Yoyo@home and Evolution@home quantified Mullers ratchet in worm C. elegans

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Yoyo@home is currently running an application for another project called Evolution@home. The small worm Caenorhabditis elegans is known for his high rate of selfing that may make it susceptible to the operation of Muller's ratchet. Now evolution@home has found that this worm would indeed be in trouble if there were no processes that would counter genomic decay in this worm or if selfing was very old.

<= The image on the left displays C. elegans hermaphrodite crawling half out of the bacterial lawn it feeds upon. (Picture credit: Asher D. Cutter)

Most worms that belong to the species Caenorhabditis elegans are hermaphrodites, which means that male and female functions are in the same individual. Only few males exist in this species that mainly feeds on bacteria. Conveniently, hermaphrodite C. elegans can produce offspring by "selfing", which does not require the presence of a partner and leads to the recombination of one part of its genome with another.

Estimates of the frequency of outcrossing (the opposite of selfing) have suggested that many strains in this worm are almost exclusively selfing, with only abot one outcrossing event in 10 000 generations. This raises the possibility that Muller's ratchet could degrade the fitness of such strains and lead to their extinction.

C. elegans hermaphrodite Using realistic values that describe various measures of the evolution of this worm, evolution@home tested how long C. elegans could survive pure selfing. Results were computed on Simlator005 and indicate that this timespan is shorter than current estimates for the time since the separation from its closest outcrossing relative.

These results may place upper limits on the age of selfing in this evolutionary line, unless other factors prolong the survival of this small worm.

This study was done together with Asher D. Cutter (Lab at Uni Toronto) and has been published in the journal "BMC Evolutionary Biology". It is freely available for download (PDF).

Evolution@home plans to eventually return modelling efforts to C. elegans to test what happens, if very low levels of outcrossing are present. However, this cannot be done with Simulator005 and will thus take considerable time.

You can read more about the Yoyo@home project here.

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