Invasive and Non-Invasive Congeners Show Similar Trait Shifts between Their Same Native and Non-Native Ranges Yedra Garcı´a 1 *, Ragan M. Callaway 2 , Alecu Diaconu 3 , Daniel Montesinos 1,2,4 1 Centre for Functional Ecology, Universidade de Coimbra, Coimbra, Portugal, 2 Division of Biological Sciences, University of Montana, Missoula, Montana, United States of America, 3 Biological Control Laboratory, Institute of Biological Research Ias ¸i, Ias ¸i, Romania, 4 Centro de Investigaciones sobre desertificacio ´ n (CIDE CSIC-UV-GV), Montcada, Vale `ncia, Spain 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. Citation: Garcı ´a Y, Callaway RM, Diaconu A, Montesinos D (2013) Invasive and Non-Invasive Congeners Show Similar Trait Shifts between Their Same Native and Non-Native Ranges. PLoS ONE 8(12): e82281. doi:10.1371/journal.pone.0082281 Editor: Antonietta Quigg, Texas A&M University, United States of America Received June 18, 2013; Accepted October 22, 2013; Published December 17, 2013 Copyright: ß 2013 Garcı ´a et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: RMC was funded by NSF-DEB 0614406 and thanks NSF EPSCoR; DM was funded by the Spanish Micinn (2008-0662), by the Portuguese FCT (SFRH/BPD/ 72595/2010), and by a Marie Curie Career Integration Grant (FP7-321909); YG was funded by DM’s MC-CIG (FP7-321909). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: yedragg@gmail.com Introduction Many exotic organisms become much more abundant and have greater impact on other species in their non-native than in their native ranges [1], [2]. Many of these invasive species have been shown to evolve different trait expression in their non-native ranges [3–5]. These changes can be due to adaptation, genetic drift, hybridization and/or founder effects [6] and have the potential to contribute substantially to invasion. However, whether these changes cause invasive success is speculative. An opportunity to explore the causal link between morphological changes and invasion is to compare shifts expressed by exotic invasive species to those of exotic congeners that naturalize in their new habitats without becoming unusually abundant or having strong impacts [7], [8]. Comparing the traits of exotic species that differ in their ability to invade may help to understand the mechanisms that promote invasion [9–11]; but there have been fewer studies focusing on differences among exotic invasive and exotic non-invasive species [12–18]. Thus the combination of both approaches: 1) the study of exotic invasive and exotic non-invasive species, and 2) studying them in both their native and non-native ranges, has a great deal of potential to shed light on traits that might be important for invasive success and, perhaps more importantly, which adaptive trait shifts between native and non-native ranges may contribute the most to an exotic species evolving in a way to become more invasive [19]. A substantial body of literature shows a strong and general tendency for plants from populations in their non-native ranges to increase in size, germination rate, and reproductive output when compared with their native ranges [4–6], [20–25]. In turn, a less common response is the loss of herbivore defensive capacity by plants in non-native ranges [26–28], but when this occurs it is interpreted in the context of tradeoffs (the hypothesis of evolution of increased competitive ability, EICA) [20]. These evolutionary tradeoffs provide a major hypothesis for how exotic species might transform into invaders; however, to our knowledge there have PLOS ONE | www.plosone.org 1 December 2013 | Volume 8 | Issue 12 | e82281