Outline • Selection On: – Overdominant Traits
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Polymorphism Under Apostatic
Heredity (1984), 53(3), 677—686 1984. The Genetical Society of Great Britain POLYMORPHISMUNDER APOSTATIC AND APOSEMATIC SELECTION VINTON THOMPSON Department of Biology, Roosevelt University, 430 South Michigan Avenue, Chicago, Illinois 60805 USA Received31 .i.84 SUMMARY Selection for warning colouration in well-defended species should lead to a single colour form in each local population, but some species are locally polymor- phic for aposematic colour forms. Single-locus two-allele models of frequency- dependent selection indicate that combined apostatic and aposematic selection may maintain stable polymorphism for one, two or three aposematic forms, provided that at least one form is subject to net apostatic selection. Frequency- independent selective differences between colour forms broaden the possibilities for aposematic polymorphism but lead to monomorphism if too large. Concurrent apostatic and aposematic selection may explain polymorphism for warning colouration in a number of jumping or moderately unpalatable insects. 1. INTRODUCTION Polymorphism for warning colouration poses a paradox for evolutionists because, as Fisher (1958) seems to have been the first to note, selection for warning colouration (aposematic selection) should lead to monomorphism. Under aposematic selection predators tend to avoid previously encountered phenotypes of undesirable prey, so that the fitness of each phenotype increases as it becomes more common. Given the presence of two forms, each will suffer at the hands of predators conditioned to avoid the other and one will eventually prevail because as soon as it gets the upper hand numerically it will drive the other to extinction. Nonetheless, many species are polymorphic for colour forms that appear to be aposematic. The ladybird beetles (Coccinellidae) furnish a number of particularly striking examples (Hodek, 1973; and see illustration in Ayala, 1978). -
Estimating Mutation Load in Human Genomes
HHS Public Access Author manuscript Author ManuscriptAuthor Manuscript Author Nat Rev Manuscript Author Genet. Author manuscript; Manuscript Author available in PMC 2016 July 25. Published in final edited form as: Nat Rev Genet. 2015 June ; 16(6): 333–343. doi:10.1038/nrg3931. Estimating Mutation Load in Human Genomes Brenna M. Henn1, Laura R. Botigué1, Carlos D. Bustamante2, Andrew G. Clark3, and Simon Gravel4 1Stony Brook University, SUNY, Department of Ecology and Evolution, 650 Life Sciences Building, Stony Brook, NY, 11794-5245 2Stanford University School of Medicine, Department of Genetics, 291 Campus Drive, Stanford, CA, 94305 3Cornell University, Department of Molecular Biology and Genetics, 526 Campus Road, Ithaca, NY, 14853-2703 4McGill University, Department of Human Genetics and Genome Quebec Innovation Centre, 740 Dr. Penfield Ave, Montreal, QC, H3A 0G1, Canada Abstract Next-generation sequencing technology has facilitated the discovery of millions of variants in human genomes. A sizeable fraction of these alleles are thought to be deleterious. We review the pattern of deleterious alleles as ascertained in genomic data and ask whether human populations differ in their predicted burden of deleterious alleles, a phenomenon known as “mutation load.” We discuss three demographic models that are predicted to affect mutation load and relate these models to the evidence (or the lack thereof) for variation in the efficacy of purifying selection in diverse human genomes. We also discuss why accurate estimation of mutation load depends on assumptions regarding the distribution of dominance and selection coefficients, quantities that are poorly characterized for current genomic datasets. Introduction The process of mutation constantly creates deleterious variation in a population. -
Epistasis and the Mutation Load: a Measurement-Theoretical Approach
