A phylogenetic subclade analysis of range sizes of endemic woody seed plant species of China: Trait conservatism, diversification rates and evolutionary models

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Abstract

Adaptive radiation predicted that diversification rate of species and/or the divergence of trait evolution are declined from ancient to contemporary time due to reduced novel niches, namely the “early burst” model. It is still controversial whether the early burst model is ubiquitous over various taxa for species diversification and/or phenotypic evolution. The applicability of the model on plants has little been tested yet in current literature. To address this question, in the present study, a subclade-level phylogenetic comparative analysis of range size evolution and diversification rates of 6885 endemic woody seed plant species in China (i.e., species only found in China) was performed. My study showed that phylogenetic signals of range sizes depend on the phylogenetic scope and the sampling of subclades. Early burst model was not supported for the range size evolution for endemic woody plants of China, while the simple Brownian motion model of adaptive radiation had the best fit. Diversification of species over the subclades of the phylogeny showed that young clades have higher diversification rates than old clades, being contradictory to the “early burst” prediction of adaptive radiation. However, a whole-phylogeny diversification analysis suggests that the BOTHVAR model where speciation rate is decreasing while extinction rate is increasing is the best one to describe the time-dependent trend of diversification of endemic woody plants of China. Moreover, the evolution of range sizes of woody plants is found to be largely independent to diversification rates of species, deprecating the positive range sizes-diversification hypothesis. At last, a strong positive relationship between phylogenetic mean and variance of range sizes was observed. In conclusion, the “early burst” model predicted by adaptive radiation might be applied to the diversification rates, but not the range size evolution of endemic woody plants of China. Further studies are required by sampling more taxa and building a high-quality phylogeny to test and verify the patterns found in the present study.

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