Abstract
Author SummaryFor well over a century, biologists have wondered why sex is such a common mode of reproduction, given the immediate 2-fold fitness cost entailed by the reduced number of offspring per parent. The most classic explanation is that sex is favoured because it helps to generate the variation necessary for adaptation. While theoretical models and indirect lines of evidence support this idea, there are no direct experimental data and it is far from obvious whether any such advantage could balance the considerable costs of sex. Using experimental populations of a facultatively sexual species of rotifer, we demonstrate that rates of sex evolutionarily increase as populations adapt to novel environments. We show that sex creates a diverse array of genotypes, including many that are quite unfit but also others that are very fit in the new environment. Though the average fitness of these sexually derived offspring is lower than that of asexuals, those well-adapted genotypes generated by sex contribute disproportionately to future generations, causing the genetic propensity for sex to ultimately increase.
Highlights
The pervasiveness of sex, given its varied and potentially large costs, is highly perplexing [1,2,3,4,5,6,7,8,9,10]
The idea is not necessarily correct as sex will increase the variance in fitness only if there is a preponderance of ‘‘negative genetic associations’’ such that good alleles are often found in genomes with bad alleles
The most classic explanation is that sex is favoured because it helps to generate the variation necessary for adaptation
Summary
The pervasiveness of sex, given its varied and potentially large costs, is highly perplexing [1,2,3,4,5,6,7,8,9,10]. It was later realized that such negative associations may develop under certain forms of nonlinear selection (as occurs when approaching an adaptive optimum [21,22,23,24,25]) or, perhaps more importantly, due to an interaction between directional selection and drift, known as the Hill-Robertson effect [6,26]. For these more sophisticated reasons, Weismann’s original conjecture is thought to be valid and is considered by many as the leading explanation for the evolutionary function of sex [27]
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