Copyright 2001 by the Genetics Society of America Epistasis and the Mutation Load: A Measurement-Theoretical Approach Thomas F. Hansen and GuÈnter P. Wagner Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut 06520-8106 Manuscript received September 9, 2000 Accepted for publication February 15, 2001 ABSTRACT An approximate solution for the mean ®tness in mutation-selection balance with arbitrary order of epistatic interaction is derived. The solution is based on the assumptions of coupling equilibrium and that the interaction effects are multilinear. We ®nd that the effect of m-order epistatic interactions (i.e., interactions among groups of m loci) on the load is dependent on the total genomic mutation rate, U, to the mth power. Thus, higher-order gene interactions are potentially important if U is large and the interaction density among loci is not too low. The solution suggests that synergistic epistasis will decrease the mutation load and that variation in epistatic effects will elevate the load. Both of these results, however, are strictly true only if they refer to epistatic interaction strengths measured in the optimal genotype. If gene interactions are measured at mutation-selection equilibrium, only synergistic interactions among even numbers of genes will reduce the load. Odd-ordered synergistic interactions will then elevate the load. There is no systematic relationship between variation in epistasis and load at equilibrium. We argue that empirical estimates of gene interaction must pay attention to the genetic background in which the effects are measured and that it may be advantageous to refer to average interaction intensities as measured in mutation-selection equilibrium. -
THE MUTATION LOAD in SMALL POPULATIONS HE Mutation Load
THE MUTATION LOAD IN SMALL POPULATIONS MOT00 KIMURAZ, TAKE0 MARUYAMA, and JAMES F. CROW University of Wisconsin, Madison, Wisconsin Received April 29, 1963 HE mutation load has been defined as the proportion by which the population fitness, or any other attribute of interest, is altered by recurrent mutation (MORTON,CROW, and MULLER1956; CROW1958). HALDANE(1937) and MULLER(1950) had earlier shown that this load is largely independent of the harmfulness of the mutant. As long as the selective disadvantage of the mutant is of a larger order of magnitude than the mutation rate and the heterozygote fitness is not out of the range of that of the homozygotes, the load (measured in terms of fitness) is equal to the mutation rate for a recessive mutant and approxi- mately twice the mutation rate for a dominant mutant. A detailed calculation of the value for various degrees of dominance has been given by KIMURA(1 961 ) . In all these studies it has been assumed that the population is so large and the conditions so stable that the frequency of a mutant gene is exactly determined by the mutation rates, dominance, and selection coefficients, with no random fluctuation. However, actual populations are finite and also there are departures from equilibrium conditions because of variations in the various determining factors. Our purpose is to investigate the effect of random drift caused by a finite population number. It would be expected that the load would increase in a small population because the gene frequencies would drift away from the equilibrium values. This was confirmed by our mathematical investigations, but two somewhat unexpected results emerged. -
Signals of Predation-Induced Directional and Disruptive Selection in the Threespine Stickleback
Eawag_07048 Evolutionary Ecology Research, 2012, 14: 193–205 Signals of predation-induced directional and disruptive selection in the threespine stickleback Michael Zeller, Kay Lucek, Marcel P. Haesler, Ole Seehausen and Arjun Sivasundar Institute for Ecology and Evolution, University of Bern, Bern, Switzerland and Department of Fish Ecology, Eawag Centre for Ecology, Evolution and Biogeochemistry, Kastanienbaum, Switzerland ABSTRACT Background: Different predation regimes may exert divergent selection pressure on phenotypes and their associated genotypes. Threespine stickleback Gasterosteus aculeatus have a suite of bony structures, which have been shown to be an effective defence against predation and have a well-known genetic basis. Question: Do different predator regimes induce different selective pressures on growth rates and defence phenotypes in threespine stickleback between different habitats across distinct age classes? Hypothesis: In the presence of predation-induced selection, we expect diverging morphological responses between populations experiencing either low or high predation pressure. Study system: Threespine stickleback were sampled from two natural but recently established populations in an invasive range. One site has a high density of fish and insect predators, while at the other site predation pressure is low. Methods: We inferred predator-induced selection on defence traits by comparing the distribution of size classes, defence phenotypes, and an armour-related genotype between dif- ferent age classes in a high and a low predation regime. Results: Under high predation, there are indications of directional selection for faster growth, whereas lateral plate phenotypes and associated genotypes show indications for disruptive selection. Heterozygotes at the Eda-gene have a lower survival rate than either homozygote. Neither pattern is evident in the low predation regime. -
