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Berardi S, Rhodes JA, Berner MC, Greenblum SI, Bitter MC, Behrman EL, Betancourt NJ, Bergland AO, Petrov DA, Rajpurohit S, Schmidt P. Drosophila melanogaster pigmentation demonstrates adaptive phenotypic parallelism but genomic unpredictability over multiple timescales. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.08.09.607378. [PMID: 39211235 PMCID: PMC11361081 DOI: 10.1101/2024.08.09.607378] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/04/2024]
Abstract
Populations are capable of responding to environmental change over ecological timescales via adaptive tracking. However, the translation from patterns of allele frequency change to rapid adaptation of complex traits remains unresolved. We used abdominal pigmentation in Drosophila melanogaster as a model phenotype to address the nature, genetic architecture, and repeatability of rapid adaptation in the field. We show that D. melanogaster pigmentation evolves as a highly parallel and deterministic response to shared environmental gradients across latitude and season in natural North American populations. We then experimentally evolved replicate, genetically diverse fly populations in field mesocosms to remove any confounding effects of demography and/or cryptic structure that may drive patterns in wild populations; we show that pigmentation rapidly responds, in parallel, in fewer than ten generations. Thus, pigmentation evolves concordantly in response to spatial and temporal climatic gradients. We next examined whether phenotypic differentiation was associated with allele frequency change at loci with established links to genetic variance in pigmentation in natural populations. We found that across all spatial and temporal scales, phenotypic patterns were associated with variation at pigmentation-related loci, and the sets of genes we identified in each context were largely nonoverlapping. Therefore, our findings suggest that parallel phenotypic evolution is associated with an unpredictable genomic response, with distinct components of the polygenic architecture shifting across each environmental gradient to produce redundant adaptive patterns. Significance Statement Shifts in global climate conditions have heightened our need to understand the dynamics and pace of adaptation in natural populations. In order to anticipate the population-level response to rapidly changing environmental conditions, we need to understand whether trait evolution is predictable over short timescales, and whether the genetic basis of adaptation is shared or distinct across multiple timescales. Here, we explored parallelism in the adaptive response of a complex phenotype, D. melanogaster pigmentation, to shared conditions that varied over multiple spatiotemporal scales. Our results demonstrate that while phenotypic adaptation proceeds as a predictable response to environmental gradients, even over short timescales, the genetic basis of the adaptive response is variable and nuanced across spatial and temporal contexts.
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Alkan C, Brésard G, Frézal L, Richaud A, Ruaud A, Zhang G, Félix MA. Natural variation in infection specificity of Caenorhabditis briggsae isolates by two RNA viruses. PLoS Pathog 2024; 20:e1012259. [PMID: 38861582 PMCID: PMC11195985 DOI: 10.1371/journal.ppat.1012259] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2024] [Revised: 06/24/2024] [Accepted: 05/14/2024] [Indexed: 06/13/2024] Open
Abstract
Antagonistic relationships such as host-virus interactions potentially lead to rapid evolution and specificity in interactions. The Orsay virus is so far the only horizontal virus naturally infecting the nematode C. elegans. In contrast, several related RNA viruses infect its congener C. briggsae, including Santeuil (SANTV) and Le Blanc (LEBV) viruses. Here we focus on the host's intraspecific variation in sensitivity to these two intestinal viruses. Many temperate-origin C. briggsae strains, including JU1264 and JU1498, are sensitive to both, while many tropical strains, such as AF16, are resistant to both. Interestingly, some C. briggsae strains exhibit a specific resistance, such as the HK104 strain, specifically resistant to LEBV. The viral sensitivity pattern matches the strains' geographic and genomic relationships. The heavily infected strains mount a seemingly normal small RNA response that is insufficient to suppress viral infection, while the resistant strains show no small RNA response, suggesting an early block in viral entry or replication. We use a genetic approach from the host side to map genomic regions participating in viral resistance polymorphisms. Using Advanced Intercrossed Recombinant Inbred Lines (RILs) between virus-resistant AF16 and SANTV-sensitive HK104, we detect Quantitative Trait Loci (QTLs) on chromosomes IV and III. Building RILs between virus-sensitive JU1498 and LEBV-resistant HK104 followed by bulk segregant analysis, we identify a chromosome II QTL. In both cases, further introgressions of the regions confirmed the QTLs. This diversity provides an avenue for studying virus entry, replication, and exit mechanisms, as well as host-virus specificity and the host response to a specific virus infection.
