Abstract
Peatmosses are interesting for studies of speciation processes not only because of their frequent hybridization and recent diversification, but also their phenotypic diversity, ecological importance and ancient history. Diverse and widespread hybridization has been widely documented in the genus, but little is known about what factors underlie this phenomenon. We hypothesize that these factors include phylogenetic distance and variation in life-history traits of parental species. We summarize current knowledge about the occurrence of hybridization in peatmosses and explore how it is associated with phylogenetic distance and life-history trait variation of parental species. Possibly as much as one out of five (or more) peatmoss species hybridize, mostly producing allopolyploid hybrids. Parents of admixed haploids are more closely related to each other than parents of allopolyploids. Hybridization seems to be most frequent in 1) monoicous and polyoicous species exhibiting 2) relatively high sporulation frequency, 3) producing relatively small spores, as well as 4) growing in poor habitats. Surprisingly, neither phylogenetic proximity nor life-history trait variation explain patterns of hybridization in peatmosses, and other likely explanations for patterns observed are discussed.
Highlights
Numerous studies have demonstrated that hybridization is common across old, species-rich lineages of bryophytes and might have been one of the key factors underlying speciation in these plants (Wyatt et al 1988, Natcheva and Cronberg 2004, Stenøien et al 2011b, Shaw et al 2015)
In this paper we aim to 1) summarize evidence of hybridization in peatmosses, 2) explore how phylogenetic distance and life-history traits are associated with hybridization and interspecific gene flow, and 3) discuss in what way interspecific gene flow can influence speciation in peatmosses
As our data set contained both categorical and continuous variables, we explored it with factorial analysis of mixed data (FAMD) using the FactoMineR package in R (Lê et al 2008), and used the missMDA package in R (Josse and Husson 2016) to account for missing trait values within some species
Summary
Numerous studies have demonstrated that hybridization is common across old, species-rich lineages of bryophytes and might have been one of the key factors underlying speciation in these plants (Wyatt et al 1988, Natcheva and Cronberg 2004, Stenøien et al 2011b, Shaw et al 2015). Genetic structure of modern peatmoss populations is shaped by past and on-going gene flow and intercontinental distributions of many species are thought to reflect high potential of dispersal in the genus (Sundberg 2000, Szövényi et al 2008, Stenøien et al 2011b, Karlin et al 2013, Shaw et al 2014, Kyrkjeeide et al 2016b). Allopolyploid: a hybrid individual with ploidy level of two (or more), and having resulted from interspecific crosses. Autopolyploid: a hybrid individual with ploidy level of two (or more), and having resulted from intraspecific crosses
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