S P Otto

..When selection at the cell and individual levels act in a cooperative manner, increased rather than decreased opportunity for germline selection will be favored by evolution...

..Theoretical advances improve our ability to distinguish signals left by different evolutionary processes. In particular, a new test might better detect the footprint of selection having favored the spread of a beneficial allele...

..New studies indicate that this discrepancy might result from the fact that previous models have ignored important complexities that face natural populations, such as genetic drift and the spatial structure of populations...

..In contrast, with a Z-linked trait (males ZZ, females ZW), females more often evolve mating preferences for mates carrying alleles beneficial to sons (that is, flashy displays)...

..These results demonstrate that, at least under certain circumstances, selection acting on asexual fitness can help to maintain sexual function...

..We conclude that, even with negative epistasis, increased recombination may only be favored when linkage is tight, especially if, as seems likely, epistatic interactions are highly variable among loci...

..Consideration of each of the short-term and long-term processes affecting duplicated genes illustrates the subtle ways in which selection has acted to shape genomic structure...

..Here, we review various hypotheses for why sex and recombination are so prevalent and discuss theoretical results indicating which of these hypotheses is most promising...

..This Review examines the short-term effects of polyploidization on cell size, body size, genomic stability, and gene expression and the long-term effects on rates of evolution...

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..Our results show that species interactions typically select against sex. We conclude that, although the Red Queen favors sex under certain circumstances, it alone does not account for the ubiquity of sex...

..These results help to shape our understanding of the evolutionary inertia caused by pleiotropy...

..Selection for a modifier that increases recombination is highest when linkage among loci is tight, when beneficial alleles rise from low to high frequency, and when the population size is small...

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..These recent efforts have clarified the conditions that are most likely to explain why sex is so common, as exemplified by the articles in this symposium issue of the American Naturalist...

..We conclude that selection for recombination will be substantial only if there is tight linkage within the genome or if many loci are subject to directional selection as during periods of rapid evolutionary change...

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..We therefore suggest that the QTL-based estimator be used to assess how many loci may have been missed in QTL studies...

..The fixation flux measures the rate of adaptive evolution of a population and, as we shall see, depends strongly on changes that occur in population size...

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..Overall, our results show that the stochastic theories of the evolution of sex apply to a much broader range of conditions than previously expected...

..In each case, predicting whether recombination is favored requires knowledge of both the type of environmental heterogeneity and epistasis, as none of these factors alone is sufficient to predict the outcome...

..The mechanism supported by our results offers a robust and broadly applicable explanation for the evolutionary advantage of recombination and can explain the spread of costly sex...

..Our results have implications for models of sequence evolution, including those used for phylogenetic reconstruction and for inferring unusual changes in GC content...

..The conditions promoting increased levels of sex depend on the selection pressure against the homozygotes, the extent of sex and inbreeding in the population, and the dominance of the invading modifier allele...

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..These results suggest that the maintenance of dioecy in the presence of hermaphroditic competitors requires a substantial increase in relative fitness and/or a large dispersal advantage of dioecious seeds...

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..It may also help explain why dioecious plants are less species-rich than related bisexual plants...

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..Our model shows that stable coexistence of gynogens and their sexual hosts can occur when there is variation among males in the degree of preference for mating with sexual females and when pickier males pay a higher cost of preference...

..We show that this is the case when the combined forces of natural and sexual selection induce underdominance at the trait locus...

..However, the strength of selection on a modifier is less than the summed strengths had there been deleterious mutations only and advantageous mutations only...

..We conclude that asexual populations can gain most of the benefit of segregation through MR while avoiding the costs associated with sexual reproduction...

..We show that models of human history that include both population growth and spatial structure can generate the observed patterns without selection...

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..We review these experimental evolution studies and present new data on differences in maximal growth rate for cells of different ploidy levels...

..Interpreted in light of evolutionary theory, these studies rule out positive in these experiments epistasis as a major source of genetic associations. Further studies are needed, however, to tease apart other possible sources...

..Our methods allow for the direct estimation of the effect of a trait on speciation and extinction rates using incompletely resolved phylogenies...

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..Furthermore, ploidy level is itself a mutable trait in the presence of EMS, with both haploids and tetraploids often evolving towards diploidy (the ancestral state of S. cerevisiae) during the course of the experiment...

..These results are consistent with theory that predicts haploids should evolve faster than diploids at large population sizes...

..This result may help to explain otherwise puzzling phenomena such as why dichogamy is rarely complete in nature and why dichogamy tends to be associated with asynchronous flower presentation...

..In contrast, the evolution of plastic recombination in diploids is much more restricted. Selection on plasticity requires the ability to detect DNA damage or cis-trans effects as may occur through maternal effects on fitness...

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..In P. tremuloides, the per-locus per-year neutral somatic mutation rate across 14 microsatellite loci was estimated to lie between 6 x 10(-7) (lower bound) and 4 x 10(-5) (upper bound)...

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..34. This study reveals the potential of Ecotilling as a rapid genotype discovery method to explore and utilize the large pool of genetic variation in tree species...

..g., is the rate of speciation elevated for one character state over the other?). We demonstrate the application of the method using simulated data with known parameter values...

..As the vegetative life cycle of S. cerevisiae is predominantly diploid, this experiment provides evidence that genome size evolution is constrained, with selection favouring the genomic content typical of the yeast's evolutionary past...

..These results suggest the existence of a mitotic mechanism allowing the elimination of an entire set of chromosomes in S. cerevisiae, thereby reducing the ploidy level...

..Our models indicate that the evolution of SRA in nature should be strongly influenced by the genetic architecture of the traits on which it is based and the form of selection affecting them...

..We consider these results in light of human genetic data to infer how likely it is that such deleterious hitchhikers have occurred in our recent evolutionary past...

..We find that intermediate parasite migration rates maximize the degree of local adaptation of the parasite and lead to a higher ES recombination rate in the host...

..These results are consistent with the predominance of haploidy among parasitic protists...

..Our model provides testable predictions that can help interpret accumulating data on expression levels for genes relevant to host-parasite interactions...

..Thus to draw conclusions on the evolution of recombination from experimental data, it is necessary to consider the distribution of epistatic interactions together with the associated selection coefficients...

..This "abandon-ship" mechanism provides a plausible model for the evolution and maintenance of facultative sex...

..arenosa than in related diploid taxa but a near complete population bottleneck associated with the origins of A. suecica...

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..In cases where segregation and recombination act in opposite directions, we found that the effects of segregation dominate as an evolutionary force acting on sex in diploids...

..In some cases, particularly those where mating occurs within groups, we find that assortative mating evolves sufficiently to catalyze sympatric speciation in the interacting species...