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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.

SUBMITTER: Matthews A

PROVIDER: S-EPMC4571729 | biostudies-literature | 2015 Jul

REPOSITORIES: biostudies-literature

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250 years of hybridization between two biennial herb species without speciation.

Matthews Andrew A Emelianova Katie K Hatimy Abubakar A AA Chester Michael M Pellicer Jaume J Ahmad Khawaja Shafique KS Guignard Maité S MS Rouhan Germinal G Soltis Douglas E DE Soltis Pamela S PS Leitch Ilia J IJ Leitch Andrew R AR Mavrodiev Evgeny V EV Buggs Richard J A RJ

AoB PLANTS 20150717

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 fertil ...[more]

PMID: 26187604

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Project description:The study of mechanisms that generate new species is considered fundamental for broad areas of ecology and evolution. Speciation is a continuous process in which reproductive isolation is established, and it is of fundamental importance to understand the origins of the adaptations that contribute to this process. Hybrid zones are considered natural laboratories for the study of speciation and represent ideal systems for such studies. Here, we investigated genomic differentiation between hybridizing Neotropical species Pitcairnia staminea (G. Lodd.) and P. albiflos (Herb.). Using thousands of SNPs genotyped through RAD-seq, we estimate effective population sizes, interspecific gene flow, as well as time of divergence between these two sister species and identify candidate genomic regions for positive selection that may be related to reproductive isolation. We selected different scenarios of speciation and tested them by using approximate Bayesian computation (ABC); we found evidence of divergence with gradual reduction in gene flow between these species over time, compatible with the hypothesis of speciation with gene flow between these Pitcairnia species. The parameter estimates obtained through ABC suggested that the effective population size of P. albiflos was around three times larger than that of P. staminea. Our divergence date estimates showed that these two species diverged during the Pliocene (4.7 Mya; CI = 1.3-8.5 Mya), which has likely allowed this species to accumulate genome-wide differences. We also detected a total of 17 of 4165 loci which showed signatures of selection with high genetic differentiation (F ST > 0.85), 12 of these loci were annotated in de novo assembled transcriptomes of both species, and 4 candidate genes were identified to be putatively involved in reproductive isolation. These four candidate genes were previously associated with the function of pollen development, pollen tube germination and orientation, abiotic stress, and flower scent in plants, suggesting an interplay between pre- and postpollination barriers in the evolution of reproductive isolation between such species.

Dataset Information

250 years of hybridization between two biennial herb species without speciation.

Publications

250 years of hybridization between two biennial herb species without speciation.

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