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At least 433 records · Page 24Linked to original sources
PubMed1988

The alcohol dehydrogenase polymorphism in Drosophila melanogaster: fitness measurements and predictions under conditions with no alcohol stress.

The relative fitnesses of the different Adh genotypes under normal laboratory conditions and in the absence of alcohol stress were estimated in Drosophila melanogaster according to Prout's method. The larval component (viability) did not reveal fitness differences between the genotypes but for the adult component significant differences were observed. The female adult component (fecundity) showed an overdominant pattern: both homozygous genotypes showed a relative fitness significantly lower than the heterozygous genotype. For the male adult component (virility) also differences were observed. The homozygous SS genotype showed a lower relative fitness than the other two genotypes. Predictions for gene frequency changes based on the estimated fitness values do show a reasonably good correspondence with frequency changes actually observed in a number of experimental cage populations and indicate a globally stable equilibrium around a frequency of the F allele of 0.40-0.70. The relevance of these fitness estimates, obtained under conditions with no alcohol stress, for the explanation of the Adh polymorphisms observed in nature is discussed.

Alcohol Dehydrogenase↗
PubMed1989

The P-M and the 23.5 MRF (hobo) systems of hybrid dysgenesis in Drosophila melanogaster are independent of each other.

Strains of Drosophila melanogaster bearing the male recombination factor 23.5 MRF induce hybrid dysgenesis in a way which is highly reminiscent of the P-M system, and, most probably, causally related to the activity of the transposable element hobo. We have investigated potential interactions between the two systems of hybrid dysgenesis by studying mixed lines derived from bidirectional crosses between 23.5 MRF and P strains, and analyzed their potentials to induce or suppress the occurrence of dysgenesis. All new lines possess the P induction abilities, as determined by two different procedures, and have also acquired a P cytotype. In contrast, some of them lost their ability to induce the non-P-M dysgenesis, as well as to suppress the action of 23.5 MRF. This loss of the 23.5 MRF induction abilities parallels the selective loss of full-length hobo elements from the genome of these lines, providing further substantiation to the notion that the 23.5 MRF activity is directly linked to this transposable element.

Animals↗
PubMed1993

Selection and the evolution of genetic life cycles.

The evolution of haploid and diploid phases of the life cycle is investigated theoretically, using a model where the relative length of haploid and diploid phases is under genetic control. The model assumes that selection occurs in both phases and that fitness in each phase is a function of the time spent in that phase. The equilibrium and stability conditions that allow for all-haploid, all-diploid, or polyphasic life cycles are considered for general survivorship functions. Types of stable life cycles possible depend on the form of the viability selection. If mortality rates are constant, either haploidy or diploidy is the only stable life cycle possible. Departures from constant mortality can give qualitatively different results. For example, when survivorship in each phase is a linear, decreasing function of the time spent in the phase, stable haploid, diploid or polyphasic life cycles are possible. The addition of genetic variation at a coevolving viability locus does not qualitatively affect the outcome with respect to the maintenance of polyphasic cycles but can lead to situations where more than one life cycle is concurrently stable. These results show that trade-offs between the advantages of being diploid and of being haploid may help explain the patterns of life cycles found in nature and that the type of selection may be critical to determining the results.

Biological Evolution↗
PubMed1993

The effect of deleterious mutations on neutral molecular variation.

Selection against deleterious alleles maintained by mutation may cause a reduction in the amount of genetic variability at linked neutral sites. This is because a new neutral variant can only remain in a large population for a long period of time if it is maintained in gametes that are free of deleterious alleles, and hence are not destined for rapid elimination from the population by selection. Approximate formulas are derived for the reduction below classical neutral values resulting from such background selection against deleterious mutations, for the mean times to fixation and loss of new mutations, nucleotide site diversity, and number of segregating sites. These formulas apply to random-mating populations with no genetic recombination, and to populations reproducing exclusively asexually or by self-fertilization. For a given selection regime and mating system, the reduction is an exponential function of the total mutation rate to deleterious mutations for the section of the genome involved. Simulations show that the effect decreases rapidly with increasing recombination frequency or rate of outcrossing. The mean time to loss of new neutral mutations and the total number of segregating neutral sites are less sensitive to background selection than the other statistics, unless the population size is of the order of a hundred thousand or more. The stationary distribution of allele frequencies at the neutral sites is correspondingly skewed in favor of rare alleles, compared with the classical neutral result. Observed reductions in molecular variation in low recombination genomic regions of sufficiently large size, for instance in the centromere-proximal regions of Drosophila autosomes or in highly selfing plant populations, may be partly due to background selection against deleterious mutations.