A Threefold Genetic Allee Effect: Population Size Affects Cross-Compatibility
Genetics: Published Articles Ahead of Print, published on February 3, 2005 as 10.1534/genetics.104.034553 A Threefold Genetic Allee Effect: Population Size Affects Cross-Compatibility, Inbreeding Depression, and Drift Load in the Self-Incompatible Ranunculus reptans Yvonne Willi,* Josh Van Buskirk,† Markus Fischer* ,1 * Institute of Environmental Sciences, University of Zürich, 8057 Zürich, Switzerland † Zoology Department, Melbourne University, Melbourne, VIC 3010, Australia 1 Institute of Biochemistry and Biology, University of Potsdam, 14471 Potsdam, Germany Y. Willi et al., page 2 Running head: INBREEDING DEPRESSION AND DRIFT LOAD Key words: Inbreeding load, fixed drift load, polyploidy, SI system, small population Corresponding author: Yvonne Willi Institut für Umweltwissenschaften Universität Zürich Winterthurerstrasse 190 CH-8057 Zürich, Switzerland telephone: ++ 41-1-635-4067 fax: ++ 41-1-635-5711 email: [email protected] Y. Willi et al. , page 3 ABSTRACT A decline in population size can lead to the loss of allelic variation, increased inbreeding, and the accumulation of genetic load through drift. We estimated the fitness consequences of these processes in offspring of controlled within-population crosses from 13 populations of the self-incompatible, clonal plant Ranunculus reptans. We used allozyme allelic richness as a proxy for long-term population size, which was positively correlated with current population size. Crosses between plants of smaller populations were less likely to be compatible. Inbreeding load, assessed as the slope of the relationship between offspring performance and parental kinship coefficients, was not related to population size, suggesting that deleterious mutations had not been purged from small populations. Offspring from smaller populations were on average more inbred, so inbreeding depression in clonal fitness was higher in small populations. -
Genetic Load in Sexual and Asexual Diploids: Segregation, Dominance and Genetic Drift
Copyright Ó 2007 by the Genetics Society of America DOI: 10.1534/genetics.107.073080 Genetic Load in Sexual and Asexual Diploids: Segregation, Dominance and Genetic Drift Christoph R. Haag1 and Denis Roze2 University of Edinburgh, Institute of Evolutionary Biology, Edinburgh EH9 3JT, United Kingdom Manuscript received March 8, 2007 Accepted for publication April 19, 2007 ABSTRACT In diploid organisms, sexual reproduction rearranges allelic combinations between loci (recombina- tion) as well as within loci (segregation). Several studies have analyzed the effect of segregation on the genetic load due to recurrent deleterious mutations, but considered infinite populations, thus neglecting the effects of genetic drift. Here, we use single-locus models to explore the combined effects of segrega- tion, selection, and drift. We find that, for partly recessive deleterious alleles, segregation affects both the deterministic component of the change in allele frequencies and the stochastic component due to drift. As a result, we find that the mutation load may be far greater in asexuals than in sexuals in finite and/or subdivided populations. In finite populations, this effect arises primarily because, in the absence of segregation, heterozygotes may reach high frequencies due to drift, while homozygotes are still efficiently selected against; this is not possible with segregation, as matings between heterozygotes constantly prod- uce new homozygotes. If deleterious alleles are partly, but not fully recessive, this causes an excess load in asexuals at intermediate population sizes. In subdivided populations without extinction, drift mostly occurs locally, which reduces the efficiency of selection in both sexuals and asexuals, but does not lead to global fixation. -
The Inflated Significance of Neutral Genetic Diversity in Conservation Genetics PERSPECTIVE Jo~Ao C
