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PubMed1984

Artificial selection for a secondary sexual character in males of Drosophila silvestris from Hawaii.

Drosophila silvestris is endemic to the rain forests of Hawaii Island. In populations from the northeast side, the male foreleg tibia bears about 100 long cilia; these are used as a brush to stimulate the female during courtship. Cyclical family selection for high and low cilia number was carried out on progeny of lines started from single wild isofemales collected at a single site. Significant response in both directions was obtained; in the third generation the lines differed by a mean of 25 cilia. Despite much effort to save them, both lines died out without further advance; the low cilia number line died after five and the high cilia number line died after nine generations. The data are compatible with the view that the cilia character is polygenic and is maintained in nature by a stabilizing sexual selection that also favors a polygenic heterozygous state. Although selection in these experiments resulted in dysgenesis, such a result is not inevitable. Disorganization and reorganization of such a genetic system following a population bottleneck might be important as a predisposing condition for the emergence of a specifically novel and possibly isolating mode of courtship.

Journal Article↗
PubMed2000

Prediction, identification, and artificial selection of DNA rearrangements in Rhizobium: toward a natural genomic design.

Based on the DNA sequence of the symbiotic plasmid of Rhizobium strain NGR234, we predicted potential rearrangements generated by homologous recombination. All predicted rearrangements were identified experimentally by using a PCR-based methodology. Thus, the predicted and the actual dynamic maps of the replicon coincide. By using an approach that does not involve the introduction of exogenous genetic elements, derivative populations that are pure for specific rearrangements were obtained. We propose that knowledge of the DNA sequence of a genome offers the possibility of designing pathways of sequential rearrangements leading to alternative genomic structures. An experimental strategy to isolate bacterial populations containing the desired structures is discussed.

DNA, Bacterial↗
PubMed2006

Artificial selection on male longevity influences age-dependent reproductive effort in the black field cricket Teleogryllus commodus.

Although the trade-off between reproductive effort and longevity is central to both sexual selection and evolutionary theories of aging, there has been little synthesis between these fields. Here, we selected directly on adult longevity of male field crickets Teleogryllus commodus and measured the correlated responses of age-dependent male reproductive effort, female lifetime fecundity, and several other life-history traits. Male longevity responded significantly to five generations of divergent selection. Males from downward-selected lines commenced calling sooner and reached their peak calling effort at a younger age. They called more per night and, despite living less than half as long, called more overall than males selected for increased longevity. Females from the downward-selected lines lived significantly shorter lives than females from the upward-selected lines but still produced the same number of offspring. Nymph survival, development time, and body size and weight at eclosion did not show significant correlated response to selection on male longevity, despite evidence for substantial genetic variation in each of these traits. Collectively, our findings directly support the antagonistic pleiotropy model of aging and suggest an important role for sexual selection in the aging process.

Aging↗
PubMed1991

The response to artificial selection from new mutations in Drosophila melanogaster.

Twenty generations of divergent selection for abdominal bristle number were carried out starting from a completely homozygous population of Drosophila melanogaster. All lines were selected with the same proportion (20%) but at two different numbers of selected parents of each sex (5 or 25). A significant response to selection was detected in eight lines (out of 40) and, in most cases, it could be wholly attributed to a single mutation of relatively large effect (0.5-2 phenotypic standard deviations). The ratio of new mutational variance to environmental variance was estimated to be (0.33 +/- 0.11) X 10(-3). The distribution of mutant effects was asymmetrical, both with respect to bristle number (85% of it was negative) and to fitness (most detected bristle mutations were lethal or semilethal). Moreover, this distribution was leptokurtic, due to the presence of major genes. Gene action on bristles ranged from additive to completely recessive, no epistatic interactions being found. In agreement with theory, larger responses in each direction were achieved by those lines selected at greater effective population sizes. Furthermore, the observed divergence between lines selected in opposite directions was proportional to their effective size, as predicted for mutations of large effect.

Animals↗
PubMed1999

Improving the efficiency of artificial selection: more selection pressure with less inbreeding.

The use of population genetic variability in present-day selection schemes can be improved to reduce inbreeding rate and inbreeding depression without impairing genetic progress. We performed an experiment with Drosophila melanogaster to test mate selection, an optimizing method that uses linear programming to maximize the selection differential applied while at the same time respecting a restriction on the increase in inbreeding expected in the next generation. Previous studies about mate selection used computer simulation on simple additive genetic models, and no experiment with a real character in a real population had been carried out. After six selection generations, the optimized lines showed an increase in cumulated phenotypic selection differential of 10.76%, and at the same time, a reduction of 19.91 and 60.47% in inbreeding coefficient mean and variance, respectively. The increased selection pressure would bring greater selection response, and in fact, the observed change in the selected trait was on average 31.03% greater in the optimized lines. These improvements in the selection scheme were not made at the expense of the long-term expectations of genetic variability in the population, as these expectations were very similar for both mate selection and conventionally selected lines in our experiment.

