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No evidence for accumulation of deleterious mutations and fitness degradation in clonal fish hybrid: Abandoning sex without regrets
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  • Jan Kočí,
  • Jan Röslein,
  • Jan Pačes,
  • Jan Kotusz,
  • Karel Halacka,
  • Ján Koščo,
  • Jakub Fedorčák,
  • Nataliia Iakovenko,
  • Karel Janko
Jan Kočí
University of Ostrava
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Jan Röslein
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Jan Pačes
Institute of Molecular Genetics of the ASCR, v. v. i.
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Jan Kotusz
University of Wroclaw
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Karel Halacka
Institute of Vertebrate Biology, v.v.i.
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Ján Koščo
University of Prešov
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Jakub Fedorčák
University of Prešov
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Nataliia Iakovenko
University of Ostrava
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Karel Janko
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Abstract

Despite its inherent costs, sexual reproduction is ubiquitous in nature, and the mechanisms to protect it from a competitive displacement by asexuality remain unclear. Popular mutation-based explanations, like the Muller's ratchet and the Kondrashov's hatchet, assume that purifying selection may not halt the accumulation of deleterious mutations in the non-recombining genomes, ultimately leading to their degeneration. However, empirical evidence is scarce and it remains particularly unclear whether mutational degradation proceeds fast enough to ensure the decay of clonal organisms and to prevent them from outcompeting their sexual counterparts. To test this hypothesis, we jointly analyzed the exome sequences and the fitness-related phenotypic traits of the sexually-reproducing fish species and their clonal hybrids, whose evolutionary ages ranged from F1 generations to 300 ky. As expected, mutations tended to accumulate in the clonal genomes in a time-dependent manner. However, contrary to the predictions, we found no trend towards increased non-synonymity of mutations acquired by clones, nor higher radicality of their amino-acid substitutions. Moreover, there was no evidence for fitness degeneration in the old clones compared to that in the younger ones. In summary, although a purifying selection may still be relaxed in the asexual genomes, our data indicate that its efficiency is not drastically decreased. Even the oldest investigated clone was found to be too young to suffer fitness consequences from a mutation accumulation. This suggests that mechanisms other than mutation accumulation may be needed to explain the competitive advantage of sex in the short term.

Peer review status:ACCEPTED

19 Feb 2020Submitted to Molecular Ecology
10 Apr 2020Reviewer(s) Assigned
04 May 2020Review(s) Completed, Editorial Evaluation Pending
05 May 2020Editorial Decision: Revise Minor
18 Jun 2020Review(s) Completed, Editorial Evaluation Pending
18 Jun 20201st Revision Received
22 Jun 2020Editorial Decision: Accept