PERSPECTIVE The inflated significance of neutral genetic diversity in conservation genetics PERSPECTIVE Jo~ao C. Teixeiraa,b,1 and Christian D. Hubera,1 Edited by Andrew G. Clark, Cornell University, Ithaca, NY, and approved December 30, 2020 (received for review July 22, 2020) The current rate of species extinction is rapidly approaching unprecedented highs, and life on Earth presently faces a sixth mass extinction event driven by anthropogenic activity, climate change, and ecological collapse. The field of conservation genetics aims at preserving species by using their levels of genetic diversity, usually measured as neutral genome-wide diversity, as a barometer for evaluating pop- ulation health and extinction risk. A fundamental assumption is that higher levels of genetic diversity lead to an increase in fitness and long-term survival of a species. Here, we argue against the perceived impor- tance of neutral genetic diversity for the conservation of wild populations and species. We demonstrate that no simple general relationship exists between neutral genetic diversity and the risk of species extinc- tion. Instead, a better understanding of the properties of functional genetic diversity, demographic his- tory, and ecological relationships is necessary for developing and implementing effective conservation genetic strategies. conservation genetics | adaptive potential | inbreeding depression | genetic load | species extinction Are Species with Little Genetic Diversity Moreover, low genetic diversity is related to reduced Endangered? individual life span and health, along with a depleted Climate change caused by human activity is currently capacity for population growth (9). In contrast, high responsible for widespread ecological disruption and levels of genetic diversity are often seen as key to habitat destruction, with an ensuing unprecedented promoting population survival and guaranteeing the rate of species loss known as the Anthropocene Mass adaptive potential of natural populations in the face of Extinction (1–4). -
Population Dynamics of Underdominance Gene Drive Systems in Continuous Space
bioRxiv preprint doi: https://doi.org/10.1101/449355; this version posted October 22, 2018. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC 4.0 International license. Population dynamics of underdominance gene drive systems in continuous space Jackson Champer1,2*, Joanna Zhao1, Samuel E. Champer1, Jingxian Liu1, Philipp W. Messer1* 1Department of Biological Statistics anD Computational Biology, 2Department of Molecular Biology anD Genetics, Cornell University, Ithaca, NY 14853 *CorresponDing authors: JC ([email protected]), PWM ([email protected]) ABSTRACT UnDerDominance gene Drive systems promise a mechanism for rapiDly spreaDing payloaD alleles through a local population while otherwise remaining confineD, unable to spreaD into neighboring populations due to their frequency-dependent Dynamics. Such systems coulD proviDe a new tool in the fight against vector-borne diseases by disseminating transgenic payloads through vector populations. If local confinement can inDeeD be achieveD, the decision-making process for the release of such constructs woulD likely be consiDerably simpler compareD to other gene Drive mechanisms such as CRISPR homing drives. So far, the confinement ability of underdominance systems has only been demonstrated in moDels of panmictic populations linkeD by migration. How such systems woulD behave in realistic populations where individuals move over continuous space remains largely unknown. Here, we stuDy several underdominance systems in continuous-space population models and show that their dynamics are drastically altered from those in panmictic populations. Specifically, we find that all underdominance systems we stuDied can fail to persist in such environments, even after successful local establishment. -
Simulating Natural Selection in Landscape Genetics