Animals↗
PubMed1972

Genetic change of recombination value in Drosophila melanogaster. I. Artificial selection for high and low recombination and some properties of recombination-modifying genes.

A high and low selection line were formed by individual selection of females on the basis of their recombination. In the high line, recombination between Gl and Sb was increased from 14.8 percent to about 30 percent in twelve generations, when a plateau was apparently reached. Realized heritability was 0.12. The absence of a response to selection for low recombination is attributed mainly to genetic random drift, and partially to directional dominance and directional gene frequencies. Natural selection was found to act against increases of recombination above a level of about twenty percent in the measured interval. High recombination tended to be recessive to low recombination. In both selected lines and unselected stocks, intervals proximal to the centromere tended to have a higher recombination variance than distal intervals.

Animals↗
PubMedDate not supplied

The mode of evolution of molecular markers in populations of house mice under artificial selection for locomotor behavior.

A complete understanding of the mode of evolution of molecular markers is important for making inferences about different population genetic parameters, especially because a number of studies have reported patterns of allelic variation at molecular markers that are not in agreement with neutral evolutionary expectations. In the present study, house mice (Mus domesticus) from the fourteenth generation of a selection experiment for increased voluntary wheel-running activity were used to test how selection on a complex behavior affects the distribution of allelic variation by examining patterns of variation at six microsatellite and four allozyme loci. This population had a hierarchical structure that allowed for simultaneous testing of the effects of selection and genetic drift on the distribution of allelic variation by comparing observed patterns of allele frequencies and estimates of genetic divergence at multiple hierarchical levels to expectations under models of neutral evolution. The levels of genetic divergence among replicate lines and between selection groups, estimated from microsatellite data or pooled microsatellite and allozyme data, were not significantly different from expectations under neutral evolution. Furthermore, the pattern of change of allele frequencies between the base population and generation 14 was largely in agreement with expectations under neutral evolution (although the PGM locus exhibited a pattern of change within populations that was difficult to explain under neutral evolution). Overall the results generally provide support for the neutral evolution of molecular markers.

Animals↗
PubMed2002

ASPD (Artificially Selected Proteins/Peptides Database): a database of proteins and peptides evolved in vitro.

ASPD is a new curated database that incorporates data on full-length proteins, protein domains and peptides that were obtained through in vitro directed evolution processes (mainly by means of phage display). At present, the ASPD database contains data on 195 selection experiments, which were described in 112 original papers. For each experiment, the following information is given: (i) description of the target for binding, (ii) description of the protein or peptide which serves as the template for library construction and description of the native protein which binds the target, (iii) links to the major proteomic databases (SWISS-PROT, PDB, PROSITE and ENZYME), (iv) keywords referring to the biological significance of the experiment, (v) aligned sequences of proteins or peptides retrieved through in vitro evolution and relevant native or constructed sequences, (vi) the number of rounds of selection/amplification and (vii) the number of occurrences of clones with each sequence. The literature data include a full reference, a link to the MEDLINE database and the name of the corresponding author with his email address. ASPD has a user-friendly interface which allows for simple queries using the names of proteins and ligands, as well as keywords describing the biological role of the interaction studied, and also for queries based on authors' names. It is also possible to access the database by means of the SRS system, allowing complex queries. There is a BLAST search tool against the ASPD for looking directly for homologous sequences. Research tools of the ASPD allow the analysis of pairwise correlations in the sequences of proteins and peptides selected against one target. The URL for the ASPD database is http://www.sgi.sscc.ru/mgs/gnw/aspd/.

Animals↗
PubMedDate not supplied

Canalization at two extra scutellar bristles: artificial selection, chromosome analysis, and effect of temperature.

Two isofemale lines (P1 and P2) from a wild-type population of Drosophila melanogaster were selected for an invariant phenotype, two symmetrical and anterior scutellar extra bristles. Both P1 and P2 lines responded quickly to direct selection for two extra bristles, but although this phenotype was canalized in the P2 line, it was not in the P1 line. This lack of canalization at two extra bristles, measured by probit width, is the first reported in the literature. Analysis of chromosomal contribution showed the P1 decanalized phenotype to be due to chromosome 2. Synthetic chromosomal combinations were tested at four development temperatures (17 degrees, 21 degrees, 24 degrees, and 30 degrees C), and no correlation was observed between canalization at two extra bristles measured by probit width and minimum phenotypic change due to different temperatures. In this test, development at the highest temperatures was accompanied by an increased tendency to return to the wild phenotype in the canalized phenotypes only, suggesting that this drastic change could be accounted for by the action of the wild-type canalizing system. Decanalized genotypes, or those canalizing at phenotypes other than the wild type, could be explained by mutations which, to a greater or lesser degree, alter the normal genetic system of canalization.

