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Premise of research. The vast majority of eukaryotes reproduce by sexual reproduction, which is accompanied by meiotic recombination. Asexual reproduction, including the loss of meiosis, has been well characterized in several animal lineages but is vastly understudied in plants and particularly in the gametophyte life stage. Here, we explore the genomic consequences of strict clonal reproduction in the gametophyte-only fern Vittaria appalachiana. Methodology. Using publicly available transcriptome assemblies, we assessed how asexual reproduction can alter genomic features by comparing the transcriptomes of the asexually reproducing V. appalachiana (Pteridaceae) with sexually reproducing species in the same family, including congener Vittaria lineata. We explored several hypotheses relating asexual reproduction to the efficacy of purifying selection, transposable element load, GC-biased gene conversion, and the role of whole-genome duplications (WGDs). Pivotal results. We found putative support for predicted genomic consequences of asexual reproduction, including decreased efficacy of purifying selection (particularly in genes related to the cell cycle), altered transposable element load, and decreased GC content in V. appalachiana. We identified two putative WGDs, shared by Pteridaceae and the most recent common ancestor of the Vittaria genus, which may have contributed to V. appalachiana 's persistence over evolutionary time without sexual reproduction. Conclusions. Vittaria appalachiana is a gametophyte-only fern that is well suited to address fundamental questions regarding the long-term genomic effects of asexual reproduction in ferns, where this phenomenon has had little scientific attention in plants. This initial exploration into the genomic consequences of asexual reproduction is one of the first in ferns and highlights several avenues for future research. [ABSTRACT FROM AUTHOR]

Summary: Sex expression of homosporous ferns is controlled by multiple factors, one being the antheridiogen system. Antheridiogens are pheromones released by sexually mature female fern gametophytes, turning nearby asexual gametophytes precociously male. Nevertheless, not all species respond. It is still unknown how many fern species use antheridiogens, how the antheridiogen system evolved, and whether it is affected by polyploidy and/or apomixis.We tested the response of 68 fern species to antheridiogens in cultivation. These results were combined with a comprehensive review of literature to form the largest dataset of antheridiogen interactions to date. Analyzed species also were coded as apomictic or sexual and diploid or polyploid.Our final dataset contains a total of 498 interactions involving 208 species (c. 2% of all ferns). About 65% of studied species respond to antheridiogen. Multiple antheridiogen types were delimited and their evolution is discussed. Antheridiogen responsiveness was not significantly affected by apomixis or polyploidy.Antheridiogens are widely used by ferns to direct sex expression. The antheridiogen system likely evolved multiple times and provides homosporous ferns with the benefits often associated with heterospory, such as increased rates of outcrossing. Despite expectations, antheridiogens may be beneficial to polyploids and apomicts. [ABSTRACT FROM AUTHOR]

Homosporous vascular plants utilize three different mating systems, one of which, gametophytic selfing, is an extreme form of inbreeding only possible in homosporous groups. This mating system results in complete homozygosity in all progeny and has important evolutionary and ecological implications. Ferns are the largest group of homosporous land plants, and the significance of extreme inbreeding for fern evolution has been a subject of debate for decades., We cultured gametophytes in the laboratory and quantified the relative frequencies of sporophyte production from isolated and paired gametophytes, and examined associations between breeding systems and several ecological and evolutionary traits., The majority of fern species studied show a capacity for gametophytic selfing, producing sporophytes from both isolated and paired gametophytes. While we did not follow sporophytes to maturity to investigate potential detrimental effects of homozygosity at later developmental stages, our results suggest that gametophytic selfing may have greater significance for fern evolution and diversification than has previously been realized., We present evidence from the largest study of mating behavior in ferns to date that the capacity for extreme inbreeding is prevalent in this lineage, and we discuss its implications and relevance and make recommendations for future studies of fern mating systems. [ABSTRACT FROM AUTHOR]