Gametophytes of Four Tropical Fern Genera Reproducing Independently of Their Sporophytes in the Southern Appalachians

Farrar, Donald R.

doi:10.1126/science.155.3767.1266

Cited by 104 publications

(58 citation statements)

References 7 publications

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“…Among the taxa examined in our study, the strongest evidence for ancient asexuality is in Vittaria appalachiana, where patterns of geographical distribution and genetic diversity indicate an age of at least 10 million years (Farrar 1967(Farrar , 1978(Farrar , 1990. A study of allozyme diversity in Vittaria showed V. appalachiana to have no recent origin from or close relation to sexual Vittaria species (Farrar 1985(Farrar , 1990.…”

Section: Possible Explanations For the Pattern Of Conserved Te Sequenmentioning

confidence: 99%

“…In temperate regions of North America (from Alabama to New York), populations of V. appalachiana exist as independent gametophytes (i.e., with no sporophyte generation) and persist via the production of vegetative propagules termed ''gemmae.'' These populations are thought to be conspecific or closely related to the tropical species V. lineata (shoestring fern), which exists as both sporophyte and gametophyte, and reproduces sexually (Farrar 1967).…”

Section: Plant Taxamentioning

confidence: 99%

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Retrotransposon Sequence Variation in Four Asexual Plant Species

et al. 2006

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Abstract. Transposable elements (TEs) can be viewed as genetic parasites that persist in populations due to their capacity for increase in copy number and the inefficacy of selection against them. A corollary of this hypothesis is that TEs are more likely to spread within sexual populations and be eliminated or inactivated within asexual populations. While previous work with animals has shown that asexual taxa may contain less TE diversity than sexual taxa, comparable work with plants has been lacking. Here we report the results of a study of Ty1/copia, Ty3/ gypsy, and LINE-like retroelement diversity in four asexual plant species. Retroelement-like sequences, with a high degree of conservation both within and between species, were isolated from all four species. The sequences correspond to several previously annotated retroelement subfamilies. They also exhibit a pattern of nucleotide substitution characterized by an excess of synonymous substitutions, suggestive of a history of purifying selection. These findings were compared with retroelement sequence evolution in sexual plant taxa. One likely explanation for the discovery of conserved TE sequences in the genomes of these asexual taxa is simply that asexuality within these taxa evolved relatively recently, such that the loss and breakdown of TEs is not yet detectable through analysis of sequence diversity. This explanation is examined by conducting stochastic simulation of TE evolution and by using published information to infer rough estimates of the ages of asexual taxa.

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Section: Possible Explanations For the Pattern Of Conserved Te Sequenmentioning

confidence: 99%

Section: Plant Taxamentioning

confidence: 99%

Retrotransposon Sequence Variation in Four Asexual Plant Species

et al. 2006

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“…Gemma-producing species sometimes exist as populations that are dominated by gametophytes rather than sporophytes (e.g. Dassler & Farrar 1997) and have on multiple occasions given rise to gametophyte-only populations that reproduce clonally (Farrar 1967(Farrar , 1990.…”

Section: Pteridophytesmentioning

confidence: 99%

Sexual conflict and the alternation of haploid and diploid generations

Haig

Wilczek

2006

Phil. Trans. R. Soc. B

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Land plants possess a multicellular diploid stage (sporophyte) that begins development while attached to a multicellular haploid progenitor (gametophyte). Although the closest algal relatives of land plants lack a multicellular sporophyte, they do produce a zygote that grows while attached to the maternal gametophyte. The diploid offspring shares one haploid set of genes with the haploid mother that supplies it with resources and a paternal haploid complement that is not shared with the mother. Sexual conflict can arise within the diploid offspring because the offspring's maternal genome will be transmitted in its entirety to all other sexual and asexual offspring that the mother may produce, but the offspring's paternally derived genes may be absent from these other offspring. Thus, the selective forces favouring the evolution of genomic imprinting may have been present from the origin of modern land plants. In bryophytes, where gametophytes are long-lived and capable of multiple bouts of asexual and sexual reproduction, we predict strong sexual conflict over allocation to sporophytes. Female gametophytes of pteridophytes produce a single sporophyte and often lack means of asexual reproduction. Therefore, sexual conflict is predicted to be attenuated. Finally, we explore similarities among models of mate choice, offspring choice and segregation distortion.

