The role of natural selection in circadian behaviour: a molecular-genetic approach

Circadian rhythms (~24 h) in biochemistry, physiology and behaviour are found in almost all eukaryotes and some bacteria. The elucidation of the molecular components of the 24 h circadian clock in a number of model organisms in recent years has provided an opportunity to assess the adaptive value of variation in clock genes. Laboratory experiments using artificially generated mutants reveal that the circadian period is adaptive in a 24 h world. Natural genetic variation can also be studied, and there are a number of ways in which the signature of natural selection can be detected. These include the study of geographical patterns of genetic variation, which provide a first indication that selection may be at work, and the use of sophisticated statistical neutrality tests, which examine whether the pattern of variation observed is consistent with a selective rather than a neutral (or drift) scenario. Finally, examining the probable selective agents and their differential effects on the circadian phenotype of the natural variants provides the final compelling evidence for selection. We present some examples of how these types of analyses have not only enlightened the evolutionary study of clocks, but have also contributed to a more pragmatic molecular understanding of the function of clock proteins.

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Capacities for population-genetic variation and ecological adaptations

Genetika ◽

10.2298/gensr0702093m ◽

2007 ◽

Vol 39 (2) ◽

pp. 93-102 ◽

Cited By ~ 1

Author(s):

Dragoslav Marinkovic ◽

Vladimir Kekic

Keyword(s):

Genetic Variation ◽

Population Genetic ◽

Model Organisms ◽

Clear Cut ◽

Numerous Model ◽

Contemporary Science ◽

The Status ◽

Population Genetic Variation ◽

Two Parameters ◽

Almost All

In contemporary science of population genetics it is equally complex and important to visualize how adaptive limits of individual variation are determined, as well as to describe the amount and sort of this variation. Almost all century the scientists devoted their efforts to explain the principles and structure of biological variation (genetic, developmental, environmental, interactive, etc.), basing its maintenance within existing limits mostly on equilibria proclaimed by Hardy-Weinberg rules. Among numerous model-organisms that have been used to prove these rules and demonstrate new variants within mentioned concepts, Drosophila melanogaster is a kind of queen that is used in thousands of experiments for almost exactly 100 years (CARPENTER 1905), with which numerous discoveries and principles were determined that later turned out to be applicable to all other organisms. It is both, in nature and in laboratory, that Drosophilids were used to demonstrate the basic principles of population-genetic variation that was later applied to other species of animals. In ecological-genetic variation their richness in different environments could be used as an exact indicator of the status of a determined habitat, and its population-genetic structure may definitely point out to a possibility that specific resources of the environment start to be in danger to deteriorate, or to disappear in the near future. This paper shows clear-cut differences among environmental habitats, when populations of Drosophilidae are quantitatively observed in different wild, semi-domestic and domestic environments, demonstrating a highly expressed mutual dependence of these two parameters. A crucial approach is how to estimate the causes that determine the limits of biological, i.e. of individual and population-genetic variation. The realized, i.e. adaptive variation, is much lesser than a total possible variation of a polygenic trait, and in this study, using a moderately complex gene-enzyme system, is estimated to be smaller than 0.2%. For an allozymic system based on 9 loci at three D. melanogaster chromosomes, the estimate is that chromosomal types are reduced, on the average, to ca. 3% during meiotic divisions, and that available gene-enzyme combinations are reduced further 15 times in gamete selection. So finalized metabolic or adaptive developmental programs are emphasized to be the basic targets of Darwinian selection, rather than chromosomes or individual genes, that are involved in these programs.

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Faculty Opinions recommendation of Experimental evolution reveals natural selection on standing genetic variation.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.2772956.2439054 ◽

2010 ◽

Author(s):

John True ◽

Joseph Lachance

Keyword(s):

Genetic Variation ◽

Natural Selection ◽

Experimental Evolution

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POPULATION GENETICS OF ALLOZYME VARIATION IN NEUROSPORA INTERMEDIA

Genetics ◽

10.1093/genetics/80.4.785 ◽

1975 ◽

Vol 80 (4) ◽

pp. 785-805

Author(s):

P T Spieth

Keyword(s):

Genetic Variation ◽

Vegetative Reproduction ◽

Vascular Plant ◽

Natural Populations ◽

Allozyme Variation ◽

Regular Feature ◽

Local Populations ◽

Neurospora Intermedia ◽

Pattern Of Variation ◽

High Level

ABSTRACT Electrophoretically detectable variation in the fungus Neurospora intermedia has been surveyed among isolates from natural populations in Malaya, Papua, Australia and Florida. The principal result is a pattern of genetic variation within and between populations that is qualitatively no different than the well documented patterns for Drosophila and humans. In particular, there is a high level of genetic variation, the majority of which occurs at the level of local populations. Evidence is presented which argues that N. intermedia has a population structure analogous to that of an annual vascular plant with a high level of vegetative reproduction. Sexual reproduction appears to be a regular feature in the biology of the species. Substantial heterokaryon function seems unlikely in natural populations of N. intermedia. Theoretical considerations concerning the mechanisms underlying the observed pattern of variation most likely should be consistent with haploid selection theory. The implications of this constraint upon the theory are discussed in detail, leading to the presentation of a model based upon the concept of environmental heterogeneity. The essence of the model, which is equally applicable to haploid and diploid situations, is a shifting distribution of multiple adaptive niches among local populations such that a given population has a small net selective pressure in favor of one allele or another, depending upon its particular distribution of niches. Gene flow among neighboring populations with differing net selective pressures is postulated as the principal factor underlying intrapopulational allozyme variation.