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Affiliation(s)
- Cigdem Alkan
- IBENS, Department of Biology, Ecole Normale Supérieure, CNRS, Inserm, PSL Research University, Paris, France
| | - Gautier Brésard
- IBENS, Department of Biology, Ecole Normale Supérieure, CNRS, Inserm, PSL Research University, Paris, France
| | - Lise Frézal
- IBENS, Department of Biology, Ecole Normale Supérieure, CNRS, Inserm, PSL Research University, Paris, France
- Institut Pasteur, Université Paris Cité, Unité des Bactéries pathogènes entériques Paris, Paris, France
| | - Aurélien Richaud
- IBENS, Department of Biology, Ecole Normale Supérieure, CNRS, Inserm, PSL Research University, Paris, France
| | - Albane Ruaud
- IBENS, Department of Biology, Ecole Normale Supérieure, CNRS, Inserm, PSL Research University, Paris, France
| | - Gaotian Zhang
- IBENS, Department of Biology, Ecole Normale Supérieure, CNRS, Inserm, PSL Research University, Paris, France
| | - Marie-Anne Félix
- IBENS, Department of Biology, Ecole Normale Supérieure, CNRS, Inserm, PSL Research University, Paris, France
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Zhang MJ, Durvasula A, Chiang C, Koch EM, Strober BJ, Shi H, Barton AR, Kim SS, Weissbrod O, Loh PR, Gazal S, Sunyaev S, Price AL. Pervasive correlations between causal disease effects of proximal SNPs vary with functional annotations and implicate stabilizing selection. RESEARCH SQUARE 2023:rs.3.rs-3707248. [PMID: 38168385 PMCID: PMC10760228 DOI: 10.21203/rs.3.rs-3707248/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2024]
Abstract
The genetic architecture of human diseases and complex traits has been extensively studied, but little is known about the relationship of causal disease effect sizes between proximal SNPs, which have largely been assumed to be independent. We introduce a new method, LD SNP-pair effect correlation regression (LDSPEC), to estimate the correlation of causal disease effect sizes of derived alleles between proximal SNPs, depending on their allele frequencies, LD, and functional annotations; LDSPEC produced robust estimates in simulations across various genetic architectures. We applied LDSPEC to 70 diseases and complex traits from the UK Biobank (average N=306K), meta-analyzing results across diseases/traits. We detected significantly nonzero effect correlations for proximal SNP pairs (e.g., -0.37±0.09 for low-frequency positive-LD 0-100bp SNP pairs) that decayed with distance (e.g., -0.07±0.01 for low-frequency positive-LD 1-10kb), varied with allele frequency (e.g., -0.15±0.04 for common positive-LD 0-100bp), and varied with LD between SNPs (e.g., +0.12±0.05 for common negative-LD 0-100bp) (because we consider derived alleles, positive-LD and negative-LD SNP pairs may yield very different results). We further determined that SNP pairs with shared functions had stronger effect correlations that spanned longer genomic distances, e.g., -0.37±0.08 for low-frequency positive-LD same-gene promoter SNP pairs (average genomic distance of 47kb (due to alternative splicing)) and -0.32±0.04 for low-frequency positive-LD H3K27ac 0-1kb SNP pairs. Consequently, SNP-heritability estimates were substantially smaller than estimates of the sum of causal effect size variances across all SNPs (ratio of 0.87±0.02 across diseases/traits), particularly for certain functional annotations (e.g., 0.78±0.01 for common Super enhancer SNPs)-even though these quantities are widely assumed to be equal. We recapitulated our findings via forward simulations with an evolutionary model involving stabilizing selection, implicating the action of linkage masking, whereby haplotypes containing linked SNPs with opposite effects on disease have reduced effects on fitness and escape negative selection.
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Affiliation(s)
- Martin Jinye Zhang
- Ray and Stephanie Lane Computational Biology Department, School of Computer Science, Carnegie Mellon University, Pittsburgh, PA, USA
- Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, MA, USA
| | - Arun Durvasula
- Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, MA, USA
- Center for Genetic Epidemiology, Department of Population and Public Health Sciences, Keck School of Medicine, University of Southern California
| | - Colby Chiang
- Department of Pediatrics, Division of Genetics and Genomics, Boston Children’s Hospital, Boston, MA
| | - Evan M. Koch
- Department of Biomedical Informatics, Harvard Medical School, Boston, MA, USA
- Division of Genetics, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA, USA
| | - Benjamin J. Strober
- Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA
| | - Huwenbo Shi
- Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA
| | - Alison R. Barton
- Department of Human Evolutionary Biology, Harvard University, Cambridge, Massachusetts, United States of America
| | - Samuel S. Kim
- Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA
| | - Omer Weissbrod
- Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA
| | - Po-Ru Loh
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, MA, USA
- Division of Genetics, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA, USA
| | - Steven Gazal
- Center for Genetic Epidemiology, Department of Population and Public Health Sciences, Keck School of Medicine, University of Southern California
- Department of Quantitative and Computational Biology, University of Southern California
- Norris Comprehensive Cancer Center, Keck School of Medicine, University of Southern California
| | - Shamil Sunyaev
- Department of Biomedical Informatics, Harvard Medical School, Boston, MA, USA
- Division of Genetics, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA, USA
| | - Alkes L. Price
- Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, MA, USA
- Department of Biostatistics, Harvard T.H. Chan School of Public Health, Boston, MA, USA
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4
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Zhang MJ, Durvasula A, Chiang C, Koch EM, Strober BJ, Shi H, Barton AR, Kim SS, Weissbrod O, Loh PR, Gazal S, Sunyaev S, Price AL. Pervasive correlations between causal disease effects of proximal SNPs vary with functional annotations and implicate stabilizing selection. MEDRXIV : THE PREPRINT SERVER FOR HEALTH SCIENCES 2023:2023.12.04.23299391. [PMID: 38106023 PMCID: PMC10723494 DOI: 10.1101/2023.12.04.23299391] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2023]
Abstract
The genetic architecture of human diseases and complex traits has been extensively studied, but little is known about the relationship of causal disease effect sizes between proximal SNPs, which have largely been assumed to be independent. We introduce a new method, LD SNP-pair effect correlation regression (LDSPEC), to estimate the correlation of causal disease effect sizes of derived alleles between proximal SNPs, depending on their allele frequencies, LD, and functional annotations; LDSPEC produced robust estimates in simulations across various genetic architectures. We applied LDSPEC to 70 diseases and complex traits from the UK Biobank (average N=306K), meta-analyzing results across diseases/traits. We detected significantly nonzero effect correlations for proximal SNP pairs (e.g., -0.37±0.09 for low-frequency positive-LD 0-100bp SNP pairs) that decayed with distance (e.g., -0.07±0.01 for low-frequency positive-LD 1-10kb), varied with allele frequency (e.g., -0.15±0.04 for common positive-LD 0-100bp), and varied with LD between SNPs (e.g., +0.12±0.05 for common negative-LD 0-100bp) (because we consider derived alleles, positive-LD and negative-LD SNP pairs may yield very different results). We further determined that SNP pairs with shared functions had stronger effect correlations that spanned longer genomic distances, e.g., -0.37±0.08 for low-frequency positive-LD same-gene promoter SNP pairs (average genomic distance of 47kb (due to alternative splicing)) and -0.32±0.04 for low-frequency positive-LD H3K27ac 0-1kb SNP pairs. Consequently, SNP-heritability estimates were substantially smaller than estimates of the sum of causal effect size variances across all SNPs (ratio of 0.87±0.02 across diseases/traits), particularly for certain functional annotations (e.g., 0.78±0.01 for common Super enhancer SNPs)-even though these quantities are widely assumed to be equal. We recapitulated our findings via forward simulations with an evolutionary model involving stabilizing selection, implicating the action of linkage masking, whereby haplotypes containing linked SNPs with opposite effects on disease have reduced effects on fitness and escape negative selection.
