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Charlesworth D, Qiu S, Bergero R, Gardner J, Keegan K, Yong L, Hastings A, Konczal M. Has recombination changed during the recent evolution of the guppy Y chromosome? Genetics 2024; 226:iyad198. [PMID: 37956094 DOI: 10.1093/genetics/iyad198] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2023] [Revised: 10/23/2023] [Accepted: 10/27/2023] [Indexed: 11/15/2023] Open
Abstract
Genome sequencing and genetic mapping of molecular markers have demonstrated nearly complete Y-linkage across much of the guppy (Poecilia reticulata) XY chromosome pair. Predominant Y-linkage of factors controlling visible male-specific coloration traits also suggested that these polymorphisms are sexually antagonistic (SA). However, occasional exchanges with the X are detected, and recombination patterns also appear to differ between natural guppy populations, suggesting ongoing evolution of recombination suppression under selection created by partially sex-linked SA polymorphisms. We used molecular markers to directly estimate genetic maps in sires from 4 guppy populations. The maps are very similar, suggesting that their crossover patterns have not recently changed. Our maps are consistent with population genomic results showing that variants within the terminal 5 Mb of the 26.5 Mb sex chromosome, chromosome 12, are most clearly associated with the maleness factor, albeit incompletely. We also confirmed occasional crossovers proximal to the male-determining region, defining a second, rarely recombining, pseudo-autosomal region, PAR2. This fish species may therefore have no completely male-specific region (MSY) more extensive than the male-determining factor. The positions of the few crossover events suggest a location for the male-determining factor within a physically small repetitive region. A sex-reversed XX male had few crossovers in PAR2, suggesting that this region's low crossover rate depends on the phenotypic, not the genetic, sex. Thus, rare individuals whose phenotypic and genetic sexes differ, and/or occasional PAR2 crossovers in males can explain the failure to detect fully Y-linked variants.
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Affiliation(s)
- Deborah Charlesworth
- School of Biological Sciences, Institute of Ecology and Evolution, University of Edinburgh, Charlotte Auerbach Road, Edinburgh EH9 3LF, UK
| | - Suo Qiu
- School of Biological Sciences, Institute of Ecology and Evolution, University of Edinburgh, Charlotte Auerbach Road, Edinburgh EH9 3LF, UK
| | - Roberta Bergero
- Scottish Rural Agricultural College, Peter Wilson Building, King's Buildings, W Mains Rd, Edinburgh EH9 3JG, UK
| | - Jim Gardner
- School of Biological Sciences, Institute of Ecology and Evolution, University of Edinburgh, Charlotte Auerbach Road, Edinburgh EH9 3LF, UK
| | - Karen Keegan
- School of Biological Sciences, Institute of Ecology and Evolution, University of Edinburgh, Charlotte Auerbach Road, Edinburgh EH9 3LF, UK
| | - Lengxob Yong
- Centre for Ecology and Conservation, College of Life and Environmental Sciences, University of Exeter, Penryn TR10 9FE, UK
- South Carolina Department of Natural Resources, Marine Resources Research Institute, P.O. Box 12559 Charleston, SC 29422-2559, USA
| | - Abigail Hastings
- School of Biological Sciences, Institute of Ecology and Evolution, University of Edinburgh, Charlotte Auerbach Road, Edinburgh EH9 3LF, UK
| | - Mateusz Konczal
- Evolutionary Biology Group, Faculty of Biology, Adam Mickiewicz University, 60-614 Poznań, Poland
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Qiu S, Yong L, Wilson A, Croft DP, Graham C, Charlesworth D. Partial sex linkage and linkage disequilibrium on the guppy sex chromosome. Mol Ecol 2022; 31:5524-5537. [PMID: 36005298 PMCID: PMC9826361 DOI: 10.1111/mec.16674] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2022] [Revised: 08/01/2022] [Accepted: 08/09/2022] [Indexed: 01/11/2023]
Abstract
The guppy Y chromosome has been considered a model system for the evolution of suppressed recombination between sex chromosomes, and it has been proposed that complete sex-linkage has evolved across about 3 Mb surrounding this fish's sex-determining locus, followed by recombination suppression across a further 7 Mb of the 23 Mb XY pair, forming younger "evolutionary strata". Sequences of the guppy genome show that Y is very similar to the X chromosome. Knowing which parts of the Y are completely nonrecombining, and whether there is indeed a large completely nonrecombining region, are important for understanding its evolution. Here, we describe analyses of PoolSeq data in samples from within multiple natural populations from Trinidad, yielding new results that support previous evidence for occasional recombination between the guppy Y and X. We detected recent demographic changes, notably that downstream populations have higher synonymous site diversity than upstream ones and other expected signals of bottlenecks. We detected evidence of associations between sequence variants and the sex-determining locus, rather than divergence under a complete lack of recombination. Although recombination is infrequent, it is frequent enough that associations with SNPs can suggest the region in which the sex-determining locus must be located. Diversity is elevated across a physically large region of the sex chromosome, conforming to predictions for a genome region with infrequent recombination that carries one or more sexually antagonistic polymorphisms. However, no consistently male-specific variants were found, supporting the suggestion that any completely sex-linked region may be very small.