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Inherited Differences in Crossing Over and Gene Conversion Frequencies Between Wild Strains of Sordaria fimicola From “Evolution Canyon”

Genetics ◽

10.1093/genetics/159.4.1573 ◽

2001 ◽

Vol 159 (4) ◽

pp. 1573-1593

Author(s):

Muhammad Saleem ◽

Bernard C Lamb ◽

Eviatar Nevo

Keyword(s):

Genetic Variation ◽

Gene Conversion ◽

Spontaneous Mutation ◽

Crossing Over ◽

Natural Genetic Variation ◽

Evolution Canyon ◽

Wild Strains ◽

Sordaria Fimicola ◽

First And Second Generation ◽

Consistent Direction

Abstract Recombination generates new combinations of existing genetic variation and therefore may be important in adaptation and evolution. We investigated whether there was natural genetic variation for recombination frequencies and whether any such variation was environment related and possibly adaptive. Crossing over and gene conversion frequencies often differed significantly in a consistent direction between wild strains of the fungus Sordaria fimicola isolated from a harsher or a milder microscale environment in “Evolution Canyon,” Israel. First- and second-generation descendants from selfing the original strains from the harsher, more variable, south-facing slope had higher frequencies of crossing over in locus-centromere intervals and of gene conversion than those from the lusher north-facing slopes. There were some significant differences between strains within slopes, but these were less marked than between slopes. Such inherited variation could provide a basis for natural selection for optimum recombination frequencies in each environment. There were no significant differences in meiotic hybrid DNA correction frequencies between strains from the different slopes. The conversion analysis was made using only conversions to wild type, because estimations of conversion to mutant were affected by a high frequency of spontaneous mutation. There was no polarized segregation of chromosomes at meiosis I or of chromatids at meiosis II.

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Variation in the morphology and flowering time of cluster clover (Trifolium glomeratum L.) and its relationship to distribution in southern Australia

Australian Journal of Agricultural Research ◽

10.1071/ar9951027 ◽

1995 ◽

Vol 46 (5) ◽

pp. 1027 ◽

Cited By ~ 14

Author(s):

FP Smith ◽

PS Cocks ◽

MA Ewing

Keyword(s):

Genetic Variation ◽

Flowering Time ◽

Seed Mass ◽

Annual Rainfall ◽

Strongly Correlated ◽

Summer Maximum ◽

Maximum Temperatures ◽

Pattern Of Variation ◽

Growth Habits

Cluster clover is a widely distributed and ecologically successful introduced legume in southern Australia. In an attempt to understand the role of genetic variation in this success, morphological and physiological traits were measured in 94 accessions from southern Australia and 6 from the Mediterranean basin. Flowering time ranged from 105 to 185 days after sowing, but was not strongly correlated with annual rainfall or length of growing season at the site of collection. Variation in other traits partitioned the populations into two morphs which, apart from flowering time and leaf marker, were largely homogeneous. The morphs differed significantly in floret number per inflorescence (22 v. 32-37) and seed mass (379 8g v. 523 8g), had different growth habits and strong within-morph associations between leaf markers and stipule and petal coloration. The morphs differed in their distributions within southern Australia and the pattern of distribution was related to summer maximum temperatures, winter minimum temperatures and spring rainfall. These results demonstrate that genetic variation has been important to the success of cluster clover and suggests that the variation is organized. The pattern of variation observed and its relationship to ecogeography is consistent with findings for other highly inbreeding species. A map of the species distribution in Western Australia is presented.

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Inherited and Environmentally Induced Differences in Mutation Frequencies Between Wild Strains of Sordaria fimicola From “Evolution Canyon”

Genetics ◽

10.1093/genetics/149.1.87 ◽

1998 ◽

Vol 149 (1) ◽

pp. 87-99

Author(s):

Bernard C Lamb ◽

Muhammad Saleem ◽

William Scott ◽

Nina Thapa ◽

Eviatar Nevo

Keyword(s):

