1
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Zhang H, Lundberg M, Ponnikas S, Hasselquist D, Hansson B. Male-biased recombination at chromosome ends in a songbird revealed by precisely mapping crossover positions. G3 (BETHESDA, MD.) 2024; 14:jkae150. [PMID: 38985659 PMCID: PMC11373659 DOI: 10.1093/g3journal/jkae150] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2024] [Revised: 06/17/2024] [Accepted: 06/24/2024] [Indexed: 07/12/2024]
Abstract
Recombination plays a crucial role in evolution by generating novel haplotypes and disrupting linkage between genes, thereby enhancing the efficiency of selection. Here, we analyze the genomes of 12 great reed warblers (Acrocephalus arundinaceus) in a 3-generation pedigree to identify precise crossover positions along the chromosomes. We located more than 200 crossovers and found that these were highly concentrated toward the telomeric ends of the chromosomes. Apart from this major pattern in the recombination landscape, we found significantly higher frequencies of crossovers in genic compared with intergenic regions, and in exons compared with introns. Moreover, while the number of recombination events was similar between the sexes, the crossovers were located significantly closer to the ends of paternal compared with maternal chromosomes. In conclusion, our study of the great reed warbler revealed substantial variation in crossover frequencies within chromosomes, with a distinct bias toward the sub-telomeric regions, particularly on the paternal side. These findings emphasize the importance of thoroughly screening the entire length of chromosomes to characterize the recombination landscape and uncover potential sex-biases in recombination.
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Affiliation(s)
- Hongkai Zhang
- Department of Biology, Lund University, 22362 Lund, Sweden
| | - Max Lundberg
- Department of Biology, Lund University, 22362 Lund, Sweden
| | - Suvi Ponnikas
- Department of Biology, University of Oulu, 90570 Oulu, Finland
| | | | - Bengt Hansson
- Department of Biology, Lund University, 22362 Lund, Sweden
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2
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Hay Mele B, Ruggiero MV, D'Alelio D. Population bottlenecks and sexual recombination shape diatom microevolution. Ecol Evol 2024; 14:e11464. [PMID: 39091335 PMCID: PMC11289787 DOI: 10.1002/ece3.11464] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2024] [Revised: 04/04/2024] [Accepted: 05/08/2024] [Indexed: 08/04/2024] Open
Abstract
Diatoms are single-celled organisms that contribute approximately 20% of the global primary production and play a crucial role in biogeochemical cycles and trophic chains. Despite their ecological importance, our knowledge of microevolution is limited. We developed a model using the SLiM evolutionary framework to address this knowledge gap. As a reference, we used the diatom Pseudo-nitzschia multistriata, which has been extensively studied in the Gulf of Naples. Our model recapitulates what we observe in natural populations, with microevolutionary processes that occur annually during a three-stage bloom phase. Interestingly, we found that non-bloom phases allow the population to maintain sex-generated diversity produced during blooms. This finding suggests that non-bloom phases are critical to counteract bloom-related pressures and mitigate genetic divergence at the species level. Moreover, our model showed that despite the consistent genetic differentiation during bloom phases, the population tends to return to pre-bloom states. While our model is limited to neutral dynamics, our study provides valuable insights into diatoms' microevolution, paving the way to explore the ecological implications of the life history dynamics of these organisms.
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Affiliation(s)
- Bruno Hay Mele
- Department of BiologyUniversity of Naples “Federico II”NaplesItaly
| | | | - Domenico D'Alelio
- Stazione Zoologica Anton DohrnNaplesItaly
- National Biodiversity Future Center (NBFC)PalermoItaly
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3
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Ruggiero MV, Buffoli M, Wolf KKE, D'Alelio D, Di Tuccio V, Lombardi E, Manfellotto F, Vitale L, Margiotta F, Sarno D, John U, Ferrante MI, Montresor M. Multiannual patterns of genetic structure and mating type ratios highlight the complex bloom dynamics of a marine planktonic diatom. Sci Rep 2024; 14:6028. [PMID: 38472358 DOI: 10.1038/s41598-024-56292-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Accepted: 03/05/2024] [Indexed: 03/14/2024] Open
Abstract
Understanding the genetic structure of populations and the processes responsible for its spatial and temporal dynamics is vital for assessing species' adaptability and survival in changing environments. We investigate the genetic fingerprinting of blooming populations of the marine diatom Pseudo-nitzschia multistriata in the Gulf of Naples (Mediterranean Sea) from 2008 to 2020. Strains were genotyped using microsatellite fingerprinting and natural samples were also analysed with Microsatellite Pool-seq Barcoding based on Illumina sequencing of microsatellite loci. Both approaches revealed a clonal expansion event in 2013 and a more stable genetic structure during 2017-2020 compared to previous years. The identification of a mating type (MT) determination gene allowed to assign MT to strains isolated over the years. MTs were generally at equilibrium with two notable exceptions, including the clonal bloom of 2013. The populations exhibited linkage equilibrium in most blooms, indicating that sexual reproduction leads to genetic homogenization. Our findings show that P. multistriata blooms exhibit a dynamic genetic and demographic composition over time, most probably determined by deeper-layer cell inocula. Occasional clonal expansions and MT imbalances can potentially affect the persistence and ecological success of planktonic diatoms.