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Affiliation(s)
- Martin Jinye Zhang
- Ray and Stephanie Lane Computational Biology Department, School of Computer Science, Carnegie Mellon University, Pittsburgh, PA, USA
- Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, MA, USA
| | - Arun Durvasula
- Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, MA, USA
- Center for Genetic Epidemiology, Department of Population and Public Health Sciences, Keck School of Medicine, University of Southern California
| | - Colby Chiang
- Department of Pediatrics, Division of Genetics and Genomics, Boston Children's Hospital, Boston, MA
| | - Evan M Koch
- Department of Biomedical Informatics, Harvard Medical School, Boston, MA, USA
- Division of Genetics, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA
| | - Benjamin J Strober
- Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA
| | - Huwenbo Shi
- Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA
| | - Alison R Barton
- Department of Human Evolutionary Biology, Harvard University, Cambridge, Massachusetts, United States of America
| | - Samuel S Kim
- Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA
| | - Omer Weissbrod
- Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA
| | - Po-Ru Loh
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, MA, USA
- Division of Genetics, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA
| | - Steven Gazal
- Center for Genetic Epidemiology, Department of Population and Public Health Sciences, Keck School of Medicine, University of Southern California
- Department of Quantitative and Computational Biology, University of Southern California
- Norris Comprehensive Cancer Center, Keck School of Medicine, University of Southern California
| | - Shamil Sunyaev
- Department of Biomedical Informatics, Harvard Medical School, Boston, MA, USA
- Division of Genetics, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA
| | - Alkes L Price
- Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, MA, USA
- Department of Biostatistics, Harvard T.H. Chan School of Public Health, Boston, MA, USA
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5
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Fausett SR, Sandjak A, Billard B, Braendle C. Higher-order epistasis shapes natural variation in germ stem cell niche activity. Nat Commun 2023; 14:2824. [PMID: 37198172 DOI: 10.1038/s41467-023-38527-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2022] [Accepted: 05/05/2023] [Indexed: 05/19/2023] Open
Abstract
To study how natural allelic variation explains quantitative developmental system variation, we characterized natural differences in germ stem cell niche activity, measured as progenitor zone (PZ) size, between two Caenorhabditis elegans isolates. Linkage mapping yielded candidate loci on chromosomes II and V, and we found that the isolate with a smaller PZ size harbours a 148 bp promoter deletion in the Notch ligand, lag-2/Delta, a central signal promoting germ stem cell fate. As predicted, introducing this deletion into the isolate with a large PZ resulted in a smaller PZ size. Unexpectedly, restoring the deleted ancestral sequence in the isolate with a smaller PZ did not increase-but instead further reduced-PZ size. These seemingly contradictory phenotypic effects are explained by epistatic interactions between the lag-2/Delta promoter, the chromosome II locus, and additional background loci. These results provide first insights into the quantitative genetic architecture regulating an animal stem cell system.
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Affiliation(s)
- Sarah R Fausett
- Université Côte d'Azur, CNRS, Inserm, IBV, Nice, France.
- Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, NC, USA.
| | - Asma Sandjak
- Université Côte d'Azur, CNRS, Inserm, IBV, Nice, France
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6
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Nyaanga J, Andersen EC. Linkage mapping reveals loci that underlie differences in Caenorhabditis elegans growth. G3 GENES|GENOMES|GENETICS 2022; 12:6663991. [PMID: 35961034 PMCID: PMC9526057 DOI: 10.1093/g3journal/jkac207] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Accepted: 08/05/2022] [Indexed: 11/12/2022]
Abstract
Abstract
Growth rate and body size are complex traits that contribute to the fitness of organisms. The identification of loci that underlie differences in these traits provides insights into the genetic contributions to development. Leveraging Caenorhabditis elegans as a tractable metazoan model for quantitative genetics, we can identify genomic regions that underlie differences in growth. We measured postembryonic growth of the laboratory-adapted wild-type strain (N2) and a wild strain from Hawaii (CB4856) and found differences in body size. Using linkage mapping, we identified three distinct quantitative trait loci (QTL) on chromosomes IV, V, and X that are associated with variation in body growth. We further examined these growth-associated quantitative trait loci using chromosome substitution strains and near-isogenic lines and validated the chromosome X quantitative trait loci. In addition, we generated a list of candidate genes for the chromosome X quantitative trait loci. These genes could potentially contribute to differences in animal growth and should be evaluated in subsequent studies. Our work reveals the genetic architecture underlying animal growth variation and highlights the genetic complexity of growth in Caenorhabditis elegans natural populations.
