scholarly journals Large Genetic Change at Small Fatness Cost in Large Populations of Drosophila melanogaster Selected for Wind Tunnel Flight: Rethinking Fitness Surfaces

Genetics ◽  
1996 ◽  
Vol 144 (1) ◽  
pp. 205-213 ◽  
Author(s):  
K E Weber
Keyword(s):  
Drosophila Melanogaster ◽  
Wind Tunnel ◽  
Large Population ◽  
Genetic Change ◽  
Selected Lines ◽  
Term Change ◽  
Fitness Tests ◽  
Large Populations ◽  
Hybrid Lines

Abstract The fitness effects of extreme genetic change by selection were studied in large populations subjected to prolonged, intense selection. Two replicate populations of Drosophila melanogaster, with estimated effective sizes 500 ≥ Ne ≥ 1000, were selected for increased performance in a wind tunnel, selecting on average the fastest 4.5% of flies. The mean apparent flying speed of both lines increased from ~2 to 170 cm/sec and continued to respond at diminishing rates, without reaching a plateau, for 100 generations. Competitive fitness tests in generations 50 and 85 showed minimal or no fitness loss in selected lines compared to controls. Sublines relaxed in generations 65 and 85 showed minimal or no regression in apparent flying speed. Hybrid lines, from a cross of selected × control lines in generation 75, responded to reselection saltationally, showing that the chromosomes of the selected lines had been assembled from alleles at many loci, from many different chromosomes in the base population. Thus, major genetic change was achieved, but without the costs usually associated with strong directional selection. Large population size has been interpreted, in opposing models, as either a brake or an accelerator in its effects on long-term change by selection. These results favor the second model, and challenge the concept of rugged fitness surfaces underlying the first model.

A stabilizing interaction between the founder effect and interdeme mixing in competing populations of Drosophila melanogaster and Drosophila simulans

1972 ◽  
Vol 50 (3) ◽  
pp. 325-331 ◽  
Author(s):  
David L. Gibo
Keyword(s):  
Drosophila Melanogaster ◽  
Founder Effect ◽  
Large Population ◽  
Small Population ◽  
Large Populations ◽  
High Predation ◽  
Low Levels ◽  
Relationship Of ◽  
The Relationship ◽  
High Predation Pressure

Population cages with Drosophila melanogaster and D. simulans in competition were maintained under high predation pressure. The cages were established under three different conditions. One group of cages was started with a large population (150 adults) of each species. In these cages D. melanogaster was quickly depressed to low levels by D. simulans. A second group of cages was established with a small population (15 adults) of each species. These cages showed a great deal of diversity of both population size and dominant species. The third group of cages was established by mixing the populations of the cages of the second group and redistributing this mixed population among separate cages. In this last group of cages, the D. simulans population resembled those observed in the cages started with large populations, but the D. melanogaster populations had changed. Instead of being depressed to extinction, D. melanogaster was observed to maintain an apparently stable population. Interspecific competition between the two species appeared to have been reduced. The relationship of these results to the founder effect, interdeme mixing, and rapid changes in competitive relationships is discussed.

scholarly journals Long-term exhaustion of the inbreeding load in Drosophila melanogaster

Heredity ◽  
2021 ◽  
Author(s):  
Noelia Pérez-Pereira ◽  
Ramón Pouso ◽  
Ana Rus ◽  
Ana Vilas ◽  
Eugenio López-Cortegano ◽  
...  
Keyword(s):  
Inbreeding Depression ◽  
Evolutionary Biology ◽  
Gene Action ◽  
Large Population ◽  
Recessive Gene ◽  
Deleterious Alleles ◽  
Sib Mating ◽  
Large Populations ◽  
Great Relevance

AbstractInbreeding depression, the decline in fitness of inbred individuals, is a ubiquitous phenomenon of great relevance in evolutionary biology and in the fields of animal and plant breeding and conservation. Inbreeding depression is due to the expression of recessive deleterious alleles that are concealed in heterozygous state in noninbred individuals, the so-called inbreeding load. Genetic purging reduces inbreeding depression by removing these alleles when expressed in homozygosis due to inbreeding. It is generally thought that fast inbreeding (such as that generated by full-sib mating lines) removes only highly deleterious recessive alleles, while slow inbreeding can also remove mildly deleterious ones. However, a question remains regarding which proportion of the inbreeding load can be removed by purging under slow inbreeding in moderately large populations. We report results of two long-term slow inbreeding Drosophila experiments (125–234 generations), each using a large population and a number of derived lines with effective sizes about 1000 and 50, respectively. The inbreeding load was virtually exhausted after more than one hundred generations in large populations and between a few tens and over one hundred generations in the lines. This result is not expected from genetic drift alone, and is in agreement with the theoretical purging predictions. Computer simulations suggest that these results are consistent with a model of relatively few deleterious mutations of large homozygous effects and partially recessive gene action.

scholarly journals Polygenic mutation in Drosophila melanogaster: genetic analysis of selection lines.

