Evidence of hybridisation between Betula pubescens and B. nana in Iceland during the early Holocene

Karlsdóttir, Lilja; Hallsdóttir, Margrét; Thórsson, Ægir Th.; Anamthawat‐Jónsson, Kesara

doi:10.1016/j.revpalbo.2009.04.001

Cited by 23 publications

(16 citation statements)

References 34 publications

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“…High proportion of non-triporate pollen therefore indicates the presence of hybrids and, in turn, the presence of both parent species in the region. The proportion of non-triporate pollen during this period ranges between 2% and 9% ( Figure 6), which indicates hybridization already taking place during the early Holocene, similar to what has been observed in other early-Holocene pollen records from Iceland (Karlsdóttir, 2014;Karlsdóttir et al, 2009Karlsdóttir et al, , 2012.…”

Section: Environmental Instability Local Increase In Juniperus Commusupporting

confidence: 84%

Life on the periphery is tough: Vegetation in Northwest Iceland and its responses to early-Holocene warmth and later climate fluctuations

2015

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Long-and short-term climate variations in the North Atlantic have been of sufficient magnitude to leave a discernible mark on the history of vegetation and landscape stability in Iceland during the Holocene. A reconstruction of early-and mid-Holocene vegetation around Lake Kagaðarhóll, Northwest Iceland, examines how climate fluctuations have affected the terrestrial ecosystem. A thorough reconstruction has been made using pollen and plant macrofossil analyses combined with proxies for organic and inorganic matter. The record shows the development from a period of pioneer vegetation towards a woodland ecosystem. The deposition of the Saksunarvatn tephra at c. 10,300 cal. yr BP caused a 100-year period of instability, followed by a gradual trend of stabilization over several centuries while material left behind by retreating glaciers and tephra was being contained by expanding and developing vegetation. Early-Holocene warmth is indicated by high pollen production of Juniperus communis around the lake by c. 10,100 cal. yr BP and birch woodland being established around the lake by c. 9200 cal. yr BP, much earlier than previously believed for this locale. Cooling climate between c. 8700 and 8200 cal. yr BP halted woodland development, with reduced plant reproduction likely caused by cold spring and summer temperatures. Woodlands became re-established from c. 7900 cal. yr BP before entering a decline from c. 6000 cal. yr BP, with harsher environmental conditions apparent after c. 4200 cal. yr BP. The Kagaðarhóll record compares favourably with other palaeoclimatic data from the North Atlantic, demonstrating the potential of pollen and macrofossil data for reconstructions of environmental change in Iceland and as an indicator of climate variability in the North Atlantic during the Holocene.

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Section: Environmental Instability Local Increase In Juniperus Commusupporting

confidence: 84%

Life on the periphery is tough: Vegetation in Northwest Iceland and its responses to early-Holocene warmth and later climate fluctuations

2015

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“…Our hypothesis is that such a cline exists and is the result of introgression between B. nana and other Betula species as a hybrid zone between them moved northwards through Britain due to global warming after the last glacial maximum (Huntley & Birks ; Caseldine ; Buggs ; Karlsdóttir et al . ). RAD sequencing has proved to be informative in the assessing hybridization among Heliconiu s species (Dasmahapatra et al .…”

Section: Discussionmentioning

confidence: 97%

“…) as the ranges of Betula species have shifted due to climate change (Huntley & Birks ; Caseldine ; Karlsdóttir et al . ).…”

