Lessons to Learn from Ancient Asexuals

Schön, Isa; Lamatsch, Dunja K.; Martens, Koen

doi:10.1007/7050_2007_032

Cited by 5 publications

(4 citation statements)

References 178 publications

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“…Nevertheless, multicellularity alone would not suffice to explain the costs of regular sexual reproduction. Volvocinae , as models of simple, differentiated multicellular organisms alternate between sexual and asexual reproduction (Lankenau, 2007), a strategy also seen in many asexual animals (Schön et al ., 2007); most asexual plants also have facultative sexuality (for example, Asker and Jerling, 1992). Still, the question remains: why regular sex?…”

Section: A Combinational Theory For the Evolution Of Sex In Eukaryotesmentioning

confidence: 99%

A combinational theory for maintenance of sex

Hörandl

2009

Heredity

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Sexual reproduction implies high costs, but it is difficult to give evidence for evolutionary advantages that would explain the predominance of meiotic sex in eukaryotes. A combinational theory discussing evolution, maintenance and loss of sex may resolve the problem. The main function of sex is the restoration of DNA and consequently a higher quality of offspring. Recombination at meiosis evolved, perhaps, as a repair mechanism of DNA strand damages. This mechanism is most efficient for DNA restoration in multicellular eukaryotes, because the initial cell starts with a re-optimized genome, which is passed to all the daughter cells. Meiosis acts also as creator of variation in haploid stages, in which selection can purge most efficiently deleterious mutations. A prolonged diploid phase buffers the effects of deleterious recessive alleles as well as epigenetic defects and is thus optimal for prolonged growth periods. For complex multicellular organisms, the main advantage of sexuality is thus the alternation of diploid and haploid stages, combining advantages of both. A loss of sex is constrained by several, partly group-specific, developmental features. Hybridization may trigger shifts from sexual to asexual reproduction, but crossing barriers of the parental sexual species limit this process. For the concerted break-up of meiosis-outcrossing cycles plus silencing of secondary features, various group-specific changes in the regulatory system may be required. An establishment of asexuals requires special functional modifications and environmental opportunities. Costs for maintenance of meiotic sex are consequently lower than a shift to asexual reproduction.

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Section: A Combinational Theory For the Evolution Of Sex In Eukaryotesmentioning

confidence: 99%

A combinational theory for maintenance of sex

Hörandl

2009

Heredity

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“…Furthermore, there are a number of eukaryote groups which seem to have reproduced without any sex for millions of years, the so-called ancient asexual scandals [10] . To date, four putative ancient asexual animal groups are known: bdelloid rotifers [11] , some lineages of oribatid mites [12] and stick insects [13] , and darwinulid ostracods [14] , [15] .…”

Section: Introductionmentioning

confidence: 99%

Cryptic Species in Putative Ancient Asexual Darwinulids (Crustacea, Ostracoda)

Schön

Pinto

Halse³

et al. 2012

PLoS ONE

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BackgroundFully asexually reproducing taxa lack outcrossing. Hence, the classic Biological Species Concept cannot be applied.Methodology/Principal FindingsWe used DNA sequences from the mitochondrial COI gene and the nuclear ITS2 region to check species boundaries according to the evolutionary genetic (EG) species concept in five morphospecies in the putative ancient asexual ostracod genera, Penthesilenula and Darwinula, from different continents. We applied two methods for detecting cryptic species, namely the K/θ method and the General Mixed Yule Coalescent model (GMYC). We could confirm the existence of species in all five darwinulid morphospecies and additional cryptic diversity in three morphospecies, namely in Penthesilenula brasiliensis, Darwinula stevensoni and in P. aotearoa. The number of cryptic species within one morphospecies varied between seven (P. brasiliensis), five to six (D. stevensoni) and two (P. aotearoa), respectively, depending on the method used. Cryptic species mainly followed continental distributions. We also found evidence for coexistence at the local scale for Brazilian cryptic species of P. brasiliensis and P. aotearoa. Our ITS2 data confirmed that species exist in darwinulids but detected far less EG species, namely two to three cryptic species in P. brasiliensis and no cryptic species at all in the other darwinulid morphospecies.Conclusions/SignificanceOur results clearly demonstrate that both species and cryptic diversity can be recognized in putative ancient asexual ostracods using the EG species concept, and that COI data are more suitable than ITS2 for this purpose. The discovery of up to eight cryptic species within a single morphospecies will significantly increase estimates of biodiversity in this asexual ostracod group. Which factors, other than long-term geographic isolation, are important for speciation processes in these ancient asexuals remains to be investigated.

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“…For proving absence of recombination and therefore anciency of parthenogenetic lineages the "Meselson effect" has been proposed (Welch and Meselson 2000). However, in each of the above mentioned three 'ancient asexual scandals' no Meselson effect has been detected (Butlin 2002, Schaefer et al 2006, Schön et al 2008.…”

Section: Sex Versus Parthenogenesismentioning

confidence: 97%

“…The widespread distribution of sexual reproduction in the animal kingdom despite its high costs (production of two sexes and the dilution of the genome through meiosis) has puzzled evolutionary biologist for decades and is known as "the queen of problems in evolutionary biology" (Bell 1982). Parthenogenetic species are thought to go extinct since they cannot overcome the accumulation of negative substitutions (Maynard Smith1978, Bell 1982, Kondrashov 1993, Butlin 2002, Schön et al 2008. The existence of so called "ancient asexual scandals" namely darwinulid ostracods (Martens et al 2003), bdelloid rotifers (Welch andMeselson 2000) and some taxa of oribatid mites (Maraun et al 2003) is still debated.…”

Section: Sex Versus Parthenogenesismentioning

confidence: 99%

Phylogeography in sexual and parthenogenetic European oribatida

Rosenberger¹

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Lessons to Learn from Ancient Asexuals

Cited by 5 publications

References 178 publications

A combinational theory for maintenance of sex

A combinational theory for maintenance of sex

Cryptic Species in Putative Ancient Asexual Darwinulids (Crustacea, Ostracoda)

Phylogeography in sexual and parthenogenetic European oribatida

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