Herbivore resistance of invasive Fallopia species and their hybrids

Abstract

Hybridization has been proposed as a mechanism by which exotic plants can increase their invasiveness. By generating novel recombinants, hybridization may result in phenotypes that are better adapted to the new environment than their parental species. We experimentally assessed the resistance of five exotic Fallopia taxa, F. japonica var. japonica, F. sachalinensis and F. baldschuanica, the two hybrids F. × bohemica and F. × conollyana, and the common European plants Rumex obtusifolius and Taraxacum officinale to four native European herbivores, the slug Arion lusitanicus, the moth Noctua pronuba, the grasshopper Metrioptera roeselii and the beetle Gastrophysa viridula. Leaf area consumed and relative growth rate of the herbivores differed significantly between the Fallopia taxa and the native species, as well as among the Fallopia taxa, and was partly influenced by interspecific variation in leaf morphology and physiology. Fallopia japonica, the most abundant Fallopia taxon in Europe, showed the highest level of resistance against all herbivores tested. The level of resistance of the hybrids compared to that of their parental species varied depending on hybrid taxon and herbivore species. Genotypes of the hybrid F. × bohemica varied significantly in herbivore resistance, but no evidence was found that hybridization has generated novel recombinants that are inherently better defended against resident herbivores than their parental species, thereby increasing the hybrid's invasion success. In general, exotic Fallopia taxa showed higher levels of herbivore resistance than the two native plant species, suggesting that both parental and hybrid Fallopia taxa largely escape from herbivory in Europe.

Hybridization increases invasive knotweed success

“…It is unclear whether this is an inherent characteristic of the giant knotweed or a result of its lower investment into chemical defences (Krebs et al. ), because addition of activated carbon eliminated these differences in our experiment. This suggests that some kind of root exudates must be involved, either exudates of F. sachalinensis that stimulate the activity of soil pathogens or exudates of other species with similar effects.…”

Biogeographic comparisons of herbivore attack, growth and impact of Japanese knotweed between Japan and France

“…Based on the identified taxa, we found that the French invertebrate communities were as diverse as the Japanese ones, but with marked differences in composition: herbivores formed an important part of the fauna sampled on Japanese plants, whereas there were almost none on French plants, either because they failed to grow on F. japonica (Tallamy, Ballard & D'Amico ) or because they avoided F. japonica patches because of unpalatable leaves (Krebs et al . ). Surprisingly, we sampled only generalist herbivores, even in Japan, while specialist species are usually dominant (Bernays & Graham ).…”

Hybridization of an invasive shrub affects tolerance and resistance to defoliation by a biological control agent

“…; McGuire and Johnson ; Krebs et al. ). A possible mechanism for these differences is novel chemistry of hybrid host plants (Orians ).…”

“…; Krebs et al. ). In invasive plant systems, hybridization can affect the frequency of herbivore attack, especially when hybrids are compared as a group to their parent species (Blair et al.…”

“…How biological control is affected by invasive plant hybridization and other evolutionary mechanisms remains largely unknown (Muller-Scharer et al 2004). In native systems, herbivores can distinguish among hybrid genotypes (Fritz et al 1998;McGuire and Johnson 2006), and hybrid plants can have more or less resistance to attack compared with their parent species (Whitham 1989;Fritz et al 1999;Krebs et al 2011). In invasive plant systems, hybridization can affect the frequency of herbivore attack, especially when hybrids are compared as a group to their parent species (Blair et al 2008;Krebs et al 2011;Cuda et al 2012).…”