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Affiliation(s)
- Joy Nyaanga
- Department of Molecular Biosciences, Northwestern University , Evanston, IL 60208, USA
- Interdisciplinary Biological Sciences Program, Northwestern University , Evanston, IL 60208, USA
| | - Erik C Andersen
- Department of Molecular Biosciences, Northwestern University , Evanston, IL 60208, USA
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7
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Gene regulation in Escherichia coli is commonly selected for both high plasticity and low noise. Nat Ecol Evol 2022; 6:1165-1179. [PMID: 35726087 DOI: 10.1038/s41559-022-01783-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2021] [Accepted: 05/03/2022] [Indexed: 11/08/2022]
Abstract
Bacteria often respond to dynamically changing environments by regulating gene expression. Despite this regulation being critically important for growth and survival, little is known about how selection shapes gene regulation in natural populations. To better understand the role natural selection plays in shaping bacterial gene regulation, here we compare differences in the regulatory behaviour of naturally segregating promoter variants from Escherichia coli (which have been subject to natural selection) to randomly mutated promoter variants (which have never been exposed to natural selection). We quantify gene expression phenotypes (expression level, plasticity and noise) for hundreds of promoter variants across multiple environments and show that segregating promoter variants are enriched for mutations with minimal effects on expression level. In many promoters, we infer that there is strong selection to maintain high levels of plasticity, and direct selection to decrease or increase cell-to-cell variability in expression. Taken together, these results expand our knowledge of how gene regulation is affected by natural selection and highlight the power of comparing naturally segregating polymorphisms to de novo random mutations to quantify the action of selection.
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8
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Adams PE, Crist AB, Young EM, Willis JH, Phillips PC, Fierst JL. Slow Recovery from Inbreeding Depression Generated by the Complex Genetic Architecture of Segregating Deleterious Mutations. Mol Biol Evol 2022; 39:msab330. [PMID: 34791426 PMCID: PMC8789292 DOI: 10.1093/molbev/msab330] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The deleterious effects of inbreeding have been of extreme importance to evolutionary biology, but it has been difficult to characterize the complex interactions between genetic constraints and selection that lead to fitness loss and recovery after inbreeding. Haploid organisms and selfing organisms like the nematode Caenorhabditis elegans are capable of rapid recovery from the fixation of novel deleterious mutation; however, the potential for recovery and genomic consequences of inbreeding in diploid, outcrossing organisms are not well understood. We sought to answer two questions: 1) Can a diploid, outcrossing population recover from inbreeding via standing genetic variation and new mutation? and 2) How does allelic diversity change during recovery? We inbred C. remanei, an outcrossing relative of C. elegans, through brother-sister mating for 30 generations followed by recovery at large population size. Inbreeding reduced fitness but, surprisingly, recovery from inbreeding at large populations sizes generated only very moderate fitness recovery after 300 generations. We found that 65% of ancestral single nucleotide polymorphisms (SNPs) were fixed in the inbred population, far fewer than the theoretical expectation of ∼99%. Under recovery, 36 SNPs across 30 genes involved in alimentary, muscular, nervous, and reproductive systems changed reproducibly across replicates, indicating that strong selection for fitness recovery does exist. Our results indicate that recovery from inbreeding depression via standing genetic variation and mutation is likely to be constrained by the large number of segregating deleterious variants present in natural populations, limiting the capacity for recovery of small populations.
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Affiliation(s)
- Paula E Adams
- Department of Biological Sciences, University of Alabama, Tuscaloosa, AL, USA
| | - Anna B Crist
- Department of Genomes and Genetics, Institut Pasteur, Paris, France
| | - Ellen M Young
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR, USA
| | - John H Willis
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR, USA
| | - Patrick C Phillips
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR, USA
| | - Janna L Fierst
- Department of Biological Sciences, University of Alabama, Tuscaloosa, AL, USA
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Andersen EC, Rockman MV. Natural genetic variation as a tool for discovery in Caenorhabditis nematodes. Genetics 2022; 220:iyab156. [PMID: 35134197 PMCID: PMC8733454 DOI: 10.1093/genetics/iyab156] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2021] [Accepted: 09/11/2021] [Indexed: 11/12/2022] Open
Abstract
Over the last 20 years, studies of Caenorhabditis elegans natural diversity have demonstrated the power of quantitative genetic approaches to reveal the evolutionary, ecological, and genetic factors that shape traits. These studies complement the use of the laboratory-adapted strain N2 and enable additional discoveries not possible using only one genetic background. In this chapter, we describe how to perform quantitative genetic studies in Caenorhabditis, with an emphasis on C. elegans. These approaches use correlations between genotype and phenotype across populations of genetically diverse individuals to discover the genetic causes of phenotypic variation. We present methods that use linkage, near-isogenic lines, association, and bulk-segregant mapping, and we describe the advantages and disadvantages of each approach. The power of C. elegans quantitative genetic mapping is best shown in the ability to connect phenotypic differences to specific genes and variants. We will present methods to narrow genomic regions to candidate genes and then tests to identify the gene or variant involved in a quantitative trait. The same features that make C. elegans a preeminent experimental model animal contribute to its exceptional value as a tool to understand natural phenotypic variation.
