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Dorken ME. Causes and consequences of sex ratio variation in plants. A commentary on: 'Life history characteristics and historical factors are important to explain regional variation in reproductive traits and genetic diversity in perennial mosses'. ANNALS OF BOTANY 2023; 132:viii-x. [PMID: 37793136 PMCID: PMC10550265 DOI: 10.1093/aob/mcad092] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/06/2023]
Abstract
This article comments on:
Irene Bisang, Johan Ehrlén, and Lars Hedenäs. Life-history characteristics and historical factors are important to explain regional variation in reproductive traits and genetic diversity in perennial mosses, Annals of Botany, Volume 132, Issue 1, 1 July 2023, Pages 29–42, https://doi.org/10.1093/aob/mcad045
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Affiliation(s)
- Marcel E Dorken
- Department of Biology, Trent University, 1600 West Bank Drive, K9L 0G2, Peterborough, Canada
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2
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Henshaw JM, Bittlingmaier M, Schärer L. Hermaphroditic origins of anisogamy. Philos Trans R Soc Lond B Biol Sci 2023; 378:20220283. [PMID: 36934747 PMCID: PMC10024982 DOI: 10.1098/rstb.2022.0283] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Accepted: 11/23/2022] [Indexed: 03/21/2023] Open
Abstract
Anisogamy-the size dimorphism of gametes-is the defining difference between the male and female sexual strategies. Game-theoretic thinking led to the first convincing explanation for the evolutionary origins of anisogamy in the 1970s. Since then, formal game-theoretic models have continued to refine our understanding of when and why anisogamy should evolve. Such models typically presume that the earliest anisogamous organisms had separate sexes. However, in most taxa, there is no empirical evidence to support this assumption. Here, we present a model of the coevolution of gamete size and sex allocation, which allows for anisogamy to emerge alongside either hermaphroditism or separate sexes. We show that hermaphroditic anisogamy can evolve directly from isogamous ancestors when the average size of spawning groups is small and fertilization is relatively efficient. Sex allocation under hermaphroditism becomes increasingly female-biased as group size decreases and the degree of anisogamy increases. When spawning groups are very small, our model also predicts the existence of complex isogamous organisms in which individuals allocate resources equally to two large gamete types. We discuss common, but potentially unwarranted, assumptions in the literature that could be relaxed in future models. This article is part of the theme issue 'Half a century of evolutionary games: a synthesis of theory, application and future directions'.
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Affiliation(s)
- Jonathan M. Henshaw
- Institute of Biology I, University of Freiburg, Hauptstraße 1, D-79104 Freiburg, Germany
| | - Markus Bittlingmaier
- Institute of Biology I, University of Freiburg, Hauptstraße 1, D-79104 Freiburg, Germany
- Theoretical and Experimental Ecology Station, CNRS, 2 route du CNRS, 09200 Moulis, France
| | - Lukas Schärer
- Zoological Institute, Department of Environmental Sciences, University of Basel, Basel CH-4051, Switzerland
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XY sex determination in a cnidarian. BMC Biol 2023; 21:32. [PMID: 36782149 PMCID: PMC9926710 DOI: 10.1186/s12915-023-01532-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2022] [Accepted: 01/31/2023] [Indexed: 02/15/2023] Open
Abstract
BACKGROUND Sex determination occurs across animal species, but most of our knowledge about its mechanisms comes from only a handful of bilaterian taxa. This limits our ability to infer the evolutionary history of sex determination within animals. RESULTS In this study, we generated a linkage map of the genome of the colonial cnidarian Hydractinia symbiolongicarpus and used it to demonstrate that this species has an XX/XY sex determination system. We demonstrate that the X and Y chromosomes have pseudoautosomal and non-recombining regions. We then use the linkage map and a method based on the depth of sequencing coverage to identify genes encoded in the non-recombining region and show that many of them have male gonad-specific expression. In addition, we demonstrate that recombination rates are enhanced in the female genome and that the haploid chromosome number in Hydractinia is n = 15. CONCLUSIONS These findings establish Hydractinia as a tractable non-bilaterian model system for the study of sex determination and the evolution of sex chromosomes.