Section: Introductionmentioning

confidence: 97%

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

Wang

Thomson

Bodles³

et al. 2012

Molecular Ecology

138

111

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New sequencing technologies allow development of genome-wide markers for any genus of ecological interest, including plant genera such as Betula (birch) that have previously proved difficult to study due to widespread polyploidy and hybridization. We present a de novo reference genome sequence assembly, from 66× short read coverage, of Betula nana (dwarf birch) - a diploid that is the keystone woody species of subarctic scrub communities but of conservation concern in Britain. We also present 100 bp PstI RAD markers for B. nana and closely related Betula tree species. Assembly of RAD markers in 15 individuals by alignment to the reference B. nana genome yielded 44-86k RAD loci per individual, whereas de novo RAD assembly yielded 64-121k loci per individual. Of the loci assembled by the de novo method, 3k homologous loci were found in all 15 individuals studied, and 35k in 10 or more individuals. Matching of RAD loci to RAD locus catalogues from the B. nana individual used for the reference genome showed similar numbers of matches from both methods of RAD locus assembly but indicated that the de novo RAD assembly method may overassemble some paralogous loci. In 12 individuals hetero-specific to B. nana 37-47k RAD loci matched a catalogue of RAD loci from the B. nana individual used for the reference genome, whereas 44-60k RAD loci aligned to the B. nana reference genome itself. We present a preliminary study of allele sharing among species, demonstrating the utility of the data for introgression studies and for the identification of species-specific alleles.

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“…When considering the haplotypes unique to Iceland, it is noteworthy that five of the six haplotypes that were found in more than one individual are shared by plants of different ploidy groups, suggesting that introgressive hybridization took place after birch colonization in Iceland. A recent study of birch pollen from early Holocene sediments (Karlsdóttir et al. , 2009) has indeed shown that hybridization between these two birch species occurred early on in the birch colonization and expansion periods.…”

Section: Discussionmentioning

confidence: 97%

Introgression and phylogeography ofBetula nana(diploid),B. pubescens(tetraploid) and their triploid hybrids in Iceland inferred from cpDNA haplotype variation

Thórsson¹,

Pálsson²,

Lascoux³

et al. 2010

Journal of Biogeography

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The genus Betula is distributed throughout the northern temperate regions. In most of Europe there are two species of tree birch (Atkinson, 1992): silver birch (Betula pendula Roth., diploid 2n = 2x = 28) and downy birch (Betula pubescens Ehrh., tetraploid 2n = 4x = 56). There is considerable overlap in the distribution of these two species, but silver birch extends further south into the Balkans, while downy birch is found in northern Europe, including Fennoscandia (the northern part of Scandinavia and Finland). Another birch species found in Europe is dwarf birch (Betula nana L., diploid 2n = 2x = 28) (de Groot et al., 1997). It is a circumpolar species with a distribution in both Alpine and Arctic regions that overlaps with the range of tree birch species, especially with downy birch in northern Scandinavia and Russia. Only dwarf birch ABSTRACT Aim The objective was to find direct genetic evidence supporting introgressive hybridization between tetraploid tree birch (Betula pubescens) and diploid dwarf birch (B. nana), via triploid hybrids, and to investigate an association between the introgression and phylogeographical distribution of Icelandic birch.Location Samples were collected from 463 trees in 12 woodlands in Iceland and eight locations in Norway, Sweden, Scotland and Greenland.Methods Ploidy status of individual trees was determined by chromosome counting. Variation in the chloroplast genome was assessed using polymerase chain reaction-restriction fragment length polymorphism. The geographical distribution of the haplotypes was mapped. The haplotype variation and introgression ratios (IG) were analysed statistically.Results Thirteen haplotypes were identified among Icelandic samples. The most common haplotype (T, 49% occurrence) was present in all ploidy groups and in all woodlands. All common haplotypes were shared between the triploid group and the parental species, indicating introgressive hybridization. This was supported by the statistical analysis of IG indices and the variation components. Considerable differences existed among samples, shaped by isolation by distance and local introgression. An east-west phylogeographical distribution in Iceland was observed.Main conclusions Despite extensive introgression across species and ploidy levels, a biogeographical pattern has been observed, and this may indicate different population histories or multiple origins of Icelandic birch. The chloroplast haplotype diversity found in Iceland resembles that found in birch populations from northern Scandinavia.

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Evidence of hybridisation between Betula pubescens and B. nana in Iceland during the early Holocene

Cited by 23 publications

References 34 publications

Life on the periphery is tough: Vegetation in Northwest Iceland and its responses to early-Holocene warmth and later climate fluctuations

Life on the periphery is tough: Vegetation in Northwest Iceland and its responses to early-Holocene warmth and later climate fluctuations

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

Introgression and phylogeography ofBetula nana(diploid),B. pubescens(tetraploid) and their triploid hybrids in Iceland inferred from cpDNA haplotype variation

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