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Affiliation(s)
- Erik C Andersen
- Department of Molecular Biosciences, Northwestern University, Evanston, IL 60201, USA
| | - Matthew V Rockman
- Department of Biology and Center for Genomics & Systems Biology, New York University, New York, NY 10003, USA
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10
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Lutz S, Van Dyke K, Feraru MA, Albert FW. Multiple epistatic DNA variants in a single gene affect gene expression in trans. Genetics 2022; 220:iyab208. [PMID: 34791209 PMCID: PMC8733636 DOI: 10.1093/genetics/iyab208] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2021] [Accepted: 11/09/2021] [Indexed: 01/08/2023] Open
Abstract
DNA variants that alter gene expression in trans are important sources of phenotypic variation. Nevertheless, the identity of trans-acting variants remains poorly understood. Single causal variants in several genes have been reported to affect the expression of numerous distant genes in trans. Whether these simple molecular architectures are representative of trans-acting variation is unknown. Here, we studied the large RAS signaling regulator gene IRA2, which contains variants with extensive trans-acting effects on gene expression in the yeast Saccharomyces cerevisiae. We used systematic CRISPR-based genome engineering and a sensitive phenotyping strategy to dissect causal variants to the nucleotide level. In contrast to the simple molecular architectures known so far, IRA2 contained at least seven causal nonsynonymous variants. The effects of these variants were modulated by nonadditive, epistatic interactions. Two variants at the 5'-end affected gene expression and growth only when combined with a third variant that also had no effect in isolation. Our findings indicate that the molecular basis of trans-acting genetic variation may be considerably more complex than previously appreciated.
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Affiliation(s)
- Sheila Lutz
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455, USA
| | - Krisna Van Dyke
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455, USA
| | - Matthew A Feraru
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455, USA
| | - Frank W Albert
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455, USA
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11
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Heaton A, Milligan E, Faulconer E, Allen A, Nguyen T, Weir SM, Glaberman S. Variation in copper sensitivity between laboratory and wild strains of Caenorhabditis elegans. CHEMOSPHERE 2022; 287:131883. [PMID: 34818820 DOI: 10.1016/j.chemosphere.2021.131883] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2021] [Revised: 08/09/2021] [Accepted: 08/11/2021] [Indexed: 06/13/2023]
Abstract
Ecological risk assessments of chemicals are frequently based on laboratory toxicity data from a small number of model species that may be reared in labs for years or decades. These populations can undergo many processes in the lab including artificial selection, founder effect, and genetic drift, and may not adequately represent their wild counterparts, potentially undermining the goal of protecting natural populations. Here we measure variation in lethality to copper chloride among strains of an emerging model species in toxicology, Caenorhabditis elegans. We tested four wild strains from Chile, Germany, Kenya, and Madeira (Portugal) against several versions of the standard laboratory N2 strain from Bristol, UK used in molecular biology. The four wild strains were more sensitive than any of the N2 strains tested with copper. We also found that the standard N2 strain cultured in the laboratory for >1 year was less sensitive than a recently cultured N2 strain as well as a cataloged ancestral version of the N2 strain. These results suggest that toxicologists should be cognizant of performing toxicity testing with long-held animal cultures, and should perhaps use multiple strains as well as renew cultures periodically in the laboratory. This study also shows that multi-strain toxicity testing with nematodes is highly achievable and useful for understanding variation in intra- and interspecific chemical sensitivity.
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Affiliation(s)
- Andrew Heaton
- Department of Biology, University of South Alabama, Mobile, AL, USA; Grand Bay National Estuarine Research Reserve, Moss Point, MS, USA
| | - Emma Milligan
- Department of Biology, University of South Alabama, Mobile, AL, USA
| | | | - Andrew Allen
- Department of Biology, University of South Alabama, Mobile, AL, USA
| | - Timothy Nguyen
- Department of Biology, University of South Alabama, Mobile, AL, USA
| | - Scott M Weir
- Department of Biology, Queens University of Charlotte, Charlotte, NC, USA
| | - Scott Glaberman
- Department of Biology, University of South Alabama, Mobile, AL, USA; Department of Environmental Science & Policy, George Mason University, Fairfax, VA, USA.
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Noble LM, Rockman MV, Teotónio H. Gene-level quantitative trait mapping in Caenorhabditis elegans. G3-GENES GENOMES GENETICS 2021; 11:6114457. [PMID: 33693602 PMCID: PMC8022935 DOI: 10.1093/g3journal/jkaa061] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/08/2020] [Accepted: 12/13/2020] [Indexed: 02/06/2023]
Abstract
The Caenorhabditis elegans multiparental experimental evolution (CeMEE) panel is a collection of genome-sequenced, cryopreserved recombinant inbred lines useful for mapping the evolution and genetic basis of quantitative traits. We have expanded the resource with new lines and new populations, and here report the genotype and haplotype composition of CeMEE version 2, including a large set of putative de novo mutations, and updated additive and epistatic mapping simulations. Additive quantitative trait loci explaining 4% of trait variance are detected with >80% power, and the median detection interval approaches single-gene resolution on the highly recombinant chromosome arms. Although CeMEE populations are derived from a long-term evolution experiment, genetic structure is dominated by variation present in the ancestral population.