Animals↗
PubMed2004

An attempt to artificially select Strongyloides ratti for resistance to the host immune response.

Previous work has selected Heligmosomoides polygyrus for increased survival and reproduction in hosts with prior exposure to H. polygyrus, and therefore 'immune' to this parasite. We investigated whether Strongyloides ratti would respond similarly to selection for survival and reproduction in S. ratti-immune hosts. During 32 generations of selection, there appeared to be an initial, brief response to this selection, but this was not sustained and, eventually, the immune-selected line died out. Specific measures of the response to selection at generations 6, 12 and 25 did not detect any significant response to selection. Therefore, we have failed to select a line of S. ratti for increased resistance to its host immune response.

Animals↗
PubMed1980

Evolution of canine information processing under conditions of natural and artificial selection.

The paper first argues that under conditions of domestication animals are necessarily selected (incidentally or otherwise) for (1) responsitivity to a broad band of stimuli and (2) behavioral plasticity. The consequent tractability of domestic animals is contrasted with the stimulus-boundness and response stereotypy of the fixed action patterns observed in wild animal behavior. It is suggested that this difference accounts for the differential trainability of wolves and dogs. The second section of the paper presents observational evidence that although capacity for observational learning. It is then noted that since observational learning requires recognition of means-ends relationships this conclusion is inconsistent with the claim that wolf behavior is largely instinct-bound. Finally, these conclusions are reconciled by hypothesizing that the wolf possesses a "duplex" information-processing system, a primitive "instinctual" system that mediates basic survival responses and a more recently acquired "cognitive" system that evolved as the wolf became a group hunter. Neurobehavioral and developmental comparisons of wolf and dog suggest that these two systems have become integrated into a single scheme in the course of the dog's domestication.

Animals↗
PubMed1986

The population genetics of Duchenne: natural and artificial selection in Duchenne muscular dystrophy.

The dynamics of X linkage was derived by Haldane in 1935. It is clear that the majority of mutations to an X linked lethal are new and that methods of control based on relatives of known cases can have limited impact on future incidence. The ability to define and track neighbouring loci allows some carriers who are daughters of carriers to be detected, and possible carriers to be excluded, with high reliability. Fetal diagnosis may also be made in the same way, but not without a substantial casualty rate. The precision of such diagnosis by proxy is limited both by the estimate of the recombination fraction and its variance, and can rarely exceed 1/s where the recombinational data are based on s informative meioses. Bracketing loci provide greater security from failure to diagnose cases but may involve substantial casualty rates. The estimation of both failure rates and casualty rates is discussed.

Female↗
PubMed2003

Artificial selection for high activity favors mighty mini-muscles in house mice.

After 14 generations of selection for voluntary wheel running, mice from the four replicate selected lines ran, on average, twice as many revolutions per day as those from the four unselected control lines. To examine whether the selected lines followed distinct strategies in the correlated responses of the size and metabolic capacities of the hindlimb muscles, we examined mice from selected lines, housed for 8 wk in cages with access to running wheels that were either free to rotate ("wheel access" group) or locked ("sedentary"). Thirteen of twenty individuals in one selected line (line 6) and two of twenty in another (line 3) showed a marked reduction ( approximately 50%) in total hindlimb muscle mass, consistent with the previously described expression of a small-muscle phenotype. Individuals with these "mini-muscles" were not significantly smaller in total body mass compared with line-mates with normal-sized muscles. Access to free wheels did not affect the relative mass of the mini-muscles, but did result in typical mammalian training effects for mitochondrial enzyme activities. Individuals with mini-muscles showed a higher mass-specific muscle aerobic capacity as revealed by the maximal in vitro rates of citrate synthase and cytochrome c oxidase. Moreover, these mice showed the highest activities of hexokinase and carnitine palmitoyl transferase. Females with mini-muscles showed the highest levels of phosphofructokinase, and males with mini-muscles the highest levels of pyruvate dehydrogenase. As shown by total muscle enzyme contents, the increase in mass-specific aerobic capacity almost completely compensated for the reduction caused by the "loss" of muscle mass. Moreover, the mini-muscle mice exhibited the lowest contents of lactate dehydrogenase and glycogen phosphorylase. Interestingly, metabolic capacities of mini-muscled mice resemble those of muscles after endurance training. Overall, our results demonstrate that during selection for voluntary wheel running, distinct adaptive paths that differentially exploit the genetic variation in morphological and physiological traits have been followed.

Animals↗