Search

Carpinus (Betulaceae) has approximately 52 species distributed in the Northern Hemisphere, with many species of Carpinus found in China. However, the species boundaries and phylogenetic relationships remain poorly understood. This study reported ITS sequences for 225 individuals of 33 Carpinus species, mainly from China. We also included eight Ostrya species in our analyses, the closely related sister group of Carpinus. We aimed to delimit these species based on ITS sequences and clarify their phylogenetic relationships by constructing tree-like topology and networks at population level. We found that only 17 of 33 species could be delimited from the closely related ones based on species-specific mutations in ITS sequence variation, including all species of sect. Distegocarpus , and sect. Carpinus subsect. Carpinus. Carpinus subsect. Carpinus contained two endangered species, although one seemed to be a recently originated allopolyploid species with genetic additivity from two likely parents in the ITS sequence variation. Sixteen species of sect. Carpinus subsect. Polyneurae were classified into three species complexes, in each of which two or more could be not distinguished from each other. The closely related species of these complexes may still diverge at the early stage without genetic distinction in the nuclear ITS sequences because of too short of divergence time and frequent gene flow. Otherwise, some species may be established based on the intraspecific variations without genetic bases for an independently evolving unit. [ABSTRACT FROM AUTHOR]

Background and Aims Genetic drift due to geographical isolation, gene flow and mutation rates together make it difficult to determine the evolutionary relationships of present-day species. In this study, population genetic data were used to model and decipher interspecific relationships, speciation patterns and gene flow between three species of spruce with similar morphology, Picea wilsonii, P. neoveitchii and P. morrisonicola. Picea wilsonii and P. neoveitchii occur from central to north-west China, where they have overlapping distributions. Picea morrisonicola, however, is restricted solely to the island of Taiwan and is isolated from the other two species by a long distance. Methods Sequence variations were examined in 18 DNA fragments for 22 populations, including three fragments from the chloroplast (cp) genome, two from the mitochondrial (mt) genome and 13 from the nuclear genome. Key Results In both the cpDNA and the mtDNA, P. morrisonicola accumulated more species-specific mutations than the other two species. However, most nuclear haplotypes of P. morrisonicola were shared by P. wilsonii, or derived from the dominant haplotypes found in that species. Modelling of population genetic data supported the hypothesis that P. morrisonicola derived from P. wilsonii within the more recent past, most probably indicating progenitor–derivative speciation with a distinct bottleneck, although further gene flow from the progenitor to the derivative continued. In addition, the occurrence was detected of an obvious mtDNA introgression from P. neoveitchii to P. wilsonii despite their early divergence. Conclusions The extent of mutation, introgression and lineage sorting taking place during interspecific divergence and demographic changes in the three species had varied greatly between the three genomes. The findings highlight the complex evolutionary histories of these three Asian spruce species. [ABSTRACT FROM AUTHOR]

Population genetics data based on multiple nuclear loci provide invaluable information to understand demographic, selective, and divergence histories of the current species. We studied nucleotide variation at 13 nuclear loci in 53 populations distributed among four closely related, but morphologically distinct juniper species of the Qinghai-Tibetan Plateau (QTP). We used a novel approach combining Approximate Bayesian Computation and a recently developed neutrality test based on the maximum frequency of derived mutations to examine the demographic and selective histories of individual species, and isolation-with-migration analyses to study the joint history of the species and detect gene flow between them. We found that (1) the four species, which diverged in response to the extensive QTP uplifts, have different demographic histories; (2) two loci, Pgi and CC0822, depart significantly from neutrality in one species and Pgi, is also marginally significant in another; and (3) shared polymorphisms are common, indicating both incomplete lineage sorting and gene flow after species divergence. In addition, the detected unidirectional gene flow provides indirect support for the theoretical prediction that introgression should mostly take place from local to invading species. Our results, together with previous studies, underscore complex evolutionary histories of plant diversification in the biodiversity-hotspot QTP. [ABSTRACT FROM AUTHOR]