Species Delimitation and Lineage Separation History of a Species Complex of Aspens in China

Abstract

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.

Allopatric divergence and hybridization withinCupressus chengiana(Cupressaceae), a threatened conifer in the northern Hengduan Mountains of western China

“…To further examine the patterns of distribution shifts within C. chengiana , we also used ENM to predict potential distributions during the Last Interglacial (LIG, ~120,000–140,000 years ago), the Last Glacial Maximum (LGM, about 22,000 years ago) and the future (2050, average for 2041–2060) for each group. For the period of the LGM, layers of four models available at the WorldClim database were downloaded to generate average‐over‐pixel bioclimatic variables following Zheng et al (2017). Future climate data were available from the Fifth Phase of the Coupled Model Intercomparison Project (CMIP5), while the climate data for the LIG were downloaded from the WorldClim database (source: Otto‐Bliesner, Marshall, Overpeck, Miller, & Hu, 2006).…”

An integrating study of genetic diversity and ecological niche modelling in Salvia aristata (Lamiaceae)

“…Identifying the accurate boundaries of a species is critical to have a better perspective of any biological studies. Therefore, species delimitation is a subject of extensive part of studies in the framework of biology (Rissler and Apodaca 2007, Rivera et al 2011, Zheng et al 2017. However, defining the criterion which could address the boundaries of species is different and the place of debates (Levin 2000).…”

A snapshot of progenitor-derivative speciation in action inIberodes(Boraginaceae)

“…Indeed, the projection of distribution models to past climatic periods during the Quaternary revealed a similar or greater degree of geographic overlap between the potential ranges of I. linifolia and I. kuzinskyana (Fig. 4), which makes allopatry unlikely (Zheng et al , 2017). Peripheral populations of the widespread I. linifolia close to the coast of Portugal are the most closely related and possible living progenitor of coastland species ( I. kuzinskyana and I. littoralis; Fig.…”

“…In the last decade, new genomic, phylogenetic, and ecological tools have made non-allopatric modes of speciation increasingly amenable to study, allowing us to explore with statistical rigor a wider range of speciation scenarios (e.g. Savolainen et al , 2006; Chozas et al , 2017; Zheng et al , 2017). In particular, there are some critical points of evidence that would support a parapatric scenario: (1) phylogenetic relationships usually reflect a progenitor-derivative (budding) pattern in which the most widely distributed species is the living progenitor of the most restricted one; (2) the absence of any physical barrier to gene-flow in both present and past times, i.e.…”