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Sex increases the efficacy of natural selection in experimental yeast populations


Why sex evolved and persists is a problem for evolutionary biology, because sex disrupts favourable gene combinations and requires an expenditure of time and energy1. Further, in organisms with unequal-sized gametes, the female transmits her genes at only half the rate of an asexual equivalent (the twofold cost of sex)2. Many modern theories that provide an explanation for the advantage of sex incorporate an idea originally proposed by Weismann more than 100 years ago: sex allows natural selection to proceed more effectively because it increases genetic variation3,4,5. Here we test this hypothesis, which still lacks robust empirical support, with the use of experiments on yeast populations. Capitalizing on recent advances in the molecular biology of recombination in yeast, we produced by genetic manipulation strains that differed only in their capacity for sexual reproduction. We show that, as predicted by the theory, sex increases the rate of adaptation to a new harsh environment but has no measurable effect on fitness in a new benign environment where there is little selection.

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Figure 1: The change in natural logarithm of fitness of asexual and sexual populations of yeast in benign and harsh environments.

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We thank M. Rees for comments on statistical analyses. This work was supported by the UK Natural Environment Research Council (NERC).

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Correspondence to Matthew R. Goddard.

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The authors declare that they have no competing financial interests.

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This file contains more detailed descriptions of the methods used in this study. (DOC 37 kb)

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Goddard, M., Godfray, H. & Burt, A. Sex increases the efficacy of natural selection in experimental yeast populations. Nature 434, 636–640 (2005).

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