Icelandic Birch Polyploids—The Case of a Perfect Fit in Genome Size

Abstract

Two birch species coexist in Iceland, dwarf birch Betula nana and tree birch B. pubescens. Both species are variable morphologically, which has been shown to be due to introgressive hybridization via interspecific hybrids. The aim of this study was to examine if the introgression could be related to genome size. We characterized 42 plants from Bifröst woodland morphologically and cytogenetically. The population consisted of diploid B. nana (38%), tetraploid B. pubescens (55%), and triploid hybrids (7%). Genome size was measured from 12 plants, using Feulgen DNA image densitometry (FDM) on spring leaf buds and flow cytometry (FCM) with dormant winter twigs. The use of winter twigs for FCM is novel. The average 1C-values for diploid, triploid, and tetraploid plants were 448, 666, and 882 Mbp, respectively. Monoploid genome sizes were found to be statistically constant among ploidy levels. This stability is in contrast to the different taxonomic positions of the di-and tetraploids and also contrasts with the frequent occurrence of genome downsizing in polyploids.

Genome sequence of dwarf birch (Betula nana) and cross‐species RAD markers

“…unreplicated haploid genome size) values of 453 and 462 Mbp, and three plants analysed using Feulgen DNA Image Densitometry had 1C values of 441, 432 and 451 Mbp (Anamthawat‐Jónsson et al . ).…”

Genesis of the karelian birch. an ecogenetic hypothesis

“…Наши предположения о присутствии в геноме березы пушистой аллельных вариантов (генома) березы пови-слой [9] в дальнейшем были подтверждены результатами молекулярно-генетических исследований [3, 46,62,99].…”

“…Что касается источника второго генома, составля-ющего тетраплоид березы пушистой, то здесь мнения расходятся. Одни авторы называют березу карликовую [2, 46,99], другие -березу приземистую [98], а тре-тьи -такой диплоид, который, возможно, уже не суще-ствует в природе [62], поскольку специфичные для бере-зы пушистой изоферменты, жирные кислоты и эфирные масла не обнаружены пока ни у одного из исследованных диплоидов.…”

Hybridisation, Introgression and Phylogeography of Icelandic Birch

“…2), even though birch is an ecologically and economically important plant. Research studies in this category are very diverse: from mapping the demographic variation of dwarf birch B. nana (Ejankowski 2010) and developing molecular markers for use in the breeding of tree-birch species such as B. pendula and B. alnoides (Guo et al 2008;Jiang et al 2011) to resolving phylogenetic relationships among Betula species using genome-wide markers, nuclear genes or DNA barcodes (Li et al 2007;Schenk et al 2008;Crautlein et al 2011) and answering questions about the origin, hybridisation, introgression and phylogeography of a number of Betula species using molecular markers, botanical and statistical approaches, and macro-and microfossil evidence (Nagamitsu et al 2006;Maliouchenko et al 2007;Thórsson et al 2007;Truong et al 2007;Karlsdóttir et al 2009;Anamthawat-Jónsson et al 2010;Thórsson et al 2010;Tsuda & Ide 2010). It is indeed our studies of Betula species from Iceland that have made a major contribution to a better understanding of birch hybridisation, introgression and phylogeography in general.…”

“…My own work, together with that of my research group during the past twenty years, has shown that introgressive hybridisation (introgression and gene flow) is probably the most significant drive towards the present-day variability in Icelandic birch. The second objective of this paper is therefore to review all evidence supporting hybridisation and introgression in Betula, notably interspecific hybrids from crossing experiments Tómasson 1990 and, a qualitative and quantitative assessment of morphological variation of birch in natural woodlands (Thórsson et al 2001 and, triploid birch hybrids (Anamthawat-Jónsson & Thórsson 2003;Anamthawat-Jónsson et al 2010) and birch palynology and Holocene hybridisation (Karlsdóttir et al 2007(Karlsdóttir et al , 2008(Karlsdóttir et al and 2009). All of this evidence indicates that Iceland could be considered as a birch hybrid zone, harbouring genetic variation which is likely to be advantageous in the arctic and subarctic environments.…”