Hybridisation and phylogenomics of Betula L. (Betulaceae).
Abstract
Hybridisation and polyploidy are important in the evolution of species. The genus
Betula L. is an ideal model to study these processes as species of this genus hybridise
frequently and polyploid species are common. In this thesis, I investigated the
hybridisation of three Betula species in Britain; the phylogenetic relationships and
genome size of all known Betula species, and conducted phylogenomic analysis of
diploid Betula species.
A cline of introgression of microsatellite marker alleles from B. nana was found
extending into B. pubescens populations far to the south of the current B. nana range in
Britain. We suggest that this genetic pattern is a footprint of a historical decline and/or
northwards shift in the range of B. nana populations due to climate warming in the
Holocene.
The Atkinson Discriminant Function (ADF) is a leaf-morphology metric to distinguish
between B. pubescens and B. pendula. We test it on 944 trees sampled across Britain
against species‟ discriminations made using 12 microsatellite loci and found that the
accuracy of the ADF can be raised to 97.5% by using an ADF of -2 rather than zero as
the boundary line between the species.
The taxonomy of the genus Betula is debated and a new classification has been
proposed in a recent monograph. We evaluated it using ITS and restriction site
associated DNA sequencing (RADSeq). The result based on ITS largely agrees with
species classification in the recent monograph but with uncertainties. Phylogenomic
analysis of 587 RAD loci for Betula diploid species using coalescence-based methods,
a concatenation method and binary presence/absence of RAD loci produced wellresolved
trees with similar topology. Based on these analyses, we propose a new
classification of Betula into four subgenera and seven sections. Further research is
needed to infer the parental origins of polyploid species within Betula.
Authors
Wang, NianCollections
- Theses [3834]