Resolving phylogeny and polyploid parentage using genus-wide genome-wide sequence data from birch trees.

Area of Science:

• Botany
• Evolutionary Biology
• Genomics

Background:

• Plant genera like Betula exhibit complex reticulate evolution due to hybridization and polyploidization, making traditional tree-based phylogenies insufficient.
• The genus Betula, comprising ecologically significant tree species, exemplifies these phylogenetic challenges.

Purpose of the Study:

• To reconstruct the evolutionary history of the Betula genus, accurately depicting the reticulate origins of its polyploid species.
• To propose a revised classification for Betula based on phylogenetic findings.

Main Methods:

• Generated genome-wide sequence reads from 27 diploid and 36 polyploid Betula taxa using restriction site associated DNA (RAD) sequencing.
• Reconstructed phylogenetic relationships using supermatrix and species tree methods, identifying diploid relatives of polyploids by read mapping.
• Assembled contigs from putative sub-genomes of allopolyploids to build phylogenies including polyploid sub-genomes as separate tips.

Main Results:

• Developed a robust phylogenetic hypothesis for Betula, revealing the complex reticulate origins of most polyploid taxa.
• Identified two well-supported clades within the genus Betula.
• Observed a correlation between the identified clades and distinct seed-wing morphologies.

Conclusions:

• The study provides a comprehensive phylogenetic framework for Betula, accommodating its reticulate evolutionary history.
• Based on phylogenetic and morphological evidence, a split of the genus Betula into two subgenera is proposed.