Abstract
Narrowly lanceolate leaves occur frequently in the genus Aster. It was often employed as a distinguishing character in the taxonomy of this genus. The origin of this particular leaf shape, however, has never been investigated using comparative methods. In this study, we reconstructed a comprehensive phylogeny that includes most species of Aster with narrowly lanceolate leaf. We then gathered data on riparian habitats and the presence or absence of narrowly lanceolate leaves, and investigated the evolutionary association between them in a phylogenetic context. Our analysis indicated that the species with narrowly lanceolate leaves are nested in unrelated lineages of the genus Aster, implying that they originated independently several times. Using Pagel’s comparative method of discrete data, we demonstrated a significant correlation between riparian habitats and narrowly lanceolate leaves. We further inferred the sequence of transition of the two characters. This analysis indicated that the sequence of evolution of riparian habitat and narrowly lanceolate leaf form was usually uncertain, but some positive results showed that the occurrence of riparian habitats may not precede the evolution of narrowly lanceolate leaf form. This study provided new insights into the adaptive evolution in a mega-diverse family. In addition, Aster tonglingensis, an unexpected new species with narrowly lanceolate leaves, was discovered and established based on the evidence from morphology, micromorphology and molecular phylogeny.
Highlights
How the environments modify morphology is one of the key questions in evolutionary biology (Grant & Grant, 2002; Lamichhaney et al, 2015; Malinsky & Salzburger, 2016; Meier et al, 2017)
We aim to (1) use three molecular markers to reconstruct the phylogeny of Aster to resolve the phylogenetic positions of the Aster species with narrowly lanceolate leaf and test the monophyly of the two similar species of Aster; (2) use Pagel’s trait evolution analysis methods (Pagel, 1994) to test whether the narrowly lanceolate leaf is significantly correlated with the riparian habitat, and if so to test the transformation ratio among four potential character combinations, and to determine whether the riparian habitat drives the evolution of narrowly lanceolate leaf; and (3) examine the morphological and micro-morphological characters of the distinctive Aster species from Mt
For broadly riparian habitat, p-value of likelihood ratio (LRT) of Maximum Likelihood (ML) method between two models was smaller than 0.01 and Bayes Factor of Markov Chain Monte Carlo (MCMC) method was 15.40. These results suggested that the riparian habitat and narrowly lanceolate leaf shape was strongly correlated
Summary
How the environments modify morphology is one of the key questions in evolutionary biology (Grant & Grant, 2002; Lamichhaney et al, 2015; Malinsky & Salzburger, 2016; Meier et al, 2017). Convergent evolution means that organisms from different lineages develop similar structures or forms in similar. Convergent origin of the narrowly lanceolate leaf in the genus Aster—with special reference to an unexpected discovery of a new Aster species from East China. This phenomenon is widespread in plants, such as the lotus and water lilies, or the xeric highly succulent species of Euphorbia, Cactaceae and some species of Apocynaceae (McGhee, 2011; Alvarado-Cárdenas et al, 2013)
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