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Affiliation(s)
| | - Marina Buffoli
- Department of Integrative Marine Ecology, Stazione Zoologica Anton Dohrn, Naples, Italy
| | - Klara K E Wolf
- Institut für Marine Ökosystem- und Fischereiwissenschaften, Universität Hamburg, Hamburg, Germany
- Limnological Institute, Environmental Genomics, University of Konstanz, Konstanz, Germany
| | - Domenico D'Alelio
- Department of Integrative Marine Ecology, Stazione Zoologica Anton Dohrn, Naples, Italy
| | - Viviana Di Tuccio
- Department of Integrative Marine Ecology, Stazione Zoologica Anton Dohrn, Naples, Italy
| | - Ernestina Lombardi
- Department of Integrative Marine Ecology, Stazione Zoologica Anton Dohrn, Naples, Italy
| | - Francesco Manfellotto
- Department of Integrative Marine Ecology, Stazione Zoologica Anton Dohrn, Naples, Italy
| | - Laura Vitale
- Department of Integrative Marine Ecology, Stazione Zoologica Anton Dohrn, Naples, Italy
| | - Francesca Margiotta
- Department of Research Infrastructures for Marine Biological Resources, Stazione Zoologica Anton Dohrn, Naples, Italy
| | - Diana Sarno
- Department of Research Infrastructures for Marine Biological Resources, Stazione Zoologica Anton Dohrn, Naples, Italy
| | - Uwe John
- Alfred-Wegener-Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
- Helmholtz Institute for Functional Marine Biodiversity, Oldenburg, Germany
| | - Maria Immacolata Ferrante
- Department of Integrative Marine Ecology, Stazione Zoologica Anton Dohrn, Naples, Italy
- Oceanography Section, National Institute of Oceanography and Applied Geophysics, Trieste, Italy
| | - Marina Montresor
- Department of Integrative Marine Ecology, Stazione Zoologica Anton Dohrn, Naples, Italy.
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4
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Sandler G, Agrawal AF, Wright SI. Population Genomics of the Facultatively Sexual Liverwort Marchantia polymorpha. Genome Biol Evol 2023; 15:evad196. [PMID: 37883717 PMCID: PMC10667032 DOI: 10.1093/gbe/evad196] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2022] [Revised: 10/15/2023] [Accepted: 10/18/2023] [Indexed: 10/28/2023] Open
Abstract
The population genomics of facultatively sexual organisms are understudied compared with their abundance across the tree of life. We explore patterns of genetic diversity in two subspecies of the facultatively sexual liverwort Marchantia polymorpha using samples from across Southern Ontario, Canada. Despite the ease with which M. polymorpha should be able to propagate asexually, we find no evidence of strictly clonal descent among our samples and little to no signal of isolation by distance. Patterns of identity-by-descent tract sharing further showed evidence of recent recombination and close relatedness between geographically distant isolates, suggesting long distance gene flow and at least a modest frequency of sexual reproduction. However, the M. polymorpha genome contains overall very low levels of nucleotide diversity and signs of inefficient selection evidenced by a relatively high fraction of segregating deleterious variants. We interpret these patterns as possible evidence of the action of linked selection and a small effective population size due to past generations of asexual propagation. Overall, the M. polymorpha genome harbors signals of a complex history of both sexual and asexual reproduction.