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Affiliation(s)
- Luke M Noble
- Institut de Biologie, École Normale Supérieure, CNRS 8197, Inserm U1024, PSL Research University, F-75005 Paris, France.,Department of Biology, Center for Genomics and Systems Biology, New York University, New York, NY 10003, USA
| | - Matthew V Rockman
- Department of Biology, Center for Genomics and Systems Biology, New York University, New York, NY 10003, USA
| | - Henrique Teotónio
- Institut de Biologie, École Normale Supérieure, CNRS 8197, Inserm U1024, PSL Research University, F-75005 Paris, France
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13
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Evans KS, van Wijk MH, McGrath PT, Andersen EC, Sterken MG. From QTL to gene: C. elegans facilitates discoveries of the genetic mechanisms underlying natural variation. Trends Genet 2021; 37:933-947. [PMID: 34229867 DOI: 10.1016/j.tig.2021.06.005] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Revised: 06/01/2021] [Accepted: 06/03/2021] [Indexed: 11/15/2022]
Abstract
Although many studies have examined quantitative trait variation across many species, only a small number of genes and thereby molecular mechanisms have been discovered. Without these data, we can only speculate about evolutionary processes that underlie trait variation. Here, we review how quantitative and molecular genetics in the nematode Caenorhabditis elegans led to the discovery and validation of 37 quantitative trait genes over the past 15 years. Using these data, we can start to make inferences about evolution from these quantitative trait genes, including the roles that coding versus noncoding variation, gene family expansion, common versus rare variants, pleiotropy, and epistasis play in trait variation across this species.
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Affiliation(s)
- Kathryn S Evans
- Molecular Biosciences, Northwestern University, Evanston, IL 60208, USA; Interdisciplinary Biological Sciences Program, Northwestern University, Evanston, IL 60208, USA
| | - Marijke H van Wijk
- Laboratory of Nematology, Wageningen University and Research, 6708 PB, Wageningen, The Netherlands
| | - Patrick T McGrath
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA
| | - Erik C Andersen
- Molecular Biosciences, Northwestern University, Evanston, IL 60208, USA.
| | - Mark G Sterken
- Laboratory of Nematology, Wageningen University and Research, 6708 PB, Wageningen, The Netherlands.
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14
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Evans KS, Wit J, Stevens L, Hahnel SR, Rodriguez B, Park G, Zamanian M, Brady SC, Chao E, Introcaso K, Tanny RE, Andersen EC. Two novel loci underlie natural differences in Caenorhabditis elegans abamectin responses. PLoS Pathog 2021; 17:e1009297. [PMID: 33720993 PMCID: PMC7993787 DOI: 10.1371/journal.ppat.1009297] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Revised: 03/25/2021] [Accepted: 03/02/2021] [Indexed: 11/18/2022] Open
Abstract
Parasitic nematodes cause a massive worldwide burden on human health along with a loss of livestock and agriculture productivity. Anthelmintics have been widely successful in treating parasitic nematodes. However, resistance is increasing, and little is known about the molecular and genetic causes of resistance for most of these drugs. The free-living roundworm Caenorhabditis elegans provides a tractable model to identify genes that underlie resistance. Unlike parasitic nematodes, C. elegans is easy to maintain in the laboratory, has a complete and well annotated genome, and has many genetic tools. Using a combination of wild isolates and a panel of recombinant inbred lines constructed from crosses of two genetically and phenotypically divergent strains, we identified three genomic regions on chromosome V that underlie natural differences in response to the macrocyclic lactone (ML) abamectin. One locus was identified previously and encodes an alpha subunit of a glutamate-gated chloride channel (glc-1). Here, we validate and narrow two novel loci using near-isogenic lines. Additionally, we generate a list of prioritized candidate genes identified in C. elegans and in the parasite Haemonchus contortus by comparison of ML resistance loci. These genes could represent previously unidentified resistance genes shared across nematode species and should be evaluated in the future. Our work highlights the advantages of using C. elegans as a model to better understand ML resistance in parasitic nematodes.
