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Quantifying the threat of extinction from Muller's ratchet in the diploid Amazon molly (Poecilia formosa)

Laurence Loewe12* and Dunja K Lamatsch3456

Author Affiliations

1 Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Ashworth Laboratories, King's Buildings, Edinburgh EH9 3JT, UK

2 Centre for Systems Biology Edinburgh, School of Biological Sciences, University of Edinburgh, Darwin Building, King's Buildings, Edinburgh EH9 3JU, UK

3 Universität Würzburg, Institute of Physiological Chemistry I, Biocenter, Würzburg, 97074 Würzburg, Germany

4 Freshwater Biology, Royal Belgian Institute of Natural Sciences, Vautierstraat 29, B – 1000 Brussels, Belgium

5 University of Sheffield, Department of Animal and Plant Sciences, Alfred Denny Building, Western Bank, Sheffield, S10 2TN, UK

6 Austrian Academy of Sciences, Institute for Limnology, Mondseestrasse 9, 5310 Mondsee, Austria

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BMC Evolutionary Biology 2008, 8:88  doi:10.1186/1471-2148-8-88

Published: 19 March 2008



The Amazon molly (Poecilia formosa) is a small unisexual fish that has been suspected of being threatened by extinction from the stochastic accumulation of slightly deleterious mutations that is caused by Muller's ratchet in non-recombining populations. However, no detailed quantification of the extent of this threat is available.


Here we quantify genomic decay in this fish by using a simple model of Muller's ratchet with the most realistic parameter combinations available employing the evolution@home global computing system. We also describe simple extensions of the standard model of Muller's ratchet that allow us to deal with selfing diploids, triploids and mitotic recombination. We show that Muller's ratchet creates a threat of extinction for the Amazon molly for many biologically realistic parameter combinations. In most cases, extinction is expected to occur within a time frame that is less than previous estimates of the age of the species, leading to a genomic decay paradox.


How then does the Amazon molly survive? Several biological processes could individually or in combination solve this genomic decay paradox, including paternal leakage of undamaged DNA from sexual sister species, compensatory mutations and many others. More research is needed to quantify the contribution of these potential solutions towards the survival of the Amazon molly and other (ancient) asexual species.