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Affiliation(s)
- George Sandler
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
| | - Aneil F Agrawal
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
- Center for Analysis of Genome Evolution and Function, University of Toronto, Toronto, Ontario, Canada
| | - Stephen I Wright
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
- Center for Analysis of Genome Evolution and Function, University of Toronto, Toronto, Ontario, Canada
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5
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Hasan AR, Lachapelle J, El-Shawa SA, Potjewyd R, Ford SA, Ness RW. Salt stress alters the spectrum of de novo mutation available to selection during experimental adaptation of Chlamydomonas reinhardtii. Evolution 2022; 76:2450-2463. [PMID: 36036481 DOI: 10.1111/evo.14604] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2022] [Accepted: 08/12/2022] [Indexed: 01/22/2023]
Abstract
The genetic basis of adaptation is driven by both selection and the spectrum of available mutations. Given that the rate of mutation is not uniformly distributed across the genome and varies depending on the environment, understanding the signatures of selection across the genome is aided by first establishing what the expectations of genetic change are from mutation. To determine the interaction between salt stress, selection, and mutation across the genome, we compared mutations observed in a selection experiment for salt tolerance in Chlamydomonas reinhardtii to those observed in mutation accumulation (MA) experiments with and without salt exposure. MA lines evolved under salt stress had a single-nucleotide mutation rate of 1.1 × 10 - 9 $1.1 \times 10^{-9}$ , similar to that of MA lines under standard conditions ( 9.6 × 10 - 10 $9.6 \times 10^{-10}$ ). However, we found that salt stress led to an increased rate of indel mutations, but that many of these mutations were removed under selection. Finally, lines adapted to salt also showed excess clustering of mutations in the genome and the co-expression network, suggesting a role for positive selection in retaining mutations in particular compartments of the genome during the evolution of salt tolerance. Our study shows that characterizing mutation rates and spectra expected under stress helps disentangle the effects of environment and selection during adaptation.
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Affiliation(s)
- Ahmed R Hasan
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, M5S 3G5, Canada.,Department of Biology, University of Toronto Mississauga, Mississauga, ON, L5L 1C6, Canada
| | - Josianne Lachapelle
- Department of Biology, University of Toronto Mississauga, Mississauga, ON, L5L 1C6, Canada
| | - Sara A El-Shawa
- Department of Biology, University of Toronto Mississauga, Mississauga, ON, L5L 1C6, Canada.,Department of Mathematical and Computational Sciences, University of Toronto Mississauga, Mississauga, ON, L5L 1C6, Canada
| | - Roman Potjewyd
- Department of Biology, University of Toronto Mississauga, Mississauga, ON, L5L 1C6, Canada
| | - Scott A Ford
- Department of Biology, University of Toronto Mississauga, Mississauga, ON, L5L 1C6, Canada
| | - Rob W Ness
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, M5S 3G5, Canada.,Department of Biology, University of Toronto Mississauga, Mississauga, ON, L5L 1C6, Canada.,Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada
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6
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Winbush A, Singh ND. Variation in fine-scale recombination rate in temperature-evolved Drosophila melanogaster populations in response to selection. G3 GENES|GENOMES|GENETICS 2022; 12:6663992. [PMID: 35961026 PMCID: PMC9526048 DOI: 10.1093/g3journal/jkac208] [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: 06/09/2022] [Accepted: 08/05/2022] [Indexed: 11/16/2022]
Abstract
Meiotic recombination plays a critical evolutionary role in maintaining fitness in response to selective pressures due to changing environments. Variation in recombination rate has been observed amongst and between species and populations and within genomes across numerous taxa. Studies have demonstrated a link between changes in recombination rate and selection, but the extent to which fine-scale recombination rate varies between evolved populations during the evolutionary period in response to selection is under active research. Here, we utilize a set of 3 temperature-evolved Drosophila melanogaster populations that were shown to have diverged in several phenotypes, including recombination rate, based on the temperature regime in which they evolved. Using whole-genome sequencing data from these populations, we generated linkage disequilibrium-based fine-scale recombination maps for each population. With these maps, we compare recombination rates and patterns among the 3 populations and show that they have diverged at fine scales but are conserved at broader scales. We further demonstrate a correlation between recombination rates and genomic variation in the 3 populations. Lastly, we show variation in localized regions of enhanced recombination rates, termed warm spots, between the populations with these warm spots and associated genes overlapping areas previously shown to have diverged in the 3 populations due to selection. These data support the existence of recombination modifiers in these populations which are subject to selection during evolutionary change.
