Dataset Information

Transcriptome analysis of two radiated Cycas species and the subsequent species delimitation of the Cycas taiwaniana complex.

ABSTRACT: Premise:Cycas is an important gymnosperm genus, and the most diverse of all cycad genera. The C. taiwaniana complex of species are morphologically similar and difficult to distinguish due to a lack of genomic resources. Methods:We characterized the transcriptomes of two closely related and endangered Cycas species endemic to Hainan, China: C. hainanensis and C. changjiangensis. Three single-copy nuclear genes in the C. taiwaniana complex were sequenced based on these transcriptomes, enabling us to evaluate the species boundaries using the multispecies coalescent method implemented in the Bayesian Phylogenetics and Phylogeography program. Results:We obtained 68,184 and 81,561 unigenes for C. changjiangensis and C. hainanensis, respectively. We identified six positively selected genes that are mainly involved in stimulus responses, suggesting that environmental adaptation may have played an important role in the relatively recent divergence of these species. The similar K S distribution peaks at 1.0 observed for the paralogs in the two species indicate a common whole-genome duplication event. Our species delimitation analysis indicated that the C. taiwaniana complex consists of three distinct species, which correspond to the previously reported morphological differences. Discussion:Our study provides valuable genetic resources for Cycas species and guidance for the taxonomic treatment of the C. taiwaniana complex, as well as new insights into evolution of species within Cycas.

SUBMITTER: Wang XH

PROVIDER: S-EPMC6814181 | biostudies-literature | 2019 Oct

REPOSITORIES: biostudies-literature

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Transcriptome analysis of two radiated <i>Cycas</i> species and the subsequent species delimitation of the <i>Cycas taiwaniana</i> complex.

Wang Xin-Hui XH Wu Wei W Jian Shu-Guang SG

Applications in plant sciences 20191016 10

<h4>Premise</h4><i>Cycas</i> is an important gymnosperm genus, and the most diverse of all cycad genera. The <i>C. taiwaniana</i> complex of species are morphologically similar and difficult to distinguish due to a lack of genomic resources.<h4>Methods</h4>We characterized the transcriptomes of two closely related and endangered <i>Cycas</i> species endemic to Hainan, China: <i>C. hainanensis</i> and <i>C. changjiangensis</i>. Three single-copy nuclear genes in the <i>C. taiwaniana</i> complex w ...[more]

PMID: 31667020

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Project description:Delimitating species boundaries could be of critical importance when evaluating the species' evolving process and providing guidelines for conservation genetics. Here, species delimitation was carried out on three endemic and endangered Cycas species with resembling morphology and overlapped distribution range along the Red River (Yuanjiang) in China: Cycas diananensis Z. T. Guan et G. D. Tao, Cycas parvula S. L. Yang and Cycas multiovula D. Y. Wang. A total of 137 individuals from 15 populations were genotyped by using three chloroplastic (psbA-trnH, atpI-atpH, and trnL-rps4) and two single copy nuclear (RPB1 and SmHP) DNA sequences. Basing on the carefully morphological comparison and cladistic haplotype aggregation (CHA) analysis, we propose all the populations as one species, with the rest two incorporated into C. diannanensis. Genetic diversity and structure analysis of the conflated C. diannanensis revealed this species possessed a relative lower genetic diversity than estimates of other Cycas species. The higher genetic diversity among populations and relative lower genetic diversity within populations, as well as obvious genetic differentiation among populations inferred from chloroplastic DNA (cpDNA) suggested a recent genetic loss within this protected species. Additionally, a clear genetic structure of C. diannanensis corresponding with geography was detected based on cpDNA, dividing its population ranges into "Yuanjiang-Nanhun" basin and "Ejia-Jiepai" basin groups. Demographical history analyses based on combined cpDNA and one nuclear DNA (nDNA) SmHP both showed the population size of C. diannanensis began to decrease in Quaternary glaciation with no subsequent expansion, while another nDNA RPB1 revealed a more recent sudden expansion after long-term population size contraction, suggesting its probable bottleneck events in history. Our findings offer grounded views for clarifying species boundaries of C. diannanensis when determining the conservation objectives. For operational guidelines, the downstream populations which occupy high and peculiar haplotypes should be given prior in-situ conservation. In addition, ex-situ conservation and reintroduction measures for decades of generations are supplemented for improving the population size and genetic diversity of the endemic and endangered species.

Project description:Species delimitation in tree species is notoriously challenging due to shared polymorphisms among species. An integrative survey that considers multiple operational criteria is a possible solution, and we aimed to test it in a species complex of aspens in China. Genetic [four chloroplast DNA (cpDNA) fragments and 14 nuclear microsatellite loci (nSSR)] and morphological variations were collected for 76 populations and 53 populations, respectively, covering the major geographic distribution of the Populus davidiana-rotundifolia complex. Bayesian clustering, analysis of molecular variance (AMOVA), Principle Coordinate Analysis (PCoA), ecological niche modeling (ENM), and gene flow (migrants per generation), were employed to detect and test genetic clustering, morphological and habitat differentiation, and gene flow between/among putative species. The nSSR data and ENM suggested that there are two separately evolving meta-population lineages that correspond to P. davidiana (pd) and P. rotundifolia (pr). Furthermore, several lines of evidence supported a subdivision of P. davidiana into Northeastern (NEC) and Central-North (CNC) groups, yet they are still functioning as one species. CpDNA data revealed that five haplotype clades formed a pattern of [pdNEC, ((pdCNC, pr), (pdCNC, pr))], but most haplotypes are species-specific. Meanwhile, PCA based on morphology suggested a closer relationship between the CNC group (P. davidiana) and P. rontundifolia. Discrepancy of nSSR and ENM vs. cpDNA and morphology could have reflected a complex lineage divergence and convergence history. P. davidiana and P. rotundifolia can be regarded as a recently diverged species pair that experienced parapatric speciation due to ecological differentiation in the face of gene flow. Our findings highlight the importance of integrative surveys at population level, as we have undertaken, is an important approach to detect the boundary of a group of species that have experienced complex evolutionary history.

Dataset Information

Transcriptome analysis of two radiated Cycas species and the subsequent species delimitation of the Cycas taiwaniana complex.

Publications

Transcriptome analysis of two radiated <i>Cycas</i> species and the subsequent species delimitation of the <i>Cycas taiwaniana</i> complex.

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