Credit: Manfred Schartl, University of Würzburg.

Snubbing sex a genetic win for this Amazon female fish

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A fish species that has spurned sex and instead clones itself to reproduce has been found to have surprisingly healthy genes, according to international researchers. The fish species, dubbed the Amazon molly, is made up entirely of females and is named after the all-women warriors of Greek mythology. Scientists had thought the species might be at a genetic disadvantage without the variation that sexual reproduction can bring. Instead, they found few harmful mutations and a high degree of genetic diversity, especially in the genes for the immune system.

Journal/conference: Nature Ecology and Evolution

Link to research (DOI): 10.1038/s41559-018-0473-y

Organisation/s: Washington University St Louis, USA

Funder: This work was supported by grants to W.C.W. (NIH: 2R24OD011198-04A1), M.W.H. (NSF DBI-1564611), M.S. (German Research Foundation DFG projects Scha408/10-1 and Scha408/12-1), M.St. (Heisenberg-Fellowship STO 493/2-2 of the German Science Foundation/DFG), T.M.B. (MINECO BFU2014-55090-P (FEDER), U01 MH106874 grant, Howard Hughes International Early Career, Obra Social ‘La Caixa’ and Secretaria d’Universitats i Recerca del Departament d’Economia i Coneixement de la Generalitat de Catalunya) and R.B.W. (NIH: R24OD011120). The genome annotation work carried out by NCBI was supported by the Intramural Research Program of the NIH, National Library of Medicine. The genome annotation work by Ensembl was supported by funding from the Wellcome Trust (WT108749/Z/15/Z and WT098051), the National Institutes of Health (R24 RR032658-01) and the European Molecular Biology Laboratory.

Media Release

From: Springer Nature

Genome of rare asexual fish explains its success (N&V)

The genome of the asexual fish, the Amazon molly, reveals remarkable good health, reports a study published online this week in Nature Ecology & Evolution. This finding is unexpected, as asexual reproduction is assumed to cause genomes to decay.

Theory predicts several disadvantages of asexual reproduction, such as the accumulation of harmful mutations which lead to genomic decay and eventual extinction. Another challenge is that asexual organisms lack the genetic diversity generated through sexual reproduction, which is important for adapting to new environmental conditions. Organisms that reproduce asexually are thus often considered a biological paradox.

Asexual vertebrates are extremely rare. There are only about 50 naturally occurring fish, amphibian, and reptile species that reproduce asexually. The Amazon molly, Poecilia formosa, was the first all-female vertebrate species described back in 1932. Its common name refers to the Amazons, the all-women warriors of Greek mythology.

The Amazon molly is a hybrid of two distantly related sexual species, and its evolutionary and ecological successes are remarkable—the molly has a long existence and has colonized diverse habitats over a wide geographical range.

Manfred Schartl, and colleagues sequenced the Amazon molly genome and, contrary to expectations, found few harmful mutations, little genetic decay, and a high degree of genetic diversity. The molly genome also reveals a remarkable level of variability in genes relating to immunity. The authors argue that the combination of genetic diversity and broad immune defenses might have allowed the Amazon molly to escape the common fate of asexual organisms—being an easy target for pathogens.

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