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Affiliation(s)
- Ari Winbush
- Department of Biology, Institute of Ecology and Evolution, University of Oregon , Eugene, OR 97403, USA
| | - Nadia D Singh
- Department of Biology, Institute of Ecology and Evolution, University of Oregon , Eugene, OR 97403, USA
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7
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Guo F, Carbone I, Rasmussen DA. Recombination-aware phylogeographic inference using the structured coalescent with ancestral recombination. PLoS Comput Biol 2022; 18:e1010422. [PMID: 35984849 PMCID: PMC9447913 DOI: 10.1371/journal.pcbi.1010422] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2022] [Revised: 09/06/2022] [Accepted: 07/21/2022] [Indexed: 11/19/2022] Open
Abstract
Movement of individuals between populations or demes is often restricted, especially between geographically isolated populations. The structured coalescent provides an elegant theoretical framework for describing how movement between populations shapes the genealogical history of sampled individuals and thereby structures genetic variation within and between populations. However, in the presence of recombination an individual may inherit different regions of their genome from different parents, resulting in a mosaic of genealogical histories across the genome, which can be represented by an Ancestral Recombination Graph (ARG). In this case, different genomic regions may have different ancestral histories and so different histories of movement between populations. Recombination therefore poses an additional challenge to phylogeographic methods that aim to reconstruct the movement of individuals from genealogies, although also a potential benefit in that different loci may contain additional information about movement. Here, we introduce the Structured Coalescent with Ancestral Recombination (SCAR) model, which builds on recent approximations to the structured coalescent by incorporating recombination into the ancestry of sampled individuals. The SCAR model allows us to infer how the migration history of sampled individuals varies across the genome from ARGs, and improves estimation of key population genetic parameters such as population sizes, recombination rates and migration rates. Using the SCAR model, we explore the potential and limitations of phylogeographic inference using full ARGs. We then apply the SCAR to lineages of the recombining fungus Aspergillus flavus sampled across the United States to explore patterns of recombination and migration across the genome.
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Affiliation(s)
- Fangfang Guo
- Department of Entomology and Plant Pathology, North Carolina State University, Raleigh, North Carolina, United States of America
| | - Ignazio Carbone
- Department of Entomology and Plant Pathology, North Carolina State University, Raleigh, North Carolina, United States of America
- Center for Integrated Fungal Research, North Carolina State University, Raleigh, North Carolina, United States of America
| | - David A. Rasmussen
- Department of Entomology and Plant Pathology, North Carolina State University, Raleigh, North Carolina, United States of America
- Bioinformatics Research Center, North Carolina State University, Raleigh, North Carolina, United States of America
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8
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Abstract
We discuss the genetic, demographic, and selective forces that are likely to be at play in restricting observed levels of DNA sequence variation in natural populations to a much smaller range of values than would be expected from the distribution of census population sizes alone-Lewontin's Paradox. While several processes that have previously been strongly emphasized must be involved, including the effects of direct selection and genetic hitchhiking, it seems unlikely that they are sufficient to explain this observation without contributions from other factors. We highlight a potentially important role for the less-appreciated contribution of population size change; specifically, the likelihood that many species and populations may be quite far from reaching the relatively high equilibrium diversity values that would be expected given their current census sizes.
