Invasive Mahonia plants outgrow their native relatives

Abstract

Invasive populations often grow more vigorously than conspecific populations in the native range. This has frequently been attributed to evolutionary changes resulting either from founder effects, or from natural selection owing to enemy release. Another mechanism contributing to evolutionary change has largely been neglected in the past: Many invasive plant species do actually descend from cultivated plants and were therefore subject to breeding, including hybridization and artificial selection. In a common garden experiment, we compared invasive Central European populations of the ornamental shrub, Mahonia, with native populations of its putative parental species, Mahonia aquifolium and M. repens, from North America. We hypothesized that plants of invasive populations show increased growth and retained high levels of heritable variation in phenotypic traits. Indeed, invasive Mahonia plants grew larger in terms of stem length, number of leaves and aboveground biomass than either of the two native species, which did not differ significantly from each other. Since there are no hints on release of invasive Mahonia populations from natural enemies, it is likely that hybridization and subsequent selection by breeders have lead to an evolutionary increase of plant vigour in the introduced range. Further on, heritable variation was not consistently reduced in invasive populations compared with populations of the two native species. We suggest that interspecific hybridization among the Mahonia species has counteracted the harmful effects of genetic bottlenecks often associated with species introductions. Based on this case study, we conclude that, more attention has to be paid on the role of plant breeding when assessing the mechanisms behind successful plant invasions in future.

Why Mahonia? Molecular recircumscription of Berberis s.l., with the description of two new genera, Alloberberis and Moranothamnus

“…(2015) advocated a broadly circumscribed Berberis to include Mahonia; however, the adoption of Berberis s.l. is far from universal (e.g., Wang & al., 2007;Ross & Auge, 2008;Wu & al., 2009;Ying & al., 2011;Holmgren & Holmgren, 2012;Ma & al., 2013;Zhao & al., 2013). For example, while in Flora of North America Whittemore (1997) adopted Berberis s.l., stating that "Mahonia is often recognized in horticultural works, but it is seldom recognized by botanists", Holmgren & Holmgren (2012) in the Intermontain Flora maintained "Mahonia as an easily recognized group worthy of generic distinction.…”

Larval settlement behaviour in six gregarious ascidians in relation to adult distribution

“…Propagule pressure, defined as the combined effect of the number of individuals introduced and the number of introduction attempts, has been identified as an important predictor of invasiveness of non-native species (Colautti et al 2006). Because conditions for propagule establishment and development often differ between the native and invaded ranges, most invasive species perform differently in localities to which they are introduced, where they are often more abundant (DeWalt et al 2004, Kasper et al 2008, larger (Ross & Auge 2008), comparatively free of predators (Wolfe 2002), less prone to parasitism (Calvo-Ugarteburu & McQuaid 1998) and have a higher reproductive output (Hinz & Schwarzlaender 2004). Moreover, invasive species generally show a strongly aggregated distribution (Kopin et al 2001, Dulloo et al 2002, Campbell & Donlan 2005, Dupont et al 2006 and form large monospecific stands that can monopolise available habitat (Simberloff et al 2005, Rius et al 2009a.…”

Hybrid Vigor for the Invasive Exotic Brazilian Peppertree (Schinus terebinthifoliusRaddi., Anacardiaceae) in Florida

“…Our experimental protocol, however, allowed us to test for differences among the three types found in Florida. The result of reproductive superiority of hybrid individuals (i.e., most often the F 1 generation) to their progenitors has been found in other species (for reviews, see Arnold and Hodges 1995;Gaskin and Schaal 2002;Ainouche et al 2003;Rhode and Cruzan 2005;Campbell et al 2006;Rieseberg et al 2007;Ross and Auge 2008) and can contribute to the hybrid's greater fitness. The germination of a greater number of seeds provides the filtering process of more fit genotypes via natural selection, additional raw material (i.e., seedlings).…”

“…In other words, the hybrid seedlings not only had greater survival rates (i.e., reached higher per-pot densities), but they also attained greater biomass than the western seedlings. Several recent studies on interspecific hybrids have shown greater vegetative growth of hybrids compared to parental genotypes (Vila and D'Antonio 1998;Erfmeier and Bruelheide 2005;Ross and Auge 2008). The ultimate fitness consequence of greater early vegetative growth is difficult to gauge as fitness for perennial organisms relies on measuring lifetime reproductive success (Rhode and Cruzan 2005).…”