Genetic Variation ◽

Spontaneous Mutation ◽

The South ◽

Natural Genetic Variation ◽

The North ◽

Ascospore Germination ◽

Evolution Canyon ◽

Two Generations ◽

Wild Strains ◽

Sordaria Fimicola

Abstract We have studied whether there is natural genetic variation for mutation frequencies, and whether any such variation is environment-related. Mutation frequencies differed significantly between wild strains of the fungus Sordaria fimicola isolated from a harsher or a milder microscale environment in “Evolution Canyon,” Israel. Strains from the harsher, drier, south-facing slope had higher frequencies of new spontaneous mutations and of accumulated mutations than strains from the milder, lusher, north-facing slope. Collective total mutation frequencies over many loci for ascospore pigmentation were 2.3, 3.5 and 4.4% for three strains from the south-facing slope, and 0.9, 1.1, 1.2, 1.3 and 1.3% for five strains from the north-facing slope. Some of this between-slope difference was inherited through two generations of selfing, with average spontaneous mutation frequencies of 1.9% for south-facing slope strains and 0.8% for north-facing slope strains. The remainder was caused by different frequencies of mutations arising in the original environments. There was also significant heritable genetic variation in mutation frequencies within slopes. Similar between-slope differences were found for ascospore germination-resistance to acriflavine, with much higher frequencies in strains from the south-facing slope. Such inherited variation provides a basis for natural selection for optimum mutation rates in each environment.

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Natural genetic variation drives microbiome selection in the Caenorhabditis elegans gut

Current Biology ◽

10.1016/j.cub.2021.04.046 ◽

2021 ◽

Author(s):

Fan Zhang ◽

Jessica L. Weckhorst ◽

Adrien Assié ◽

Ciara Hosea ◽

Christopher A. Ayoub ◽

...

Keyword(s):

Genetic Variation ◽

Caenorhabditis Elegans ◽

Natural Genetic Variation

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Cryptic variation and its manifestation in the Lower Trentonian Rafinesquina lineage (Ordovician, New York State)

The Paleontological Society Special Publications ◽

10.1017/s2475262200008522 ◽

1992 ◽

Vol 6 ◽

pp. 292-292

Author(s):

Robert Titus

Keyword(s):

New York ◽

Genetic Variation ◽

Natural Selection ◽

New York State ◽

Ecological Factors ◽

Stabilizing Selection ◽

Rapid Population Growth ◽

York State ◽

Cryptic Variation ◽

Adaptive Peak

Species populations commonly carry a great deal of genetic variation which is not expressed in individual phenotypes. Cryptic variation can be carried in recessive alleles, in cases of heterosis, or where modifier genes inhibit expression of the hidden trait. Other genetic and ecological factors also allow cryptic variation. Stabilizing selection prevents the expression of hidden traits; normalizing selection weeds out the deviants and canalizing selection suppresses their traits. Together the two keep the species near the top of the adaptive peak. Cryptic variation balances a species' need to be well-adapted to its environment and also for it to maintain a reserve of variation for potential environmental change. Expression of cryptic traits is rare and is usually associated with times of greatly reduced natural selection and rapid population growth, when the lower slopes of the adaptive peak are exposed.A possible example of the manifestation of cryptic traits occurs within the lower Trentonian Rafinesquina lineage of New York State. The two most commonly reported species of the genus have been reappraised in terms of cryptic variation. Extensive collections of Rafinesquina “lennoxensis” reveal far more intergrading morphotypes than had hitherto been recognized. The form which Salmon (1942) described is broadly U-shaped with sulcate margins. It grades into very convex forms as well as sharply-defined or convexly geniculate types. Of great importance, all forms grade into the flat, U-shaped, alate R. trentonensis, which is, by far, the most common and widespread lower Trentonian member of the genus. The R. “lennoxensis” assemblage has a very narrow biostratigraphy, being confined to a few locations in the upper Napanee Limestone. This places it in a quiet, protected, low stress, lagoonal setting behind the barrier shoal facies of the Kings Falls Limestone.The R. “lennoxensis” assemblage does not constitute a natural biologic species; it is reinterpreted as an assemblage of phenodeviants occupying a low stress, low natural selection lagoon facies. All such forms should be included within R. trentonensis. Given the evolutionary plasticity of this genus, extensive cryptic variation is not surprising.

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Evolution and evolvability: celebrating Darwin 200

Biology Letters ◽

10.1098/rsbl.2008.0639 ◽

2008 ◽

Vol 5 (1) ◽

pp. 44-46 ◽

Cited By ~ 33

Author(s):

John F.Y Brookfield

Keyword(s):

Genetic Variation ◽

Natural Selection ◽

Time Scales ◽

Evolutionary Change ◽

Adaptive Mutation ◽

Genetic Covariances ◽

The Relationship ◽

The Way

The concept of ‘evolvability’ is increasingly coming to dominate considerations of evolutionary change. There are, however, a number of different interpretations that have been put on the idea of evolvability, differing in the time scales over which the concept is applied. For some, evolvability characterizes the potential for future adaptive mutation and evolution. Others use evolvability to capture the nature of genetic variation as it exists in populations, particularly in terms of the genetic covariances between traits. In the latter use of the term, the applicability of the idea of evolvability as a measure of population's capacity to respond to natural selection rests on one, but not the only, view of the way in which we should envisage the process of natural selection. Perhaps the most potentially confusing aspects of the concept of evolvability are seen in the relationship between evolvability and robustness.

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