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Affiliation(s)
- Brian Charlesworth
- Institute of Ecology and Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Jeffrey D Jensen
- School of Life Sciences, Arizona State University, Tempe, AZ, USA
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9
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Böndel KB, Samuels T, Craig RJ, Ness RW, Colegrave N, Keightley PD. The distribution of fitness effects of spontaneous mutations in Chlamydomonas reinhardtii inferred using frequency changes under experimental evolution. PLoS Genet 2022; 18:e1009840. [PMID: 35704655 PMCID: PMC9239454 DOI: 10.1371/journal.pgen.1009840] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Revised: 06/28/2022] [Accepted: 04/13/2022] [Indexed: 12/23/2022] Open
Abstract
The distribution of fitness effects (DFE) for new mutations is fundamental for many aspects of population and quantitative genetics. In this study, we have inferred the DFE in the single-celled alga Chlamydomonas reinhardtii by estimating changes in the frequencies of 254 spontaneous mutations under experimental evolution and equating the frequency changes of linked mutations with their selection coefficients. We generated seven populations of recombinant haplotypes by crossing seven independently derived mutation accumulation lines carrying an average of 36 mutations in the haploid state to a mutation-free strain of the same genotype. We then allowed the populations to evolve under natural selection in the laboratory by serial transfer in liquid culture. We observed substantial and repeatable changes in the frequencies of many groups of linked mutations, and, surprisingly, as many mutations were observed to increase as decrease in frequency. Mutation frequencies were highly repeatable among replicates, suggesting that selection was the cause of the observed allele frequency changes. We developed a Bayesian Monte Carlo Markov Chain method to infer the DFE. This computes the likelihood of the observed distribution of changes of frequency, and obtains the posterior distribution of the selective effects of individual mutations, while assuming a two-sided gamma distribution of effects. We infer that the DFE is a highly leptokurtic distribution, and that approximately equal proportions of mutations have positive and negative effects on fitness. This result is consistent with what we have observed in previous work on a different C. reinhardtii strain, and suggests that a high fraction of new spontaneously arisen mutations are advantageous in a simple laboratory environment.
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Affiliation(s)
- Katharina B. Böndel
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Toby Samuels
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Rory J. Craig
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Rob W. Ness
- Department of Biology, William G. Davis Building, University of Toronto, Mississauga, Canada
| | - Nick Colegrave
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Peter D. Keightley
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
- * E-mail:
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10
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Benites LF, Bucchini F, Sanchez-Brosseau S, Grimsley N, Vandepoele K, Piganeau G. Evolutionary Genomics of Sex-Related Chromosomes at the Base of the Green Lineage. Genome Biol Evol 2021; 13:6380139. [PMID: 34599324 PMCID: PMC8557840 DOI: 10.1093/gbe/evab216] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/11/2021] [Indexed: 12/11/2022] Open
Abstract
Although sex is now accepted as a ubiquitous and ancestral feature of eukaryotes, direct observation of sex is still lacking in most unicellular eukaryotic lineages. Evidence of sex is frequently indirect and inferred from the identification of genes involved in meiosis from whole genome data and/or the detection of recombination signatures from genetic diversity in natural populations. In haploid unicellular eukaryotes, sex-related chromosomes are named mating-type (MTs) chromosomes and generally carry large genomic regions where recombination is suppressed. These regions have been characterized in Fungi and Chlorophyta and determine gamete compatibility and fusion. Two candidate MT+ and MT− alleles, spanning 450–650 kb, have recently been described in Ostreococcus tauri, a marine phytoplanktonic alga from the Mamiellophyceae class, an early diverging branch in the green lineage. Here, we investigate the architecture and evolution of these candidate MT+ and MT− alleles. We analyzed the phylogenetic profile and GC content of MT gene families in eight different genomes whose divergence has been previously estimated at up to 640 Myr, and found evidence that the divergence of the two MT alleles predates speciation in the Ostreococcus genus. Phylogenetic profiles of MT trans-specific polymorphisms in gametologs disclosed candidate MTs in two additional species, and possibly a third. These Mamiellales MT candidates are likely to be the oldest mating-type loci described to date, which makes them fascinating models to investigate the evolutionary mechanisms of haploid sex determination in eukaryotes.
