Invasive and Non-Invasive Congeners Show Similar Trait Shifts between Their Same Native and Non-Native Ranges

Abstract

Differences in morphological or ecological traits expressed by exotic species between their native and non-native ranges are often interpreted as evidence for adaptation to new conditions in the non-native ranges. In turn this adaptation is often hypothesized to contribute to the successful invasion of these species. There is good evidence for rapid evolution by many exotic invasives, but the extent to which these evolutionary changes actually drive invasiveness is unclear. One approach to resolving the relationship between adaptive responses and successful invasion is to compare traits between populations from the native and non-native ranges for both exotic invaders and congeners that are exotic but not invasive. We compared a suite of morphological traits that are commonly tested in the literature in the context of invasion for three very closely related species of Centaurea, all of which are sympatric in the same native and non-native ranges in Europe and North America. Of these, C. solstitialis is highly invasive whereas C. calcitrapa and C. sulphurea are not. For all three species, plants from non-native populations showed similar shifts in key traits that have been identified in other studies as important putative adaptive responses to post-introduction invasion. For example, for all three species plants from populations in non-native ranges were (i) larger and (ii) produced seeds that germinated at higher rates. In fact, the non-invasive C. calcitrapa showed the strongest trait shift between ranges. Centaurea solstitialis was the only species for which plants from the non-native range increased allocation to defensive spines, and allocated proportionally less resources to reproduction, patterns contrary to what would be predicted by theory and other empirical studies to enhance invasion. Our results suggest caution when interpreting the commonly observed increase in size and reproductive capacity as factors that cause exotics to become invaders.

Traits correlate with invasive success more than plasticity: A comparison of three Centaurea congeners

“…This is consistent with the perspective that local adaptation is a more common mechanism than phenotypic plasticity allowing plants to deal with environmental variability (Palacio‐López et al., 2015). Several studies have reported different sets of local adaptations to different non‐native ranges for several traits of the same Centaurea species studied here (García, Callaway, Diaconu, & Montesinos, 2013; Graebner, Callaway, & Montesinos, 2012; Montesinos et al., 2012). Together with our results, this suggests that local adaptation may be more important than plasticity for dealing with the new environments of the non‐native ranges for these three Centaurea species.…”

“…However, differences in growth rates did not result in differences between regions or among species in total final biomass in the controlled conditions of the greenhouse. In previous studies (García et al., 2013; Graebner et al., 2012), C. sulphurea produced the most biomass but had the lowest relative growth rates when compared to the other two species. In this study, this did not occur for control individuals.…”

Invasive and non-invasive congeneric Centaurea (Asteraceae) show contrasting patterns of herbivory by snails

“…aphids). In any case, these results should be interpreted with caution, since some trait-shifts are known to occur both in invasive and non-invasive species, and might not be necessarily responsible for invasive success, which could be better explained by a complex combination of traits (García et al 2013). …”

Inter‐regional hybrids of native and invasive Centaurea solstitialis display intermediate competitive ability

“…Despite recent focus on the rapid evolution of competitive ability by exotic invaders, little is known about its heritability. Centaurea solstitialis is an annual weed native to southern Europe, it is not involved in inter‐specific hybridization events, and has been introduced into South and North America, where it presents a number of local adaptations and became an aggressive invader (Graebner et al , Montesinos et al , García et al , Eriksen et al ). When the competitive ability of C. solstitialis plants from native Spanish and non‐native Californian populations was compared to the competitive ability of intra‐specific inter‐regional hybrids from those regions (see Supplementary material Appendix 1 for methods), we did not find differences among seed ancestries for the competitive effect of B. hordeaceus on C. solstitialis (F 3,33 = 0.648; p = 0.521).…”