Founder effects, post-introduction evolution and phenotypic plasticity contribute to invasion success of a genetically impoverished invader
Multiple mechanisms may act synergistically to promote success of invasive plants. Here, we tested the roles of three non-mutually exclusive mechanisms—founder effects, post-introduction evolution and phenotypic plasticity—in promoting invasion of Chromolaena odorata. We performed a common garden experiment to investigate phenotypic diversification and phenotypic plasticity of the genetically impoverished invader in response to two rainfall treatments (ambient and 50% rainfall). We used ancestor–descendant comparisons to determine post-introduction evolution and the QST-FST approach to estimate past selection on phenotypic traits. We found that eight traits differed significantly between plants from the invasive versus native ranges, for two of which founder effects can be inferred and for six of which post-introduction evolution can be inferred. The invader experienced strong diversifying selection in the invasive range and showed clinal variations in six traits along water and/or temperature gradients. These clinal variations are likely attributed to post-introduction evolution rather than multiple introductions of pre-adapted genotypes, as most of the clinal variations were absent or in opposite directions from those for native populations. Compared with populations, rainfall treatments explained only small proportions of total variations in all studied traits for plants from both ranges, highlighting the importance of heritable phenotypic differentiation. In addition, phenotypic plasticity was similar for plants from both ranges although neutral genetic diversity was much lower for plants from the invasive range. Our results showed that founder effects, post-introduction evolution and phenotypic plasticity may function synergistically in promoting invasion success of C. odorata.
KeywordsAncestor–descendant comparisons Chromolaena odorata Clinal changes Invasion mechanisms Local adaptation QST-FST approach Water stress
We are grateful to Xiangqing Yu and Xiaona Shao for providing molecular data; Isabel Mück and Phillip Gienapp for sharing R code; Madalin Parepa for suggestions on data analysis. This work was supported by the National Key R&D Program of China (2017YFC1200101, 2016YFC1201100), the National Natural Science Foundation of China (31500463, 31470575, 31670545, 31270582), and a scholarship from the China Scholarship Council (201504910498).
Author contribution statement
ZYL and YLF conceived the ideas and designed experiments; ZYL, YLZ, WBW and QML collected the data; ZYL, JFS, and YLF analysed the data; ZYL wrote the first draft, with further inputs from JFS, YLZ and YLF.
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