Cross-continental variation of herbivore resistance in a global plant invader

Abstract

PremiseAdaptation to novel biotic and abiotic environments has often been assumed in successful invasions. However, invasive species often occupy broad climatic niches within their native and introduced ranges, and a lack of invasion history and sampling bias may obscure the ability to establish how traits have changed in invasive populations from those of the origin population.MethodsWe tested heritable differences in herbivore resistance of the global invasive species,Reynoutria japonica(Japanese knotweed) by using 128 populations from both introduced (Europe and North America) and native ranges (China; Japan) in two replicated common gardens in the native range, we also explored associations between climatic and herbivore environments of the source habitats with variation in herbivore resistance within and among ranges.ResultsWe found that introduced European and North American populations were similar in all foliar resistance traits to that of native Japanese populations, but different from that of the native Chinese populations in both common gardens. On the whole, Chinese populations tended to be taller, exhibited higher LDMC and leaf C:N ratio, but lower leaf thickness, as well as leaf flavonoids compared with introduced European, North American, and native Japanese populations. In the native range, we found herbivore resistance was strongly associated with climate and herbivore pressure at the collection habitats, however, considerably few local adaptation patterns were detected in introduced European and North American populations.SynthesisOur results indicate that the introduction of certain genotypes (i.e. founder effects) played an important role in biogeographic divergence in herbivore resistance. All-purpose genotype and lack of genetically based differentiations to biotic and abiotic environmental factors might together lead to the successful invasion ofReynoutria japonicain the introduced ranges.