Abstract
Hybridization is one of the fundamental mechanisms by which rapid evolution can occur in exotic species. If hybrids show increased vigour, this could significantly contribute to invasion success. Here, we compared the success of the two invasive knotweeds, Fallopia japonica and F. sachalinensis, and their hybrid, F. × bohemica, in competing against experimental communities of native plants. Using plant material from multiple clones of each taxon collected across a latitudinal gradient in Central Europe, we found that knotweed hybrids performed significantly better in competition with a native community and that they more strongly reduced the growth of the native plants. One of the parental species, F. sachalinensis, regenerated significantly less well from rhizomes, and this difference disappeared if activated carbon was added to the substrate, which suggests allelopathic inhibition of F. sachalinensis regeneration by native plants. We found substantial within-taxon variation in competitive success in all knotweed taxa, but variation was generally greatest in the hybrid. Interestingly, there was also significant variation within the genetically uniform F. japonica, possibly reflecting epigenetic differences. Our study shows that invasive knotweed hybrids are indeed more competitive than their parents and that hybridization increased the invasiveness of the exotic knotweed complex.
Highlights
Hybridization is an important and common evolutionary process in plants and animals (Arnold 2004)
Previous studies that compared the invasiveness of hybrids to that of their parents found that hybrids can be more plastic and more tolerant to environmental conditions (Weber and D’Antonio 1999), better competitors against native plants (Daehler and Strong 1997) or spreading faster than parents (Vila and D’Antonio 1998; Hovick et al 2012)
Addition of activated carbon generally improved knotweed regeneration, and this effect was strong for F. sachalinensis, where addition of AC increased regeneration by more than 50% (Fig. 1A)
Summary
Hybridization is an important and common evolutionary process in plants and animals (Arnold 2004). Oftentimes, the rapid spread and resulting ecological and economic problems of invasive species only begin after a lag phase (Ewel et al 1999; Crooks 2005), possibly because these species first undergo evolutionary changes (Sakai et al 2001; Lee 2002; Bossdorf et al 2005; Suarez and Tsutsui 2008) For some of these species, these may be inter- or intraspecific hybridization events. Previous studies that compared the invasiveness of hybrids to that of their parents found that hybrids can be more plastic and more tolerant to environmental conditions (Weber and D’Antonio 1999), better competitors against native plants (Daehler and Strong 1997) or spreading faster than parents (Vila and D’Antonio 1998; Hovick et al 2012). Such direct comparisons of invasive hybrids and their parents remain scarce
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