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Affiliation(s)
- Kathryn S. Evans
- Molecular Biosciences, Northwestern University, Evanston, Illinois, United States of America
- Interdisciplinary Biological Sciences Program, Northwestern University, Evanston, Illinois, United States of America
| | - Janneke Wit
- Molecular Biosciences, Northwestern University, Evanston, Illinois, United States of America
| | - Lewis Stevens
- Molecular Biosciences, Northwestern University, Evanston, Illinois, United States of America
| | - Steffen R. Hahnel
- Molecular Biosciences, Northwestern University, Evanston, Illinois, United States of America
| | - Briana Rodriguez
- Molecular Biosciences, Northwestern University, Evanston, Illinois, United States of America
| | - Grace Park
- Molecular Biosciences, Northwestern University, Evanston, Illinois, United States of America
| | - Mostafa Zamanian
- Molecular Biosciences, Northwestern University, Evanston, Illinois, United States of America
| | - Shannon C. Brady
- Molecular Biosciences, Northwestern University, Evanston, Illinois, United States of America
- Interdisciplinary Biological Sciences Program, Northwestern University, Evanston, Illinois, United States of America
| | - Ellen Chao
- Molecular Biosciences, Northwestern University, Evanston, Illinois, United States of America
| | - Katherine Introcaso
- Molecular Biosciences, Northwestern University, Evanston, Illinois, United States of America
| | - Robyn E. Tanny
- Molecular Biosciences, Northwestern University, Evanston, Illinois, United States of America
| | - Erik C. Andersen
- Molecular Biosciences, Northwestern University, Evanston, Illinois, United States of America
- * E-mail:
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15
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Waller DM. Addressing Darwin's dilemma: Can pseudo-overdominance explain persistent inbreeding depression and load? Evolution 2021; 75:779-793. [PMID: 33598971 DOI: 10.1111/evo.14189] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2020] [Revised: 01/06/2021] [Accepted: 01/30/2021] [Indexed: 01/01/2023]
Abstract
Darwin spent years investigating the effects of self-fertilization, concluding that "nature abhors perpetual self-fertilization." Given that selection purges inbred populations of strongly deleterious mutations and drift fixes mild mutations, why does inbreeding depression (ID) persist in highly inbred taxa and why do no purely selfing taxa exist? Background selection, associations and interference among loci, and drift within small inbred populations all limit selection while often increasing fixation. These mechanisms help to explain why more inbred populations in most species consistently show more fixed load. This drift load is manifest in the considerable heterosis regularly observed in between-population crosses. Such heterosis results in subsequent high ID, suggesting a mechanism by which small populations could retain variation and inbreeding load. Multiple deleterious recessive mutations linked in repulsion generate pseudo-overdominance. Many tightly linked load loci could generate a balanced segregating load high enough to sustain ID over many generations. Such pseudo-overdominance blocks (or "PODs") are more likely to occur in regions of low recombination. They should also result in clear genetic signatures including genomic hotspots of heterozygosity; distinct haplotypes supporting alleles at intermediate frequency; and high linkage disequilibrium in and around POD regions. Simulation and empirical studies tend to support these predictions. Additional simulations and comparative genomic analyses should explore POD dynamics in greater detail to resolve whether PODs exist in sufficient strength and number to account for why ID and load persist within inbred lineages.
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Affiliation(s)
- Donald M Waller
- Department of Botany, University of Wisconsin-Madison, Madison, Wisconsin, 53706
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16
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Evans KS, Zdraljevic S, Stevens L, Collins K, Tanny RE, Andersen EC. Natural variation in the sequestosome-related gene, sqst-5, underlies zinc homeostasis in Caenorhabditis elegans. PLoS Genet 2020; 16:e1008986. [PMID: 33175833 PMCID: PMC7682890 DOI: 10.1371/journal.pgen.1008986] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Revised: 11/23/2020] [Accepted: 09/23/2020] [Indexed: 12/14/2022] Open
Abstract
Zinc is an essential trace element that acts as a co-factor for many enzymes and transcription factors required for cellular growth and development. Altering intracellular zinc levels can produce dramatic effects ranging from cell proliferation to cell death. To avoid such fates, cells have evolved mechanisms to handle both an excess and a deficiency of zinc. Zinc homeostasis is largely maintained via zinc transporters, permeable channels, and other zinc-binding proteins. Variation in these proteins might affect their ability to interact with zinc, leading to either increased sensitivity or resistance to natural zinc fluctuations in the environment. We can leverage the power of the roundworm nematode Caenorhabditis elegans as a tractable metazoan model for quantitative genetics to identify genes that could underlie variation in responses to zinc. We found that the laboratory-adapted strain (N2) is resistant and a natural isolate from Hawaii (CB4856) is sensitive to micromolar amounts of exogenous zinc supplementation. Using a panel of recombinant inbred lines, we identified two large-effect quantitative trait loci (QTL) on the left arm of chromosome III and the center of chromosome V that are associated with zinc responses. We validated and refined both QTL using near-isogenic lines (NILs) and identified a naturally occurring deletion in sqst-5, a sequestosome-related gene, that is associated with resistance to high exogenous zinc. We found that this deletion is relatively common across strains within the species and that variation in sqst-5 is associated with zinc resistance. Our results offer a possible mechanism for how organisms can respond to naturally high levels of zinc in the environment and how zinc homeostasis varies among individuals.
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Affiliation(s)
- Kathryn S. Evans
- Molecular Biosciences, Northwestern University, Evanston, Illinois, United States of America
- Interdisciplinary Biological Sciences Program, Northwestern University, Evanston, Illinois, United States of America
| | - Stefan Zdraljevic
- Molecular Biosciences, Northwestern University, Evanston, Illinois, United States of America
- Interdisciplinary Biological Sciences Program, Northwestern University, Evanston, Illinois, United States of America
| | - Lewis Stevens
- Molecular Biosciences, Northwestern University, Evanston, Illinois, United States of America
| | - Kimberly Collins
- Molecular Biosciences, Northwestern University, Evanston, Illinois, United States of America
| | - Robyn E. Tanny
- Molecular Biosciences, Northwestern University, Evanston, Illinois, United States of America
| | - Erik C. Andersen
- Molecular Biosciences, Northwestern University, Evanston, Illinois, United States of America
- Robert H. Lurie Comprehensive Cancer Center, Northwestern University, Chicago, Illinois, United States of America
- * E-mail:
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Sterken MG, Bevers RPJ, Volkers RJM, Riksen JAG, Kammenga JE, Snoek BL. Dissecting the eQTL Micro-Architecture in Caenorhabditis elegans. Front Genet 2020; 11:501376. [PMID: 33240309 PMCID: PMC7670075 DOI: 10.3389/fgene.2020.501376] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2019] [Accepted: 10/13/2020] [Indexed: 01/11/2023] Open
Abstract
The study of expression quantitative trait loci (eQTL) using natural variation in inbred populations has yielded detailed information about the transcriptional regulation of complex traits. Studies on eQTL using recombinant inbred lines (RILs) led to insights on cis and trans regulatory loci of transcript abundance. However, determining the underlying causal polymorphic genes or variants is difficult, but ultimately essential for the understanding of regulatory networks of complex traits. This requires insight into whether associated loci are single eQTL or a combination of closely linked eQTL, and how this QTL micro-architecture depends on the environment. We addressed these questions by testing for independent replication of previously mapped eQTL in Caenorhabditis elegans using new data from introgression lines (ILs). Both populations indicate that the overall heritability of gene expression, number, and position of eQTL differed among environments. Across environments we were able to replicate 70% of the cis- and 40% of the trans-eQTL using the ILs. Testing eight different simulation models, we suggest that additive effects explain up to 60-93% of RIL/IL heritability for all three environments. Closely linked eQTL explained up to 40% of RIL/IL heritability in the control environment whereas only 7% in the heat-stress and recovery environments. In conclusion, we show that reproducibility of eQTL was higher for cis vs. trans eQTL and that the environment affects the eQTL micro-architecture.
