Abstract
Species may become invasive after introduction to a new range because phenotypic traits pre-adapt them to spread and become dominant. In addition, adaptation to novel selection pressures in the introduced range may further increase their potential to become invasive. The diploid Leucanthemum vulgare and the tetraploid L. ircutianum are native to Eurasia and have been introduced to North America, but only L. vulgare has become invasive. To investigate whether phenotypic differences between the two species in Eurasia could explain the higher abundance of L. vulgare in North America and whether rapid evolution in the introduced range may have contributed to its invasion success, we grew 20 L. vulgare and 21 L. ircutianum populations from Eurasia and 21 L. vulgare populations from North America under standardized conditions and recorded performance and functional traits. In addition, we recorded morphological traits to investigate whether the two closely related species can be clearly distinguished by morphological means and to what extent morphological traits have changed in L. vulgare post-introduction. We found pronounced phenotypic differences between L. vulgare and L. ircutianum from the native range as well as between L. vulgare from the native and introduced ranges. The two species differed significantly in morphology but only moderately in functional or performance traits that could have explained the higher invasion success of L. vulgare in North America. In contrast, leaf morphology was similar between L. vulgare from the native and introduced range, but plants from North America flowered later, were larger and had more and larger flower heads than those from Eurasia. In summary, we found litte evidence that specific traits of L. vulgare may have pre-adapted this species to become more invasive than L. ircutianum, but our results indicate that rapid evolution in the introduced range likely contributed to the invasion success of L. vulgare.
Highlights
Why only certain species become invasive when introduced into new ranges and others not is still a major question in invasion biology
With the comparison of native L. vulgare and L. ircutianum we aimed to investigate whether the two species differ in performance and functional traits that may explain the higher invasion success of L. vulgare in North America and whether they can be clearly distinguished by morphology
The principal component analyses (PCAs) based on individual plants revealed a relatively clear separation of L. vulgare and L. ircutianum the variability was large and some L. vulgare plants grouped with L. ircutianum and vice versa (S5 Appendix)
Summary
Why only certain species become invasive when introduced into new ranges and others not is still a major question in invasion biology. Several studies focused on identifying traits that may pre-adapt plant species to become invasive after introduction to a new range Beside pre-adaptation, evolutionary changes in response to novel selection pressures in the introduced range may play an important role in enabling introduced plants to become invasive [11,12,13,14,15,16]. Numerous studies have investigated whether there are evolutionary changes in traits related to performance by growing plants from the native and introduced range under standardized conditions and these studies generally found evolution of increased size but only moderate or no support for the EICA hypothesis (reviewed by [14, 19]). A recent study comparing herbarium specimens of species invasive to Australia showed that five out of 19 species have undergone significant changes in leaf shape through time [13]
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