Sex increases the efficacy of natural selection in experimental yeast populations

Abstract

Why sex evolved and persists is a problem for evolutionary biology, because sex disrupts favourable gene combinations and requires an expenditure of time and energy. 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). 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 variation. 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.

Eukaryotic microbes, species recognition and the geographic limits of species: examples from the kingdom Fungi

“…Sexual reproduction with some outcrossing maintains cohesion within species, whereas reproductive isolation leads to the formation of new species (Coyne & Orr 1998). Recombination has been shown to facilitate more rapid adaptation than clonality (Goddard et al 2005) and recombining organisms may show larger and more phenotypic differences among species. These effects may increase the chance that newly diverged species will have adapted to different niches and be able to coexist, provided that they are reproductively isolated in sympatry (Felsenstein 1981;Barraclough et al 2003).…”

“…Recently, Barraclough et al (2003) considered theoretical aspects of speciation by organisms that can recombine or that are strictly clonal to see if there were any fundamental differences. They conclude that both clonal and recombining organisms will form species, but that recombining organisms may form them faster because they respond more rapidly to selection (Goddard et al 2005). Barraclough et al (2003) note that speciation involves not only divergence, but also maintenance, particularly when newly derived species coexist.…”

What happened and what's next?

“…One of the earliest clues was the delineation, within just hours of the mainshock,of a band of large aftershocks arcing 1,300 km from northern Sumatra almost as far as Myanmar (Burma) 1 . This seemed to signal that about 25% of the Sunda megathrust, the great tectonic boundary along which the Australian and Indian plates begin their descent beneath Southeast Asia, had ruptured.…”

Sex accelerates adaptation

“…A series of experimental evolution studies support the idea that sex speeds adaptive evolution [6][7][8] . However, much less work has focused on the molecular mechanisms underpinning this advantage.…”