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University of Lund

1. Sawangproh, Weerachon. Gene transfer by interspecific hybridization in bryophytes.

Degree: 2019, University of Lund

The role of hybridization in evolution has been debated for more than a century regarding bryophytes (mosses, liverworts, and hornworts) as well as most other organisms. Bryophytes have haplodiplontic life cycles with a dominant haploid generation. Hybridization in bryophytes involves fusion of gametes produced by haploid parental gametophytes of different species. The hybrid is thus the short-lived diploid sporophytes, which soon undergoes meiosis prior to forming a large amount of haploid recombinant spores. In this study, two moss species (Homalothecium lutescens and H. sericeum) and three subspecies of liverwort Marchantia polymorpha were investigated for evidence of gene transfer by hybridization.Firstly, we compared the morphology of gametophytes and sporophytes from allopatric and sympatric populations of H. lutescens and H. sericeum. Secondly, we used species-specific SNP markers to estimate the degree of genetic mixing in three generations (i.e., haploid maternal gametophytes, diploid sporophytes, and haploid sporelings) in samples from sympatric populations of H. lutescens and H. sericeum. Thirdly, we assessed fitness traits in relation to the degree of genetic admixture in sporophytes of H. lutescens and H. sericeum, including non-admixed, mildly and strongly admixed genotypes. Finally, we investigated the genome-wide scale phylogenetic relationship between the three subspecies of M. polymorpha to test the hypothesis that subsp. ruderalis has originated as a homoploid hybrid species between subsp. polymorpha and subsp. montivagans. Our study of Homalothecium shows that gametophytes from sympatric populations display intermediate morphology in a number of leaf characters, with the exception for leaf dimensions, which are strikingly smaller than those in allopatric populations. Most sporophytes with intermediate capsule inclination, initially classified as putative hybrids, did not display admixture of SNP markers. Many sporophytes appeared to be secondary hybrids by displaying asymmetrical admixture of SNP markers except five sporophytes, which were found to be primary hybrids. Admixture analyses using SNP markers identified 76 samples (17%) as mildly admixed and 17 samples (3.8%) as strongly admixed. Admixed samples represented all three generations and were found in all sympatric populations. Hybridization and introgression were bidirectional. Admixed sporophytes gave rise to viable recombinant spores and sporelings. Sporophytes with mildly admixed H. lutescens tended to show lower fitness, whereas sporophytes with mildly admixed H. sericeum showed signs of heterosis. Some strongly admixed sporophytes showed high spore counts, intermediate spore diameters and high spore germination rates. Genomic analysis showed three distinct taxa within the M. polymorpha complex, coinciding with the three generally accepted subspecies. All three possible topologies were frequent across the genome but species tree analyses using M. paleacea as outgroup recovered an overall branching order where subsp. montivagans…

Subjects/Keywords: Ecology; homozygote; heterozygote; admixture; single nucleotide polymorphism; STRUCTURE; PCoA; hybrid index; inbreeding; outbreeding; hybrid depression; heterosis; phylogeny; purging selection; genetic purging; genotype; phenotype; sympatry; allopatry

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APA (6th Edition):

Sawangproh, W. (2019). Gene transfer by interspecific hybridization in bryophytes. (Doctoral Dissertation). University of Lund. Retrieved from ;

Chicago Manual of Style (16th Edition):

Sawangproh, Weerachon. “Gene transfer by interspecific hybridization in bryophytes.” 2019. Doctoral Dissertation, University of Lund. Accessed December 05, 2020. ;

MLA Handbook (7th Edition):

Sawangproh, Weerachon. “Gene transfer by interspecific hybridization in bryophytes.” 2019. Web. 05 Dec 2020.


Sawangproh W. Gene transfer by interspecific hybridization in bryophytes. [Internet] [Doctoral dissertation]. University of Lund; 2019. [cited 2020 Dec 05]. Available from: ;

Council of Science Editors:

Sawangproh W. Gene transfer by interspecific hybridization in bryophytes. [Doctoral Dissertation]. University of Lund; 2019. Available from: ;