title: Unidirectional diploid-tetraploid introgression among British birch trees with shifting ranges shown by restriction site-associated markers.
abstract: Hybridization may lead to introgression of genes among species. Introgression may be bidirectional or unidirectional, depending on factors such as the demography of the hybridizing species, or the nature of reproductive barriers between them. Previous microsatellite studies suggested bidirectional introgression between diploid Betula nana (dwarf birch) and tetraploid B. pubescens (downy birch) and also between B. pubescens and diploid B. pendula (silver birch) in Britain. Here, we analyse introgression among these species using 51 237 variants in restriction site-associated (RAD) markers in 194 individuals, called with allele dosages in the tetraploids. In contrast to the microsatellite study, we found unidirectional introgression into B. pubescens from both of the diploid species. This pattern fits better with the expected nature of the reproductive barrier between diploids and tetraploids. As in the microsatellite study, introgression into B. pubescens showed clear clines with increasing introgression from B. nana in the north and from B. pendula in the south. Unlike B. pendula alleles, introgression of B. nana alleles was found far from the current area of sympatry or allopatry between B. nana and B. pubescens. This pattern fits a shifting zone of hybridization due to Holocene reduction in the range of B. nana and expansion in the range of B. pubescens.
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London, E1 4NS, UK.
authors.forename: Jasmin
authors.initials: J
authors.lastname: Zohren
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London, E1 4NS, UK.
authors.forename: Nian
authors.initials: N
authors.lastname: Wang
authors.affiliation: QIAGEN Aarhus A/S, Silkeborgvej 2, Prismet, Aarhus C, 8000, Denmark.
authors.forename: Igor
authors.initials: I
authors.lastname: Kardailsky
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London, E1 4NS, UK.
authors.forename: James S
authors.initials: JS
authors.lastname: Borrell
authors.affiliation: QIAGEN Aarhus A/S, Silkeborgvej 2, Prismet, Aarhus C, 8000, Denmark.
authors.forename: Anika
authors.initials: A
authors.lastname: Joecker
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London, E1 4NS, UK.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Nichols
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London, E1 4NS, UK.
authors.forename: Richard J A
authors.initials: RJ
authors.lastname: Buggs
mesh_terms: D000483:Alleles; D029662:Betula / Q000235:genetics*; D005075:Biological Evolution; D002874:Chromosome Mapping; D018744:DNA, Plant / Q000235:genetics; D004171:Diploidy; D005819:Genetic Markers; D005828:Genetics, Population; D005838:Genotype; D006824:Hybridization, Genetic; D018895:Microsatellite Repeats; D017422:Sequence Analysis, DNA; D057891:Tetraploidy; D006113:United Kingdom
chemical_list: D018744:DNA, Plant; D005819:Genetic Markers
keywords: climate change; genotyping; hybridization; introgression; polyploidy