sampling, or by pre-adaptation of the W genotype to low temperatures.