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Affiliation(s)
- Mark G. Sterken
- Laboratory of Nematology, Wageningen University & Research, Wageningen, Netherlands
| | - Roel P. J. Bevers
- Laboratory of Nematology, Wageningen University & Research, Wageningen, Netherlands
| | - Rita J. M. Volkers
- Laboratory of Nematology, Wageningen University & Research, Wageningen, Netherlands
| | - Joost A. G. Riksen
- Laboratory of Nematology, Wageningen University & Research, Wageningen, Netherlands
| | - Jan E. Kammenga
- Laboratory of Nematology, Wageningen University & Research, Wageningen, Netherlands
| | - Basten L. Snoek
- Laboratory of Nematology, Wageningen University & Research, Wageningen, Netherlands
- Theoretical Biology & Bioinformatics, Utrecht University, Utrecht, Netherlands
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Noble LM, Miah A, Kaur T, Rockman MV. The Ancestral Caenorhabditis elegans Cuticle Suppresses rol-1. G3 (BETHESDA, MD.) 2020; 10:2385-2395. [PMID: 32423919 PMCID: PMC7341120 DOI: 10.1534/g3.120.401336] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Accepted: 05/09/2020] [Indexed: 12/30/2022]
Abstract
Genetic background commonly modifies the effects of mutations. We discovered that worms mutant for the canonical rol-1 gene, identified by Brenner in 1974, do not roll in the genetic background of the wild strain CB4856. Using linkage mapping, association analysis and gene editing, we determined that N2 carries an insertion in the collagen gene col-182 that acts as a recessive enhancer of rol-1 rolling. From population and comparative genomics, we infer the insertion is derived in N2 and related laboratory lines, likely arising during the domestication of Caenorhabditis elegans, and breaking a conserved protein. The ancestral version of col-182 also modifies the phenotypes of four other classical cuticle mutant alleles, and the effects of natural genetic variation on worm shape and locomotion. These results underscore the importance of genetic background and the serendipity of Brenner's choice of strain.
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Affiliation(s)
- Luke M Noble
- Institut de Biologie, École Normale Supérieure, CNRS 8197, Inserm U1024, PSL Research University, F-75005 Paris, France
| | - Asif Miah
- Center for Genomics and Systems Biology, Department of Biology, New York University, NY, 10003
| | - Taniya Kaur
- Center for Genomics and Systems Biology, Department of Biology, New York University, NY, 10003
| | - Matthew V Rockman
- Center for Genomics and Systems Biology, Department of Biology, New York University, NY, 10003
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Flatt T. Life-History Evolution and the Genetics of Fitness Components in Drosophila melanogaster. Genetics 2020; 214:3-48. [PMID: 31907300 PMCID: PMC6944413 DOI: 10.1534/genetics.119.300160] [Citation(s) in RCA: 66] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2019] [Accepted: 10/03/2019] [Indexed: 12/28/2022] Open
Abstract
Life-history traits or "fitness components"-such as age and size at maturity, fecundity and fertility, age-specific rates of survival, and life span-are the major phenotypic determinants of Darwinian fitness. Analyzing the evolution and genetics of these phenotypic targets of selection is central to our understanding of adaptation. Due to its simple and rapid life cycle, cosmopolitan distribution, ease of maintenance in the laboratory, well-understood evolutionary genetics, and its versatile genetic toolbox, the "vinegar fly" Drosophila melanogaster is one of the most powerful, experimentally tractable model systems for studying "life-history evolution." Here, I review what has been learned about the evolution and genetics of life-history variation in D. melanogaster by drawing on numerous sources spanning population and quantitative genetics, genomics, experimental evolution, evolutionary ecology, and physiology. This body of work has contributed greatly to our knowledge of several fundamental problems in evolutionary biology, including the amount and maintenance of genetic variation, the evolution of body size, clines and climate adaptation, the evolution of senescence, phenotypic plasticity, the nature of life-history trade-offs, and so forth. While major progress has been made, important facets of these and other questions remain open, and the D. melanogaster system will undoubtedly continue to deliver key insights into central issues of life-history evolution and the genetics of adaptation.
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Affiliation(s)
- Thomas Flatt
- Department of Biology, University of Fribourg, CH-1700, Switzerland
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