Animals↗
PubMed2003

On the evolutionary advantage of fitness-associated recombination.

The adaptive value of recombination remains something of a puzzle. One of the basic problems is that recombination not only creates new and advantageous genetic combinations, but also breaks down existing good ones. A negative correlation between the fitness of an individual and its recombination rate would result in prolonged integrity of fitter genetic combinations while enabling less fit ones to produce new combinations. Such a correlation could be mediated by various factors, including stress responses, age, or direct DNA damage. For haploid population models, we show that an allele for such fitness-associated recombination (FAR) can spread both in asexual populations and in populations reproducing sexually at any uniform recombination rate. FAR also carries an advantage for the population as a whole, resulting in a higher average fitness at mutation-selection balance. These results are demonstrated in populations adapting to new environments as well as in well-adapted populations coping with deleterious mutations. Current experimental results providing evidence for the existence of FAR in nature are discussed.

Adaptation, Physiological↗
PubMed1985

The units of selection and measures of fitness.

This paper presents a unified account of the properties of the measures, Malthusian parameter and entropy in predicting evolutionary change in populations of macromolecules, cells and individuals. The Malthusian parameter describes the intrinsic rate of increase of the population. The entropy describes the intrinsic variability in populations: it characterizes the variability in mutation and replication rates in populations of macromolecules; the rate of decay of synchrony in populations of cells; and the degree of iteroparity in populations of individuals. The Malthusian parameter determines ultimate population numbers: under constant environmental conditions, it is the rate of increase when equilibrium conditions are attained. Entropy determines population stability: the gain in the Malthusian parameter due to small fluctuations in the life-cycle variables is determined by entropy. These properties, which are valid for populations of macromolecules, cells and individuals, show that the Malthusian parameter and entropy act as complimentary fitness indices in understanding evolutionary change in populations.

Biological Evolution↗
PubMed1996

Cooperation and conflict in the evolution of individuality. II. Conflict mediation.

Evolutionary transitions in the units of selection require the promotion of cooperation and the regulation of conflict among the lower level units. For multicellular organisms to emerge as a new unit of selection, the selfish tendencies of their component cells had to be controlled. Theoretical results indicate organisms may regulate this internal conflict and competition in several ways: by reducing the somatic mutation rate, by sequestering cells in a germ line and by directly reducing the benefits to cell of defecting.

Animals↗
PubMed2000

Genetic monogamy and biparental care in an externally fertilizing fish, the largemouth bass (Micropterus salmoides).

Breeding, male North American sunfish (Centrarchidae), are often brightly coloured and promiscuous. However, the largemouth bass (Micropterus salmoides) is sexually monomorphic in appearance and socially monogamous. Unlike some other nest-tending centrarchids in the genus Lepomis, largemouth bass have also been reported to provide biparental care to eggs and fry. Here we use microsatellite markers in order to test whether social monogamy predicts genetic monogamy in the largemouth bass. Offspring were collected from 26 nests each usually guarded by a pair of adults, many of which were also captured. Twenty-three of these progeny cohorts (88%) proved to be composed almost exclusively of full-sibs and were thus the product of monogamous matings. Cuckoldry by males was rare. The genetic data also revealed that some nests contain juveniles that were not the progeny of the guardian female, a finding that can be thought of as low-level 'female cuckoldry'. Overall, however, the data provide what may be the first genetic documentation of near-monogamy and biparental care in a vertebrate with external fertilization.

Animals↗
PubMed2002

The X chromosome is a hot spot for sexually antagonistic fitness variation.

Sexually antagonistic alleles are selected discordantly between the sexes. Experimental evidence indicates that sexually antagonistic fitness variation is abundant in the genome of Drosophila melanogaster. Theory predicts that the X chromosome will be enriched with this type of variation. To test this prediction in D. melanogaster, we sampled, and cytogenetically cloned, 20 X chromosomes and compared their fitness variation to genome-wide levels. At the juvenile stage, in which gender roles are most similar, the X chromosome made no detectable contribution to genome-wide fitness variation. At the adult stage, in which gender roles diverge, the X chromosome was estimated to harbour 45% of the genome-wide fitness variation and 97% of the genome-wide sexually antagonistic variation. This genomic structure has important implications for the process of sexual selection because X-linked sexually antagonistic variation contributes to negative intersexual heritability for fitness, i.e. high-fitness males (females) produce, on average, low-fitness daughters (sons).

Alleles↗