The overlooked dwarf males in mosses—Unique among green land plants

Hedenäs, Lars; Bisang, Irene

doi:10.1016/j.ppees.2011.03.001

Cited by 39 publications

(42 citation statements)

References 144 publications

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“…It is not entirely known how fast the dwarf males develop after germination, but field observations (F Rosengren) suggest that dwarf males may fertilize the female the same year they were produced (after a couple of months) and/or over winter and fertilize the female the subsequent year. The prevailing opinion is that the dwarf males are unlikely to be able to live more than 1 or 2 years on the large shoots (Sagmo Solli et al, 1998;Hedenäs and Bisang, 2011;Hedenäs and Bisang, 2012). As dwarf males are frequently sterile, their true sexual identity is often unknown (male and female shoots lack distinguishing characters other than the sexual organs).…”

Section: Study Speciesmentioning

confidence: 99%

“…It has been estimated that 10-20% of all moss species (and at least 25% of all dioicous perennial pleurocarpous mosses) are nannandrous (also known as phyllodioicous), meaning that the males are situated as tiny epiphytes on a much larger female shoot (Hedenäs and Bisang, 2011). These so-called 'dwarf males' originate from male spores that happen to land on a mature female shoot.…”

Section: Introductionmentioning

confidence: 99%

“…Consequently, the female shoot and its male progeny (that will become the next generation of dwarf males) may have a high genetic similarity. High levels of inbreeding have been suggested as a potential consequence of the dwarf male sexual system in bryophytes (Mogensen, 1981;Ramsay, 1985;Hedenäs and Bisang, 2011;Pichonet and Gradstein, 2012). Because of the dominant haploid life stage, inbreeding in bryophytes may have more drastic genetic effects compared with diploids.…”

Section: Introductionmentioning

confidence: 99%

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Balance between inbreeding and outcrossing in a nannandrous species, the moss Homalothecium lutescens

2015

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Epiphytic dwarf males on the females present a possible solution to the problem of short fertilization distances in mosses. However, leptokurtic spore dispersal makes dwarf males likely to be closely related to their host shoot, with an accompanying risk of inbreeding. The capacity of a female to harbour a high number of different dwarf males suggests that there may be mechanisms in place that counteract inbreeding, such as polyandry and post-fertilization selection. We have genotyped sporophytes, female host shoots and dwarf males in four populations of the moss Homalothecium lutescens. We found no evidence of selective sporophyte abortion based on level of heterozygosity. The occurrence of entirely homozygous sporophytes together with significantly positive inbreeding coefficients in three of the populations (mean F IS between 0.48 and 0.64) suggest frequent mother-son mating events. However, 23% of all sampled sporophytes had a higher level of heterozygosity compared with the mean expected heterozygosity at the population level. Polyandry was frequent, on average 59% of the sporophytes on a female shoot were sired by distinct fathers. In conclusion, sporadic fertilizations by dwarf males originating from nonhost female shoots appear to counteract strong inbreeding.

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Section: Study Speciesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Balance between inbreeding and outcrossing in a nannandrous species, the moss Homalothecium lutescens

2015

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“…Tiny males grow epiphytically on much larger females in many moss species [53,54]. Males are sometimes reduced to no more than a few leaves sheathing a single antheridium [55].…”

Section: (B) Dwarf Malesmentioning

confidence: 99%

“…Male dwarfs are facultative in some species but obligate in others. In one survey, dwarf males were detected in 72 out of 162 (44%) dioecious mosses, with full-sized males unknown in 18 of these species [54]. Male dwarfism appears to have evolved many times independently [54,56].…”

Section: (B) Dwarf Malesmentioning

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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