The Elusive Clone – In Search of Its True Nature and Identity

BackgroundQuest for understanding the nature of mechanisms governing the life span of clonal organisms lasts for several decades. Phylogenetic evidence for recent origins of most clones is usually interpreted as proof that clones suffer from gradual age-dependent fitness decay (e.g. Muller's ratchet). However, we have shown that a neutral drift can also qualitatively explain the observed distribution of clonal ages. This finding was followed by several attempts to distinguish the effects of neutral and non-neutral processes. Most recently, Neiman et al. 2009 (Ann N Y Acad Sci.:1168:185-200.) reviewed the distribution of asexual lineage ages estimated from a diverse array of taxa and concluded that neutral processes alone may not explain the observed data. Moreover, the authors inferred that similar types of mechanisms determine maximum asexual lineage ages in all asexual taxa. In this paper we review recent methods for distinguishing the effects of neutral and non-neutral processes and point at methodological problems related with them.Results and DiscussionWe found that contemporary analyses based on phylogenetic data are inadequate to provide any clear-cut answer about the nature and generality of processes affecting evolution of clones. As an alternative approach, we demonstrate that sequence variability in asexual populations is suitable to detect age-dependent selection against clonal lineages. We found that asexual taxa with relatively old clonal lineages are characterised by progressively stronger deviations from neutrality.ConclusionsOur results demonstrate that some type of age-dependent selection against clones is generally operational in asexual animals, which cover a wide taxonomic range spanning from flatworms to vertebrates. However, we also found a notable difference between the data distribution predicted by available models of sequence evolution and those observed in empirical data. These findings point at the possibility that processes affecting clonal evolution differ from those described in recent studies, suggesting that theoretical models of asexual populations must evolve to address this problem in detail.ReviewersThis article was reviewed by Isa Schön (nominated by John Logsdon), Arcady Mushegian and Timothy G. Barraclough (nominated by Laurence Hurst).

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“…We also shortened the part elaborating on asexual species definition and use the concept of a clone discussed by Martens et al [32]. …”

Section: Reviewers' Commentsmentioning

confidence: 99%

Do clones degenerate over time? Explaining the genetic variability of asexuals through population genetic models

2011

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“…As a result, the true nature of the aphid clone, and indeed clones in general, is not simply just one of semantics, but rather, concerns a scientifically important re-appraisal, perhaps including re-definition of the phenomenon (Martens et al 2009). …”

Section: Introductionmentioning

confidence: 97%

Continuous occurrence of intra-individual chromosome rearrangements in the peach potato aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae)

et al. 2012

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Analysis of the holocentric mitotic chromosomes of the peach-potato aphid, Myzus persicae (Sulzer), from clones labelled 50, 51 and 70 revealed different chromosome numbers, ranging from 12 to 14, even within each embryo, in contrast to the standard karyotype of this species (2n = 12). Chromosome length measurements, combined with fluorescent in situ hybridization experiments, showed that the observed chromosomal mosaicisms are due to recurrent fragmentations of chromosomes X, 1 and 3. Contrary to what has generally been reported in the literature, X chromosomes were frequently involved in recurrent fragmentations, in particular at their telomeric ends opposite to the nucleolar organizer region. Supernumerary B chromosomes have been also observed in clones 50 and 51. The three aphid clones showed recurrent fissions of the same chromosomes in the same regions, thereby suggesting that the M. persicae genome has fragile sites that are at the basis of the observed changes in chromosome number. Experiments to induce males also revealed that M. persicae clones 50, 51 and 70 are obligately parthenogenetic, arguing that the reproduction by apomictic parthenogenesis favoured the stabilization and inheritance of the observed chromosomal fragments.

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“…). Clones are thus defined sensu Martens et al (), that is as all descendants of a unique founder derived from sexual ancestor.…”

Section: Methodsmentioning

confidence: 99%

Let Us Not Be Unfair to Asexuals: Their Ephemerality May Be Explained by Neutral Models Without Invoking Any Evolutionary Constraints of Asexuality

Janko

2013

Evolution

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The Elusive Clone – In Search of Its True Nature and Identity

Cited by 17 publications

References 55 publications

Do clones degenerate over time? Explaining the genetic variability of asexuals through population genetic models

Do clones degenerate over time? Explaining the genetic variability of asexuals through population genetic models

Continuous occurrence of intra-individual chromosome rearrangements in the peach potato aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae)

Let Us Not Be Unfair to Asexuals: Their Ephemerality May Be Explained by Neutral Models Without Invoking Any Evolutionary Constraints of Asexuality

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