scholarly journals Testing evolutionary hypotheses about species borders: patterns of genetic variation towards the southern borders of two rainforest Drosophila and a related habitat generalist

2009 ◽  
Vol 276 (1661) ◽  
pp. 1517-1526 ◽  
Author(s):  
Belinda van Heerwaarden ◽  
Vanessa Kellermann ◽  
Michele Schiffer ◽  
Mark Blacket ◽  
Carla M Sgrò ◽  
...  
Keyword(s):  
Genetic Variation ◽  
Species Group ◽  
Starvation Resistance ◽  
Limited Evidence ◽  
Quantitative Genetic ◽  
Eastern Australia ◽  
Drosophila Serrata ◽  
Southern Border ◽  
Selection For ◽  
Habitat Generalist

Several evolutionary hypotheses help explain why only some species adapt readily to new conditions and expand distributions beyond borders, but there is limited evidence testing these hypotheses. In this study, we consider patterns of neutral (microsatellite) and quantitative genetic variation in traits in three species of Drosophila from the montium species group in eastern Australia. We found little support for restricted or asymmetrical gene flow in any species. In rainforest-restricted Drosophila birchii , there was evidence of selection for increased desiccation and starvation resistance towards the southern border, and a reduction in genetic diversity in desiccation resistance at this border. No such patterns existed for Drosophila bunnanda , which has an even more restricted distribution. In the habitat generalist Drosophila serrata , there was evidence for geographic selection for wing size and development time, although clinal patterns for increased cold and starvation resistance towards the southern border could not be differentiated from neutral expectations. These findings suggest that borders in these species are not limited by low overall genetic variation but instead in two of the species reflect patterns of selection and genetic variability in key traits limiting borders.

scholarly journals Joint Effects of Pleiotropic Selection and Stabilizing Selection on the Maintenance of Quantitative Genetic Variation at Mutation-Selection Balance

Genetics ◽  
2002 ◽  
Vol 162 (1) ◽  
pp. 459-471 ◽  
Author(s):  
Xu-Sheng Zhang ◽  
William G Hill
Keyword(s):  
Genetic Variation ◽  
Genetic Variance ◽  
Stabilizing Selection ◽  
Limited Impact ◽  
Quantitative Genetic ◽  
High Heritability ◽  
Selection For ◽  
Selection Parameters ◽  
Mutation And Selection ◽  
Polygenic Variation

AbstractIn quantitative genetics, there are two basic “conflicting” observations: abundant polygenic variation and strong stabilizing selection that should rapidly deplete that variation. This conflict, although having attracted much theoretical attention, still stands open. Two classes of model have been proposed: real stabilizing selection directly on the metric trait under study and apparent stabilizing selection caused solely by the deleterious pleiotropic side effects of mutations on fitness. Here these models are combined and the total stabilizing selection observed is assumed to derive simultaneously through these two different mechanisms. Mutations have effects on a metric trait and on fitness, and both effects vary continuously. The genetic variance (VG) and the observed strength of total stabilizing selection (Vs,t) are analyzed with a rare-alleles model. Both kinds of selection reduce VG but their roles in depleting it are not independent: The magnitude of pleiotropic selection depends on real stabilizing selection and such dependence is subject to the shape of the distributions of mutational effects. The genetic variation maintained thus depends on the kurtosis as well as the variance of mutational effects: All else being equal, VG increases with increasing leptokurtosis of mutational effects on fitness, while for a given distribution of mutational effects on fitness, VG decreases with increasing leptokurtosis of mutational effects on the trait. The VG and Vs,t are determined primarily by real stabilizing selection while pleiotropic effects, which can be large, have only a limited impact. This finding provides some promise that a high heritability can be explained under strong total stabilizing selection for what are regarded as typical values of mutation and selection parameters.

Selection for seed retention in Phalaris tuberosa L.

1963 ◽  
Vol 14 (6) ◽  
pp. 755 ◽  
Author(s):  
JR McWilliam
Keyword(s):  
Genetic Variation ◽  
Perennial Grass ◽  
Economic Problem ◽  
Base Population ◽  
Response To Selection ◽  
Seed Shattering ◽  
Commercial Strain ◽  
Seed Retention ◽  
Eastern Australia ◽  
Selection For

Loss of seed from the maturing inflorescence (seed shattering) is common in grasses and constitutes a serious economic problem in many species. This paper reports the results of artificial selection to improve seed retention in Phalaris tuberosa, an important perennial grass in south-eastern Australia. A study of the factors controlling the loss of seed in this species has revealed that the seed lies free within the inflorescence at maturity, and its loss is promoted by the opening of the glumes. This in turn is influenced by the structure of the inflorescence. The highest seed retention has been found in plants with a short rigid inflorescence containing a large number of densely packed spikelets. Wide variation for seed retention exists between strains of P. tuberosa. The lowest value (25%) was found for natural ecotypes from Algeria and Morocco, and the highest for a selection from a strain of the Australian commercial type obtained from Argentina (81%). An estimate of the heritability for seed retention was high (0.92 ± 0.11), and most of the genetic variation appeared to be additive. There was a marked response to selection for high seed retention. With the Argentine variety as the base population, an increase of 29% in the average level of seed retention was achieved from the first cycle of selection. This level represents an increase of 60% by comparison with the widely grown commercial strain. The importance of high seed retention in relation to the economics of Phalaris seed production is briefly discussed.

