Population structure of Betula albosinensis and Betula platyphylla: evidence for hybridization and a cryptic lineage

Abstract

Background and AimsDifferences in local abundance and ploidy level are predicted to impact the direction of introgression between species. Here, we tested these hypotheses on populations of Betula albosinensis (red birch) and Betula platyphylla (white birch) which were thought to differ in ploidy level, the former being tetraploid and the latter diploid.MethodsWe sampled 391 birch individuals from nine localities in China, and classified them into species based on leaf morphology. Twelve nuclear microsatellite markers were genotyped in each sample, and analysed using principal coordinates analysis and STRUCTURE software. We compared the effects of two different methods of scoring polyploid genotypes on population genetic analyses. We analysed the effect of ploidy, local species abundance and latitude on levels of introgression between the species.Key ResultsLeaf morphology divided our samples into red and white birch, but genetic analyses unexpectedly revealed two groups within red birch, one of which was tetraploid, as expected, but the other of which appeared to have diploid microsatellite genotypes. Five individuals were identified as early-generation hybrids or backcrosses between white birch and red birch and five were identified between red birch and ‘diploid’ red birch. Cline analysis showed that levels of admixture were not significantly correlated with latitude. Estimated genetic differentiation among species was not significantly different between determined tetraploid and undetermined tetraploid genotypes.ConclusionsLimited hybridization and gene flow have occurred between red birch and white birch. Relative species abundance and ploidy level do not impact the direction of introgression between them, as genetic admixture is roughly symmetrical. We unexpectedly found populations of apparently diploid red birch and this taxon may be a progenitor of allotetraploid red birch populations. Incomplete lineage sorting may explain patterns of genetic admixture between apparently diploid and allotetraploid red birch.

A basic/helix–loop–helix transcription factor controls leaf shape by regulating auxin signaling in apple

“…A total of 1535 leaves were scanned using a Hewlett‐Packard printer (LaserJet Pro MFP M128fn; Hewlett‐Packard, Palo Alto, CA, USA) with a resolution of 600 dpi. Twelve landmarks were selected from each scanned leaf as previously described (Viscosi et al ., 2009; Y. N. Hu et al ., 2019), consisting of: the junction between the petiole and the leaf blade; the first serration on the right‐hand side of the leaf; the right‐hand point of one‐fifth of the leaf from the lower side; the right‐hand point of the widest part of leaf; the right‐hand point of three‐fifths of the leaf from the lower side; the right‐hand point of four‐fifths of each leaf from the lower side; the leaf tip; the left‐hand point of four‐fifths of the leaf from the lower side; the left‐hand point of three‐fifths of the leaf from the lower side; the left‐hand point of the widest part of the leaf; the left‐hand point of one‐fifth of the leaf from the lower side; and the first serration on the left‐hand side of the leaf. The x and y coordinates of each landmark were recorded on digitized leaves using the program ImageJ (Abràmoff et al ., 2004).…”

Molecular and morphological analyses clarify species delimitation and reveal a newBetulaspecies in sectionCostatae

“…Leaves were scanned individually using a Hewlett-Packard printer (LaserJet Pro MFP M128fn) with a resolution of 600 dpi. Thirteen landmarks were selected from each scanned leaf according to the protocols of (Liu et al, 2018; Hu et al, 2019). The 13 landmarks were converted to a configuration of 26 cartesian coordinates using ImageJ (Abràmoff et al, 2004).…”

“…utilis was not recorded in Ashburner and McAllister’s monograph (Ashburner & McAllister, 2016) (Table 1). Recently, a ‘diploid’ B. albosinensis has been discovered from the Qinling Mountains in central China (Hu et al, 2019). A phylogenetic tree based on the internal transcribed spacer (ITS) region indicated a close relationship between the ‘diploid’ B. albosinensis, B. ashburneri and B. costata (Hu et al, 2019).…”

Population genetic structures of two ecologically distinct species Betula platyphylla and B. ermanii inferred based on nuclear and chloroplast DNA markers

“…In genetic structure analysis of total samples, the genotypes of the B. platyphylla individuals were duplicated to show tetraploid-like genotypes. As ambiguous locus was found for a few individuals of B. ermani, we created another dataset of B. ermanii for STRUCTURE analysis according Hu et al (2019). In the new dataset, we used missing data (−9) to replace the repeated genotypes when a tetraploid has two or three alleles.…”