Investigating the effects of whole genome duplication on phenotypic plasticity: Implications for the invasion success of Giant Goldenrod (Solidago gigantea)

Polyploidy commonly occurs in invasive species and phenotypic plasticity
(PP, the ability to alter one’s phenotype in different environments), is
predicted to be enhanced in polyploids and contribute to their invasive
success. However, empirical support that increased PP is frequent in
polyploids and/or confers invasive success is limited. Here, we
investigated if polyploids are more pre-adapted to become invasive than
diploids via the scaling of trait values and PP with ploidy-level, and if
post-introduction selection has led to a divergence in trait values and PP
responses between native- and non-native cytotypes. We grew diploid,
tetraploid (from both native North American and non-native European
ranges), and hexaploid Solidago gigantea in pots outside with low, medium,
and high soil nitrogen and phosphorus (NP) amendments, and measured traits
related to growth, asexual reproduction, physiology, and insects/pathogen
resistance. We found little evidence to suggest that polyploidy and
post-selection shaped mean trait and PP responses. To examine invasion
dynamics, we compared diploids to tetraploids (as their introduction into
Europe was more likely), and found that tetraploids had greater pathogen
resistance, photosynthetic capacities, and water-use efficiencies and
generally performed better under NP enrichments. Furthermore, tetraploids
invested more into roots than shoots in low NP and into shoots than roots
in high NP and this resource strategy is beneficial under variable NP
conditions. Lastly, native-tetraploids exhibited greater plasticity in
biomass accumulation, clonal-ramet production and water-use efficiency.
Cumulatively, tetraploid S. gigantea possesses traits that might have
pre-disposed and enabled them to become successful invaders. Our findings
highlight that trait expression and invasive species dynamics are nuance
while also providing insight into the invasion success and cyto-geographic
patterning of S. gigantea that can be broadly applied to other invasive
species with polyploid complexes.

多倍体（polyploidy）在入侵物种中普遍存在，而表型可塑性（phenotypic plasticity，PP，即生物在不同环境中改变自身表型的能力）被预测在多倍体中会增强，并有助于其入侵成功。然而，关于多倍体中PP增强现象普遍存在且/或其赋予入侵成功优势的实证支持仍较为有限。在此，我们探究了多倍体是否通过性状值和PP随倍性水平（ploidy-level）的缩放，比二倍体更具成为入侵物种的预适应性；以及引入后的选择是否导致了本地和非本地细胞型（cytotypes）之间性状值和PP响应的分化。我们在室外花盆中种植了二倍体、四倍体（来自北美本地和欧洲非本地分布区）和六倍体加拿大一枝黄花（Solidago gigantea），设置了低、中、高三种土壤氮磷（NP）添加水平，并测定了与生长、无性繁殖（asexual reproduction）、生理及昆虫/病原菌抗性相关的性状。我们几乎未发现证据表明多倍体化和引入后的选择塑造了平均性状值和PP响应。为探究入侵动态，我们将二倍体与四倍体（因其更可能被引入欧洲）进行比较，发现四倍体具有更强的病原菌抗性、光合能力（photosynthetic capacities）和水分利用效率（water-use efficiencies），且在NP富集条件下表现普遍更优。此外，四倍体在低NP条件下对根的投入多于地上部分，而在高NP条件下对地上部分的投入多于根，这种资源分配策略在NP可变环境中具有优势。最后，本地四倍体在生物量积累、克隆分株产生量（clonal-ramet production）和水分利用效率方面表现出更强的可塑性。综上，四倍体加拿大一枝黄花具有可能使其预先具备优势并促成其成为成功入侵者的性状。我们的研究结果强调了性状表达和入侵物种动态的复杂性，同时为加拿大一枝黄花的入侵成功及细胞地理格局（cyto-geographic patterning）提供了见解，这些见解可广泛应用于其他具有多倍体复合体的入侵物种。