Maintenance of Quantitative Genetic Variation

2018 ◽  
Author(s):  
Bruce Walsh ◽  
Michael Lynch
Keyword(s):  
Genetic Variation ◽  
Quantitative Genetics ◽  
Stabilizing Selection ◽  
Quantitative Genetic ◽  
Wide Range

One of the major unresolved issues in quantitative genetics is what accounts for the amount of standing genetic variation in traits. A wide range of models, all reviewed in this chapter, have been proposed, but none fit the data, either giving too much variation or too little apparent stabilizing selection.

scholarly journals UNEQUAL CROSSING OVER AT THE rRNA TANDON AS A SOURCE OF QUANTITATIVE GENETIC VARIATION IN DROSOPHILA

Genetics ◽  
1980 ◽  
Vol 95 (3) ◽  
pp. 727-742 ◽  
Author(s):  
R Frankham ◽  
D A Briscoe ◽  
R K Nurthen
Keyword(s):  
Genetic Variation ◽  
Selection Response ◽  
Crossing Over ◽  
Wild Type ◽  
X Chromosomes ◽  
Unequal Crossing Over ◽  
Quantitative Genetic ◽  
Y Chromosomes ◽  
Homozygous Line ◽  
Minimum Estimate

ABSTRACT Abdominal bristle selection lines (three high and three low) and controls were founded from a marked homozygous line to measure the contribution of sex-linked "mutations" to selection response. Two of the low lines exhibited a period of rapid response to selection in females, but not in males. There were corresponding changes in female variance, in heritabilities in females, in the sex ratio (a deficiency of females) and in fitness, as well as the appearance of a mutant phenotype in females of one line. All of these changes were due to bb alleles (partial deficiencies for the rRNA tandon) in the X chromosomes of these lines, while the Y chromosomes remained wild-type bb+. We argue that the bb alleles arose by unequal crossing over in the rRNA tandon.—A prediction of this hypothesis is that further changes can occur in the rRNA tandon as selection is continued. This has now been shown to occur.—Our minimum estimate of the rate of occurrence of changes at the rRNA tandon is 3 × 10-4. As this is substantially higher than conventional mutation rates, the questions of the mechanisms and rates of origin of new quantitative genetic variation require careful re-examination.

scholarly journals The Molecular Basis of Quantitative Genetic Variation in Central and Secondary Metabolism in Arabidopsis

Genetics ◽  
1998 ◽  
Vol 149 (2) ◽  
pp. 739-747 ◽  
Author(s):  
Thomas Mitchell-Olds ◽  
Deana Pedersen
Keyword(s):  
Enzyme Activity ◽  
Genetic Variation ◽  
Secondary Metabolism ◽  
Genetic Correlations ◽  
Theoretical Models ◽  
Model Systems ◽  
Activity Levels ◽  
Significant Qtls ◽  
Cis Acting ◽  
Quantitative Genetic

Abstract To find the genes controlling quantitative variation, we need model systems where functional information on physiology, development, and gene regulation can guide evolutionary inferences. We mapped quantitative trait loci (QTLs) influencing quantitative levels of enzyme activity in primary and secondary metabolism in Arabidopsis. All 10 enzymes showed highly significant quantitative genetic variation. Strong positive genetic correlations were found among activity levels of 5 glycolytic enzymes, PGI, PGM, GPD, FBP, and G6P, suggesting that enzymes with closely related metabolic functions are coregulated. Significant QTLs were found influencing activity of most enzymes. Some enzyme activity QTLs mapped very close to known enzyme-encoding loci (e.g., hexokinase, PGI, and PGM). A hexokinase QTL is attributable to cis-acting regulatory variation at the AtHXK1 locus or a closely linked regulatory locus, rather than polypeptide sequence differences. We also found a QTL on chromosome IV that may be a joint regulator of GPD, PGI, and G6P activity. In addition, a QTL affecting PGM activity maps within 700 kb of the PGM-encoding locus. This QTL is predicted to alter starch biosynthesis by 3.4%, corresponding with theoretical models, suggesting that QTLs reflect pleiotropic effects of mutant alleles.

Genetic variation in fatty acid composition of subcutaneous fat in cattle

2013 ◽  
Vol 53 (2) ◽  
pp. 129 ◽  
Author(s):  
M. J. Kelly ◽  
R. K. Tume ◽  
S. Newman ◽  
J. M. Thompson
Keyword(s):  
Fatty Acids ◽  
Genetic Variation ◽  
Fatty Acid Composition ◽  
Fatty Acid ◽  
Acid Composition ◽  
Saturated Fatty Acids ◽  
Genetic Correlations ◽  
Subcutaneous Fat ◽  
Monounsaturated Fatty Acids ◽  
Selection For

Genetic parameters were estimated for fatty acid composition of subcutaneous beef fat of 1573 animals which were the progeny of 157 sires across seven breeds grown out on pasture and then finished on either grain or grass in northern New South Wales or in central Queensland. There was genetic variation in individual fatty acids with estimates of heritability for the proportions of C14 : 0, C14 : 1c9, C16 : 0, C16 : 1c9, C18 : 0 and C18 : 1c9 fatty acids in subcutaneous beef fat of the order of 0.4 or above. Also substantial correlations between some fatty acids were observed. Genetic correlations between fatty acids and fat depth at the P8 site suggested that much of the genetic variation in fatty acid composition was related to changes in fatness. Selection for decreased fatness resulted in decreased proportions of C18 : 1c9 with concomitant increases in C18 : 0, C14 : 0 and C16 : 0. This suggested that selection for decreased fatness at a given weight will result in a decrease in the proportions of monounsaturated fatty acids in the subcutaneous fat in the carcass with a corresponding increase in the proportions of saturated fatty acids.

Environmental stress and quantitative genetic variation in butterfly wing characteristics

2008 ◽  
Vol 23 (3) ◽  
pp. 473-485 ◽  
Author(s):  
W. Talloen ◽  
S. Van Dongen ◽  
H. Van Dyck ◽  
L. Lens
Keyword(s):  
Genetic Variation ◽  
Environmental Stress ◽  
Butterfly Wing ◽  
Quantitative Genetic
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