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Affiliation(s)
- Suo Qiu
- Institute of Evolutionary Biology, School of Biological SciencesUniversity of EdinburghEdinburghUK
| | - Lengxob Yong
- Centre for Ecology and Conservation, College of Life and Environmental SciencesUniversity of ExeterPenrynUK,Marine Resources Research InstituteSouth Carolina Department of Natural ResourcesCharlestonSouth CarolinaUSA
| | - Alastair Wilson
- Centre for Ecology and Conservation, College of Life and Environmental SciencesUniversity of ExeterPenrynUK
| | - Darren P. Croft
- Centre for Research in Animal Behaviour, College of Life and Environmental SciencesUniversity of ExeterExeterUK
| | - Chay Graham
- Institute of Evolutionary Biology, School of Biological SciencesUniversity of EdinburghEdinburghUK
| | - Deborah Charlesworth
- Institute of Evolutionary Biology, School of Biological SciencesUniversity of EdinburghEdinburghUK
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Charlesworth D, Bergero R, Graham C, Gardner J, Yong L. Locating the Sex Determining Region of Linkage Group 12 of Guppy ( Poecilia reticulata). G3 (Bethesda) 2020; 10:3639-3649. [PMID: 32753367 PMCID: PMC7534449 DOI: 10.1534/g3.120.401573] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Accepted: 07/29/2020] [Indexed: 01/04/2023]
Abstract
Despite over 100 years of study, the location of the fully sex-linked region of the guppy (Poecilia reticulata) carrying the male-determining locus, and the regions where the XY pair recombine, remain unclear. Previous population genomics studies to determine these regions used small samples from recently bottlenecked captive populations, which increase the false positive rate of associations between individuals' sexes and SNPs. Using new data from multiple natural populations, we show that a recently proposed candidate for this species' male-determining gene is probably not completely sex-linked, leaving the maleness factor still unidentified. Variants in the chromosome 12 region carrying the candidate gene sometimes show linkage disequilibrium with the sex-determining factor, but no consistently male-specific variant has yet been found. Our genetic mapping with molecular markers spread across chromosome 12 confirms that this is the guppy XY pair. We describe two families with recombinants between the X and Y chromosomes, which confirm that the male-determining locus is in the region identified by all previous studies, near the terminal pseudo-autosomal region (PAR), which crosses over at a very high rate in males. We correct the PAR marker order, and assign two unplaced scaffolds to the PAR. We also detect a duplication, with one copy in the male-determining region, explaining signals of sex linkage in a more proximal region.
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Affiliation(s)
- Deborah Charlesworth
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, West Mains Road, EH9 3LF, UK
| | - Roberta Bergero
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, West Mains Road, EH9 3LF, UK
| | - Chay Graham
- University of Cambridge, Department of Biochemistry, Sanger Building, 80 Tennis Ct Rd, Cambridge CB2 1GA, UK
| | - Jim Gardner
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, West Mains Road, EH9 3LF, UK
| | - Lengxob Yong
- Centre for Ecology and Conservation, University of Exeter, Penryn, Falmouth, Cornwall, TR10 9FE, UK
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Abstract
Although individuals in most flowering plant species, and in many haploid plants, have both sex functions, dioecious species-in which individuals have either male or female functions only-are scattered across many taxonomic groups, and many species have genetic sex determination. Among these, some have visibly heteromorphic sex chromosomes, and molecular genetic studies are starting to uncover sex-linked markers in others, showing that they too have fully sex-linked regions that are either too small or are located in chromosomes that are too small to be cytologically detectable from lack of pairing, lack of visible crossovers, or accumulation of heterochromatin. Detailed study is revealing that, like animal sex chromosomes, plant sex-linked regions show evidence for accumulation of repetitive sequences and genetic degeneration. Estimating when recombination stopped confirms the view that many plants have young sex-linked regions, making plants of great interest for studying the timescale of these changes.
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Affiliation(s)
- Deborah Charlesworth
- Institute of Evolutionary Biology, University of Edinburgh, Edinburgh EH9 3FL, United Kingdom;
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Abstract
A minority of angiosperms have male and female flowers separated in distinct individuals (dioecy), and most dioecious plants do not have cytologically different (heteromorphic) sex chromosomes. Plants nevertheless have several advantages for the study of sex chromosome evolution, as genetic sex determination has evolved repeatedly and is often absent in close relatives. I review sex-determining regions in non-model plant species, which may help us to understand when and how (and, potentially, test hypotheses about why) recombination suppression evolves within young sex chromosomes. I emphasize high-throughput sequencing approaches that are increasingly being applied to plants to test for non-recombining regions. These data are particularly illuminating when combined with sequence data that allow phylogenetic analyses, and estimates of when these regions evolved. Together with comparative genetic mapping, this has revealed that sex-determining loci and sex-linked regions evolved independently in many plant lineages, sometimes in closely related dioecious species, and often within the past few million years. In reviewing recent progress, I suggest areas for future work, such as the use of phylogenies to allow the informed choice of outgroup species suitable for inferring the directions of changes, including testing whether Y chromosome-like regions are undergoing genetic degeneration, a predicted consequence of losing recombination.
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Affiliation(s)
- Deborah Charlesworth
- Institute of Evolutionary Biology, University of Edinburgh, Ashworth Lab, King's Buildings, W. Mains Road, Edinburgh, EH9 3FL, UK
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