Molecular Ecology Resources (2012) 12, 363–368 doi: 10.1111/j.1755-0998.2011.03075.x Simulating natural selection in landscape genetics E. L. LANDGUTH,* S. A. CUSHMAN† and N. A. JOHNSON‡ *Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA, †Rocky Mountain Research Station, United States Forest Service, Flagstaff, AZ 86001, USA, USA, ‡Department of Plant, Soil, and Insect Sciences and Graduate Program in Organismic and Evolutionary Biology, University of Massachusetts, Amherst, MA 01003, USA Abstract Linking landscape effects to key evolutionary processes through individual organism movement and natural selection is essential to provide a foundation for evolutionary landscape genetics. Of particular importance is determining how spa- tially-explicit, individual-based models differ from classic population genetics and evolutionary ecology models based on ideal panmictic populations in an allopatric setting in their predictions of population structure and frequency of fixation of adaptive alleles. We explore initial applications of a spatially-explicit, individual-based evolutionary landscape genetics program that incorporates all factors – mutation, gene flow, genetic drift and selection – that affect the frequency of an allele in a population. We incorporate natural selection by imposing differential survival rates defined by local relative fitness values on a landscape. Selection coefficients thus can vary not only for genotypes, but also in space as functions of local environmental variability. This simulator enables coupling of gene flow (governed by resistance surfaces), with natural selection (governed by selection surfaces). We validate the individual-based simulations under Wright-Fisher assumptions. We show that under isolation-by-distance processes, there are deviations in the rate of change and equilibrium values of allele frequency. -
“Visualizing Evolution As It Happens” Spatiotemporal Microbial Evolution on Antibiotic Landscapes Michael Baym, Tami D
“Visualizing evolution as it happens” Spatiotemporal microbial evolution on antibiotic landscapes Michael Baym, Tami D. Lieberman,*, Eric D. Kelsic, Remy Chait, Rotem Gross, Idan Yelin, Roy Kishony Science 09 Sep 2016 Strains grow in a branching-fashion, and time Sequencing of colonies at various lapse videos and genetic sequencing allow gradations allowed researchers to identify researchers to trace the ancestral “trees” of genes involved in conferring antibiotic resistant strains resistance, including many that were previously unknown Increasing antibiotic concentration Applications of the MEGA-Plate: 1. Mechanisms of antibiotic resistance 2. Analysis of spatial evolution Inoculation Is there any difference between adaptation fueled by standing genetic variation and adaptation fueled by new (de novo) mutations? 1 BACK TO THIS EQUATION… pq[ p(w w ) q(w w )] p AA Aa Aa aa w . We can see what happens with various types of selection by substituting explicit values for the fitnesses of the different genotypic classes. CASE 2: HETEROZYGOTE ADVANTAGE -- OVERDOMINANCE FITNESSES: WAA = 1 - s WAa = 1 Waa = 1 - t pq(sp tq) p 1 sp2 tq2 At equilibrium, p = t/(s+t). GENE FREQUENCIES WHEN THERE IS HETEROZYGOTE ADVANTAGE - OVERDOMINANCE FITNESSES: WAA = 1 - s WAa = 1 Waa = 1 - t .When s and t are negative there is overdominance and a stable equilibrium exists at: p = t / (s + t) 2 HETEROZYGOTE ADVANTAGE IN LAB POPULATIONS FITNESSES: Lethal allele VV VL LL 0.735 1.0 0 s = - 0.265 t = - 1.0 Viable allele pL = s/ (s + t) = - 0.265 / - 1.265 = 0.209 pv = t / (s + t) = - 1.0 / - 1.265 = 0.791 CASE STUDY: Heterozygote advantage . -
Genetic Load and Mortality in Partially Inbred Populations of Swine Barbara Jane Hicks Iowa State University
Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1967 Genetic load and mortality in partially inbred populations of swine Barbara Jane Hicks Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Agriculture Commons, and the Animal Sciences Commons Recommended Citation Hicks, Barbara Jane, "Genetic load and mortality in partially inbred populations of swine " (1967). Retrospective Theses and Dissertations. 3463. https://lib.dr.iastate.edu/rtd/3463 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. This dissertation has been microfilmed exactly as received 6 8-5957 HICKS, Barbara Jane, 1942- GENETIC LOAD AND MORTALITY IN PARTIALLY INBRED POPULATIONS OF SWINE. Iowa State University, Ph.D., 1967 Agriculture, animal culture University Microfilms, Inc., Ann Arbor, Michigan GENETIC LOAD Am MORTALITY IN PARTIALLY INBRED POPULATIONS OF SWINE "by Barbara Jane Hicks A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of The Requirements for the Degree of DOCTOR OF PHILOSOPHY Major Subject: Animal Breeding Approved: Signature was redacted for privacy. Signature was redacted for privacy. Heafâ of Major Department Signature was redacted for privacy. Iowa State University Of Science and Technology Ames, Iowa 1967 il TABLE OF CONTENTS Page INTRODUCTION 1 REVIEW OF LITERATURE 2 Genetic Load 2 Litter Size and Mortality l6 SOURCE OF DA.TA.