Experimental studies of ploidy evolution in yeast

Abstract

Variation in the prominence of haploidy and diploidy is a striking feature of eukaryote life cycles that has not been explained from an evolutionary point of view. the ease with which ploidy and other variables of population genetics may be manipulated in yeast make Saccharomyces cerevisiae an excellent subject for experiments on the fitness effects of ploidy. Several hypotheses have been advanced to explain the emphasis on diploidy in plants and animals, and yeast experiments have been particularly informative for a few. Evidence suggests that diploids may enjoy an immediate advantage over haploids in masking harmful mutations, avoiding the fitness cost such mutations impose on haploids. A convincing longer-term advantage for diploidy has proven elusive, and different evolutionary explanations for the origin and for the subsequent maintenance of diploidy may be required.

Can resource costs of polyploidy provide an advantage to sex?

“…Of most direct relevance to our hypothesis is empirical evidence from algae and yeast suggesting that haploids are better competitors than diploids in low-P environments (Adams and Hansche, 1974;Destombe et al, 1993;Zeyl, 2004; but see Mable, 2001). Several well-established broad-scale biogeographical patterns are consistent with hypotheses relating nuclear DNA content to dietary P availability, though whether these patterns are directly linked to P limitation remains untested.…”

“…The idea that ploidy affects organismal ecology has a long history (Vandel, 1928;Stebbins, 1938;Suomalainen, 1950;Cavalier-Smith, 1978;Bell, 1982;Levin, 1983;Bierzychudek, 1985), but there is still no consensus on whether there are definitive advantages or costs of polyploidy that can explain its frequency and distribution (Mable and Otto, 1998;Mable, 2001;Ramsey and Schemske, 2002;Zeyl, 2004;Buggs and Pannell, 2007;Gerstein and Otto, 2009;Soltis et al, 2010;Beck et al, 2011;Mayrose et al, 2011;Ramsey, 2011). The advantages and disadvantages of polyploidy and its relevance to the distribution and maintenance of sex have been reviewed extensively (Bierzychudek, 1985 The ecological consequences of polyploidy are difficult to empirically disentangle from those directly related to asexuality, with which it is so often associated (Bierzychudek, 1985;Otto and Whitton, 2000;Hörandl, 2006;Mable et al, 2011).…”

Molecular-Genetic Biodiversity in a Natural Population of the YeastSaccharomyces cerevisiaeFrom “Evolution Canyon”: Microsatellite Polymorphism, Ploidy and Controversial Sexual Status

“…In recent decades, evolution of ploidy level became an important subject within the problems of genome molecular evolution and sex evolution. In particular, yeast may be a very relevant model organism for such studies (e.g., Wolfe and Shields 1997;Mable and Otto 1998;Korona 1999;Mable and Otto 2001;Wolfe 2001;Zeyl 2004). It is noteworthy that the recent renaissance of the polyploidy studies is, to a large extent, due to the interest in the (presumably existing) mechanisms of (very) fast evolution of polyploid genomes toward diploidization and novel tools allowing us to address this ''old'' problem (Belyayev et al 2000;Ozkan et al 2001;Feldman and Levy 2005).…”

Evolution of the hemiascomycete yeasts: on life styles and the importance of inbreeding

“…Moreover, haploid growth elicits direct selection for mutations based on the fitness that they provide, and irrespective of whether they are dominant or recessive. (47)(48)(49)(50)(51)(52)(53) Various evolutionary advantages for haploid as well as diploid populations have been demonstrated experimentally. (54,55) Quantification of the impact of haploidy and diploidy is complicated by the variable influences and requirements of the environments that different species inhabit and from the morphological and genetical constraints to which they are subjected.…”