title: 250 years of hybridization between two biennial herb species without speciation.
abstract: Hybridization between plant species can generate novel morphological diversity and lead to speciation at homoploid or polyploid levels. Hybrids between biennial herbs Tragopogon pratensis and T. porrifolius have been studied in experimental and natural populations for over 250 years. Here we examine their current status in natural populations in southeast England. All hybrids found were diploid; they tended to grow taller and with more buds than their parental species; many showed partial fertility; a few showed evidence of backcrossing. However, we found no evidence to suggest that the hybrids are establishing as a new species, nor can we find literature documenting speciation of these hybrids elsewhere. This lack of speciation despite at least 250 years of hybridization contrasts with the fact that both parental species have formed new allopolyploid species through hybridization with another diploid, T. dubius. Understanding why hybrids often do not speciate, despite repeated opportunities, would enhance our understanding of both the evolutionary process and risk assessments of invasive species.
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK Present address: Division of Ecology and Evolution, Imperial College London, Silwood Park Campus, Ascot, UK.
authors.forename: Andrew
authors.initials: A
authors.lastname: Matthews
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK.
authors.forename: Katie
authors.initials: K
authors.lastname: Emelianova
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK.
authors.forename: Abubakar A
authors.initials: AA
authors.lastname: Hatimy
authors.affiliation: Department of Biology, University of Florida, Gainesville, FL 32611, USA Department of Plant Science, University of Oxford, South Parks Road, Oxford OX1 3RB, UK.
authors.forename: Michael
authors.initials: M
authors.lastname: Chester
authors.affiliation: Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3DS, UK.
authors.forename: Jaume
authors.initials: J
authors.lastname: Pellicer
authors.affiliation: Lab of Plant Taxonomy, Department of Botany, University of Agriculture, Faisalabad 38040, Pakistan.
authors.forename: Khawaja Shafique
authors.initials: KS
authors.lastname: Ahmad
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK.
authors.forename: Maité S
authors.initials: MS
authors.lastname: Guignard
authors.affiliation: Museum national d'Histoire naturelle, UMR CNRS 7205, Herbier National, CP3916 rue Buffon, F-75231 Paris, France.
authors.forename: Germinal
authors.initials: G
authors.lastname: Rouhan
authors.affiliation: Department of Biology, University of Florida, Gainesville, FL 32611, USA Florida Museum of Natural History, University of Florida, Gainesville, FL 32611, USA.
authors.forename: Douglas E
authors.initials: DE
authors.lastname: Soltis
authors.affiliation: Florida Museum of Natural History, University of Florida, Gainesville, FL 32611, USA.
authors.forename: Pamela S
authors.initials: PS
authors.lastname: Soltis
authors.affiliation: Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3DS, UK.
authors.forename: Ilia J
authors.initials: IJ
authors.lastname: Leitch
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Leitch
authors.affiliation: Florida Museum of Natural History, University of Florida, Gainesville, FL 32611, USA evgeny@ufl.edu r.buggs@qmul.ac.uk.
authors.forename: Evgeny V
authors.initials: EV
authors.lastname: Mavrodiev
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK evgeny@ufl.edu r.buggs@qmul.ac.uk.
authors.forename: Richard J A
authors.initials: RJ
authors.lastname: Buggs
keywords: Homoploid; Tragopogon; hybridization; invasive; speciation