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Natural hybridization and asymmetric introgression at the distribution margin of two Buddleja species with a large overlap.

ABSTRACT: BACKGROUND:Natural hybridization in plants is universal and plays an important role in evolution. Based on morphology it has been presumed that hybridization occurred in the genus Buddleja, though genetic studies confirming this assumption have not been conducted to date. The two species B. crispa and B. officinalis overlap in their distributions over a wide range in South-West China, and we aimed to provide genetic evidence for ongoing hybridization in this study. RESULTS:We investigated the occurrence of hybrids between the two species at the southern-most edge of the distribution of B. crispa using five nuclear loci and pollination experiments. The genetic data suggest substantial differentiation between the two species as species-specific alleles are separated by at least 7-28 mutations. The natural hybrids found were nearly all F1s (21 of 23), but backcrosses were detected, and some individuals, morphologically indistinguishable from the parental species, showed introgression. Pollen viability test shows that the percentage of viable pollen grains was 50?±?4% for B. crispa, and 81?±?2% for B. officinalis. This difference is highly significant (t?=?7.382, p?

SUBMITTER: Liao RL

PROVIDER: S-EPMC4470074 | biostudies-literature | 2015 Jun

REPOSITORIES: biostudies-literature

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Natural hybridization and asymmetric introgression at the distribution margin of two Buddleja species with a large overlap.

Liao Rong-Li RL Ma Yong-Peng YP Gong Wei-Chang WC Chen Gao G Sun Wei-Bang WB Zhou Ren-Chao RC Marczewski Tobias T

BMC plant biology 20150618

<h4>Background</h4>Natural hybridization in plants is universal and plays an important role in evolution. Based on morphology it has been presumed that hybridization occurred in the genus Buddleja, though genetic studies confirming this assumption have not been conducted to date. The two species B. crispa and B. officinalis overlap in their distributions over a wide range in South-West China, and we aimed to provide genetic evidence for ongoing hybridization in this study.<h4>Results</h4>We inve ...[more]

PMID: 26081944

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Project description:BackgroundAnalysis of interspecific gene flow is crucial for the understanding of speciation processes and maintenance of species integrity. Oaks (genus Quercus, Fagaceae) are among the model species for the study of hybridization. Natural co-occurrence of four closely related oak species is a very rare case in the temperate forests of Europe. We used both morphological characters and genetic markers to characterize hybridization in a natural community situated in west-central Romania and which consists of Quercus robur, Q. petraea, Q. pubescens, and Q. frainetto, respectively.ResultsOn the basis of pubescence and leaf morphological characters ~94% of the sampled individuals were assigned to pure species. Only 16 (approximately 6%) individual trees exhibited intermediate morphologies or a combination of characters of different species. Four chloroplast DNA haplotypes were identified in the study area. The distribution of haplotypes within the white oak complex showed substantial differences among species. However, the most common haplotypes were present in all four species. Furthermore, based on a set of 7 isozyme and 6 microsatellite markers and using a Bayesian admixture analysis without any a priori information on morphology we found that four genetic clusters best fit the data. There was a very good correspondence of each species with one of the inferred genetic clusters. The estimated introgression level varied markedly between pairs of species ranging from 1.7% between Q. robur and Q. frainetto to 16.2% between Q. pubescens and Q. frainetto. Only nine individuals (3.4%) appeared to be first-generation hybrids.ConclusionOur data indicate that natural hybridization has occurred at relatively low rates. The different levels of gene flow among species might be explained by differences in flowering time and spatial position within the stand. In addition, a partial congruence between phenotypically and genetically intermediate individuals was found, suggesting that intermediate appearance does not necessarily mean hybridization. However, it appears that natural hybridization did not seriously affect the species identity in this area of sympatry.

Dataset Information

Natural hybridization and asymmetric introgression at the distribution margin of two Buddleja species with a large overlap.

Publications

Natural hybridization and asymmetric introgression at the distribution margin of two Buddleja species with a large overlap.

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