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Affiliation(s)
- Luis Felipe Benites
- Integrative Biology of Marine Organisms (BIOM), Sorbonne University, CNRS, Oceanological Observatory of Banyuls, Banyuls-sur-Mer, France
| | - François Bucchini
- Department of Plant Biotechnology and Bioinformatics, Ghent University, Belgium.,VIB Center for Plant Systems Biology, Ghent, Belgium
| | - Sophie Sanchez-Brosseau
- Integrative Biology of Marine Organisms (BIOM), Sorbonne University, CNRS, Oceanological Observatory of Banyuls, Banyuls-sur-Mer, France
| | - Nigel Grimsley
- Integrative Biology of Marine Organisms (BIOM), Sorbonne University, CNRS, Oceanological Observatory of Banyuls, Banyuls-sur-Mer, France
| | - Klaas Vandepoele
- Department of Plant Biotechnology and Bioinformatics, Ghent University, Belgium.,VIB Center for Plant Systems Biology, Ghent, Belgium.,Bioinformatics Institute Ghent, Ghent University, Belgium
| | - Gwenaël Piganeau
- Integrative Biology of Marine Organisms (BIOM), Sorbonne University, CNRS, Oceanological Observatory of Banyuls, Banyuls-sur-Mer, France
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11
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Craig RJ, Hasan AR, Ness RW, Keightley PD. Comparative genomics of Chlamydomonas. THE PLANT CELL 2021; 33:1016-1041. [PMID: 33793842 PMCID: PMC8226300 DOI: 10.1093/plcell/koab026] [Citation(s) in RCA: 35] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Accepted: 01/22/2021] [Indexed: 05/06/2023]
Abstract
Despite its role as a reference organism in the plant sciences, the green alga Chlamydomonas reinhardtii entirely lacks genomic resources from closely related species. We present highly contiguous and well-annotated genome assemblies for three unicellular C. reinhardtii relatives: Chlamydomonas incerta, Chlamydomonas schloesseri, and the more distantly related Edaphochlamys debaryana. The three Chlamydomonas genomes are highly syntenous with similar gene contents, although the 129.2 Mb C. incerta and 130.2 Mb C. schloesseri assemblies are more repeat-rich than the 111.1 Mb C. reinhardtii genome. We identify the major centromeric repeat in C. reinhardtii as a LINE transposable element homologous to Zepp (the centromeric repeat in Coccomyxa subellipsoidea) and infer that centromere locations and structure are likely conserved in C. incerta and C. schloesseri. We report extensive rearrangements, but limited gene turnover, between the minus mating type loci of these Chlamydomonas species. We produce an eight-species core-Reinhardtinia whole-genome alignment, which we use to identify several hundred false positive and missing genes in the C. reinhardtii annotation and >260,000 evolutionarily conserved elements in the C. reinhardtii genome. In summary, these resources will enable comparative genomics analyses for C. reinhardtii, significantly extending the analytical toolkit for this emerging model system.
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Affiliation(s)
| | - Ahmed R Hasan
- Department of Biology, University of Toronto Mississauga, Mississauga, Onatrio, Canada L5L 1C6
| | - Rob W Ness
- Department of Biology, University of Toronto Mississauga, Mississauga, Onatrio, Canada L5L 1C6
| | - Peter D Keightley
- School of Biological Sciences, Institute of Evolutionary Biology, University of Edinburgh, EH9 3FL Edinburgh, UK
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12
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Berríos-Caro E, Galla T, Constable GWA. Switching environments, synchronous sex, and the evolution of mating types. Theor Popul Biol 2021; 138:28-42. [PMID: 33639174 DOI: 10.1016/j.tpb.2021.02.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Revised: 02/11/2021] [Accepted: 02/12/2021] [Indexed: 01/31/2023]
Abstract
While facultative sex is common in sexually reproducing species, for reasons of tractability most mathematical models assume that such sex is asynchronous in the population. In this paper, we develop a model of switching environments to instead capture the effect of an entire population transitioning synchronously between sexual and asexual modes of reproduction. We use this model to investigate the evolution of the number of self-incompatible mating types in finite populations, which empirically can range from two to thousands. When environmental switching is fast, we recover the results of earlier studies that implicitly assumed populations were engaged in asynchronous sexual reproduction. However when the environment switches slowly, we see deviations from previous asynchronous theory, including a lower number of mating types at equilibrium and bimodality in the stationary distribution of mating types. We provide analytic approximations for both the fast and slow switching regimes, as well as a numerical scheme based on the Kolmogorov equations for the system to quickly evaluate the model dynamics at intermediate parameters. Our approach exploits properties of integer partitions in number theory. We also demonstrate how additional biological processes such as selective sweeps can be accounted for in this switching environment framework, showing that beneficial mutations can further erode mating type diversity in synchronous facultatively sexual populations.
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Affiliation(s)
- Ernesto Berríos-Caro
- Theoretical Physics, Department of Physics and Astronomy, School of Natural Sciences, Faculty of Science and Engineering, The University of Manchester, Manchester M13 9PL, United Kingdom.
| | - Tobias Galla
- Instituto de Física Interdisciplinar y Sistemas Complejos IFISC (CSIC-UIB), 07122 Palma de Mallorca, Spain; Theoretical Physics, Department of Physics and Astronomy, School of Natural Sciences, Faculty of Science and Engineering, The University of Manchester, Manchester M13 9PL, United Kingdom
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