Genetics ◽  
1995 ◽  
Vol 139 (3) ◽  
pp. 1293-1307 ◽  
Author(s):  
J D Fry ◽  
K A deRonde ◽  
T F Mackay
Keyword(s):  
Drosophila Melanogaster ◽  
Selection Line ◽  
Chromosomal Distribution ◽  
Biometric Analysis ◽  
Term Selection ◽  
Bristle Number ◽  
Parental Lines ◽  
Hybrid Lines ◽  
New Mutations

Abstract We have conducted genetic analyses of 12 long-term selection lines of Drosophila melanogaster derived from a highly inbred base population, containing new mutations affecting abdominal and sternopleural bristle number. Biometric analysis of the number of effective factors differentiating the selected lines from the base inbred indicated that with the exception of the three lines selected for increased number of abdominal bristles, three or more mutations contributed to the responses of the selection lines. Analysis of the chromosomal distribution of effects revealed that mutations affecting abdominal bristle number occurred on all three major chromosomes. In addition, Y-linked mutations with effects ranging from one to three bristles occurred in all three lines selected for decreased number of abdominal bristles, as well as in one line selected for increased abdominal bristle number. Mutations affecting sternopleural bristle number were mainly on the X and third chromosomes. One abdominal and one sternopleural selection line showed evidence of a segregating lethal with large effects on bristle number. As an indirect test for allelism of mutations occurring in different selection lines, the three lines selected in the same direction for the same trait were crossed in all possible combinations, and selection continued from the F2 hybrids. Responses of the hybrid lines usually did not exceed those of the most extreme parental lines, indicating that the responses of the parental lines may have been partly due to mutations at the same loci, although other interpretations are possible.

Vivid Imagers Are Better at Detecting Salient Changes

2006 ◽  
Vol 27 (4) ◽  
pp. 218-228 ◽  
Author(s):  
Paul Rodway ◽  
Karen Gillies ◽  
Astrid Schepman
Keyword(s):  
Individual Differences ◽  
Change Detection ◽  
Visual Imagery ◽  
Detection Task ◽  
Level Of Detail ◽  
Detection Accuracy ◽  
Change Detection Task ◽  
Term Change ◽  
High Level

This study examined whether individual differences in the vividness of visual imagery influenced performance on a novel long-term change detection task. Participants were presented with a sequence of pictures, with each picture and its title displayed for 17  s, and then presented with changed or unchanged versions of those pictures and asked to detect whether the picture had been changed. Cuing the retrieval of the picture's image, by presenting the picture's title before the arrival of the changed picture, facilitated change detection accuracy. This suggests that the retrieval of the picture's representation immunizes it against overwriting by the arrival of the changed picture. The high and low vividness participants did not differ in overall levels of change detection accuracy. However, in replication of Gur and Hilgard (1975) , high vividness participants were significantly more accurate at detecting salient changes to pictures compared to low vividness participants. The results suggest that vivid images are not characterised by a high level of detail and that vivid imagery enhances memory for the salient aspects of a scene but not all of the details of a scene. Possible causes of this difference, and how they may lead to an understanding of individual differences in change detection, are considered.

Social Cohesion, Breaks, and Transformations in Italy, 535–600

2018 ◽  
Author(s):  
Walter Pohl
Keyword(s):  
The Political ◽  
Late Antique ◽  
Religious Context ◽  
Ancient Society ◽  
Complex Process ◽  
Term Change ◽  
Two Generations ◽  
Classical Culture

When the Gothic War began in Italy in 535, the country still conserved many features of classical culture and late antique administration. Much of that was lost in the political upheavals of the following decades. Building on Chris Wickham’s work, this contribution sketches an integrated perspective of these changes, attempting to relate the contingency of events to the logic of long-term change, discussing political options in relation to military and economic means, and asking in what ways the erosion of consensus may be understood in a cultural and religious context. What was the role of military entrepreneurs of more or less barbarian or Roman extraction in the distribution or destruction of resources? How did Christianity contribute to the transformation of ancient society? The old model of barbarian invasions can contribute little to understanding this complex process. It is remarkable that for two generations, all political strategies in Italy ultimately failed.

Population fragmentation causes inadequate gene flow and increases extinction risk

2017 ◽  
Author(s):  
Richard Frankham ◽  
Jonathan D. Ballou ◽  
Katherine Ralls ◽  
Mark D. B. Eldridge ◽  
Michele R. Dudash ◽  
...  
Keyword(s):  
Gene Flow ◽  
Extinction Risk ◽  
Random Mating ◽  
Large Population ◽  
Isolated Population ◽  
Population Fragmentation ◽  
Single Population ◽  
Total Size ◽  
Limited Gene Flow

Most species now have fragmented distributions, often with adverse genetic consequences. The genetic impacts of population fragmentation depend critically upon gene flow among fragments and their effective sizes. Fragmentation with cessation of gene flow is highly harmful in the long term, leading to greater inbreeding, increased loss of genetic diversity, decreased likelihood of evolutionary adaptation and elevated extinction risk, when compared to a single population of the same total size. The consequences of fragmentation with limited gene flow typically lie between those for a large population with random mating and isolated population fragments with no gene flow.

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