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“…Most ferns, by contrast, propagate as perennial sporophytes and possess gametophytes that lack means of asexual reproduction. Gametophytic production of gemmae, however, has evolved in three families of predominantly epiphytic ferns [106]. Some of these ferns exist as self-perpetuating populations of gametophytes with rare, short-lived sporophytes.…”

Section: (B) Asexual Comparisonsmentioning

confidence: 99%

Living together and living apart: the sexual lives of bryophytes

Haig¹

2016

Phil. Trans. R. Soc. B

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One contribution of 15 to a theme issue 'Weird sex: the underappreciated diversity of sexual reproduction'. Haploid gametophytes of bryophytes spread by clonal growth but mate locally, within an area defined by the range of sperm movement. Rarity of establishment from spores or vegetative competition can result in unisexual populations unable to reproduce sexually. Females typically outcompete males, probably because females expend fewer resources than males on the production of gametes. Extreme sexual dimorphism-tiny males growing as epiphytes on much larger females-has evolved many times. Haploid selfing is common in bryophytes with bisexual gametophytes, and results in completely homozygous sporophytes. Spores from these sporophytes recapitulate the genotype of their single haploid parent. This process can be considered analogous to 'asexual' reproduction with 'sexual' reproduction occurring after rare outcrossing between haploid parents. Ferns also produce bisexual haploid gametophytes but, unlike bryophytes, haploid outcrossing predominates over haploid selfing. This difference is probably related to clonal growth and vegetative competition occurring in the haploid but not the diploid phase in bryophytes, but the reverse in ferns. Ferns are thereby subject to stronger inbreeding depression than bryophytes.This article is part of the themed issue 'Weird sex: the underappreciated diversity of sexual reproduction'. Sexual lives of bryophytesAnimal life histories are characterized by multicellular diploid individuals that produce haploid gametes by meiosis. Gametes are the only haploid cells of such life cycles. The life histories of bryophytes (mosses, liverworts and hornworts) are fundamentally different. Multicellular haploid gametophytes (gameteproducing plants) produce gametes by mitosis. The fertilization of an ovum by a sperm produces a zygote that develops into a short-lived multicellular diploid sporophyte (spore-producing plant) that grows attached to the maternal gametophyte on which it depends for nutrients. Sporophytes produce haploid spores by meiosis that germinate to produce new gametophytes (figure 1). Mating is restricted to the distance over which sperm can find ova, usually in the millimetre to centimetre range [1]. Clonal expansion occurs via vegetative spread of gametophytes into neighbouring space and production of gemmae (asexual propagules) that disperse gametophytic clones to new sites [2].Gametophytes of dioecious bryophytes are unisexual, producing either eggs or sperm, but not both. Males and females compete for space but require close proximity for sexual reproduction. By contrast, gametophytes of monoecious bryophytes are bisexual, able to produce both eggs and sperm. A bisexual gametophyte that fertilizes its own eggs engenders homozygous sporophytes all of whose spores are genetically identical (excepting meiotic errors and postzygotic mutations). Roughly 70% of liverworts, 60% of mosses and 40% of hornworts are dioecious [3]. Bryophyte life cycles are not only fascinating in th...

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Gametophytes of Four Tropical Fern Genera Reproducing Independently of Their Sporophytes in the Southern Appalachians

Cited by 104 publications

References 7 publications

Retrotransposon Sequence Variation in Four Asexual Plant Species

Retrotransposon Sequence Variation in Four Asexual Plant Species

Sexual conflict and the alternation of haploid and diploid generations

Living together and living apart: the sexual lives of bryophytes

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