15,663 research outputs found
Exploring the effect of sex on empirical fitness landscapes
The nature of epistasis has important consequences for the evolutionary significance of sex and recombination. Recent efforts to find negative epistasis as a source of negative linkage disequilibrium and associated long-term advantage to sex have yielded little support. Sign epistasis, where the sign of the fitness effects of alleles varies across genetic backgrounds, is responsible for the ruggedness of the fitness landscape, with several unexplored implications for the evolution of sex. Here, we describe fitness landscapes for two sets of strains of the asexual fungus Aspergillus niger involving all combinations of five mutations. We find that 30% of the single-mutation fitness effects are positive despite their negative effect in the wild-type strain and that several local fitness maxima and minima are present. We then compare adaptation of sexual and asexual populations on these empirical fitness landscapes by using simulations. The results show a general disadvantage of sex on these rugged landscapes, caused by the breakdown by recombination of genotypes on fitness peaks. Sex facilitates movement to the global peak only for some parameter values on one landscape, indicating its dependence on the landscape’s topography. We discuss possible reasons for the discrepancy between our results and the reports of faster adaptation of sexual population
A solvable model of the evolutionary loop
A model for the evolution of a finite population in a rugged fitness
landscape is introduced and solved. The population is trapped in an
evolutionary loop, alternating periods of stasis to periods in which it
performs adaptive walks. The dependence of the average rarity of the population
(a quantity related to the fitness of the most adapted individual) and of the
duration of stases on population size and mutation rate is calculated.Comment: 6 pages, EuroLaTeX, 1 figur
Multidimensional epistasis and the transitory advantage of sex
Identifying and quantifying the benefits of sex and recombination is a long
standing problem in evolutionary theory. In particular, contradictory claims
have been made about the existence of a benefit of recombination on high
dimensional fitness landscapes in the presence of sign epistasis. Here we
present a comparative numerical study of sexual and asexual evolutionary
dynamics of haploids on tunably rugged model landscapes under strong selection,
paying special attention to the temporal development of the evolutionary
advantage of recombination and the link between population diversity and the
rate of adaptation. We show that the adaptive advantage of recombination on
static rugged landscapes is strictly transitory. At early times, an advantage
of recombination arises through the possibility to combine individually
occurring beneficial mutations, but this effect is reversed at longer times by
the much more efficient trapping of recombining populations at local fitness
peaks. These findings are explained by means of well established results for a
setup with only two loci. In accordance with the Red Queen hypothesis the
transitory advantage can be prolonged indefinitely in fluctuating environments,
and it is maximal when the environment fluctuates on the same time scale on
which trapping at local optima typically occurs.Comment: 34 pages, 9 figures and 8 supplementary figures; revised and final
versio
Deterministic and stochastic regimes of asexual evolution on rugged fitness landscapes
We study the adaptation dynamics of an initially maladapted asexual
population with genotypes represented by binary sequences of length . The
population evolves in a maximally rugged fitness landscape with a large number
of local optima. We find that whether the evolutionary trajectory is
deterministic or stochastic depends on the effective mutational distance
upto which the population can spread in genotype space. For
, the deterministic quasispecies theory operates while for
, the evolution is completely stochastic. Between these
two limiting cases, the dynamics are described by a local quasispecies theory
below a crossover time while above , the population
gets trapped at a local fitness peak and manages to find a better peak either
via stochastic tunneling or double mutations. In the stochastic regime
, we identify two subregimes associated with clonal
interference and uphill adaptive walks, respectively. We argue that our
findings are relevant to the interepretation of evolution experiments with
microbial populations.Comment: Revised version, to appear in Genetics. Note on the role of selection
in defining d_eff added; new figure 4 include
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