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Trioecy is maintained as a time-stable mating system in the pink sea urchin Toxopneustes roseus from the Mexican Pacific. Sci Rep 2022; 12:21408. [PMID: 36496463 PMCID: PMC9741619 DOI: 10.1038/s41598-022-26059-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2022] [Accepted: 12/08/2022] [Indexed: 12/13/2022] Open
Abstract
Trioecy is a sexual system that consists of the co-occurrence of females, males and hermaphrodites in a population and is common in plants; however, in animals it is uncommon and poorly understood. In echinoderms, trioecy had never been recorded until now. Frequencies of females, males, and hermaphrodites were evaluated and gametogenic development was histologically characterized in a population of Toxopneustes roseus inhabiting the Mexican Pacific. Trioecy in this population is functional and temporally stable, since the three sexes coexisted in each sampling month. The hermaphrodites presented similar gametogenic development as the females and males and participated during the spawning season, contributing to the population's reproductive process. Trioecy is considered an evolutionarily transitory state, and it is extremely difficult to explain its presence in a species. We hypothesize that continuous ocean warming represents a threat to the survival of this population of T. roseus, since its early developmental stages, which represent a population bottleneck, are more vulnerable to high temperatures than other sea urchins inhabiting the area, while its population density is significantly lower. These conditions generate a strongly stressed environment, which is the determining factor that maintains the stability of trioecy in the species in which it has been studied.
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Renner SS, Müller NA. Sex determination and sex chromosome evolution in land plants. Philos Trans R Soc Lond B Biol Sci 2022; 377:20210210. [PMID: 35306895 PMCID: PMC8935313 DOI: 10.1098/rstb.2021.0210] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2022] [Accepted: 01/19/2022] [Indexed: 01/02/2023] Open
Abstract
Linnaeus's very first opus, written when he was 22 years old, dealt with the analogy that exists between plants and animals in how they 'propagate their species', and a revised version with a plate depicting the union of male and female Mercurialis annua plants became a foundational text on the sexuality of plants. The question how systems with separate males and females have evolved in sedentary organisms that appear ancestrally bisexual has fascinated biologists ever since. The phenomenon, termed dioecy, has important consequences for plant reproductive success and is of commercial interest since it affects seed quality and fruit production. This theme issue presents a series of articles that synthesize and challenge the current understanding of how plants achieve dioecy. The articles deal with a broad set of taxa, including Coccinia, Ginkgo, Mercurialis, Populus, Rumex and Silene, as well as overarching topics, such as the field's terminology, analogies with animal sex determination systems, evolutionary pathways to dioecy, dosage compensation, and the longevity of the two sexes. In this introduction, we focus on four topics, each addressed by several articles from different angles and with different conclusions. Our highlighting of unclear or controversial issues may help future studies to build on the current understanding and to ask new questions that will expand our knowledge of plant sexual systems. This article is part of the theme issue 'Sex determination and sex chromosome evolution in land plants'.
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Affiliation(s)
- Susanne S. Renner
- Department of Biology, Washington University, Saint Louis, MO 63130, USA
| | - Niels A. Müller
- Thünen-Institute of Forest Genetics, Sieker Landstrasse 2, 22927 Grosshansdorf, Germany
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Picard MAL, Vicoso B, Bertrand S, Escriva H. Diversity of Modes of Reproduction and Sex Determination Systems in Invertebrates, and the Putative Contribution of Genetic Conflict. Genes (Basel) 2021; 12:1136. [PMID: 34440310 PMCID: PMC8391622 DOI: 10.3390/genes12081136] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2021] [Revised: 07/08/2021] [Accepted: 07/11/2021] [Indexed: 12/30/2022] Open
Abstract
About eight million animal species are estimated to live on Earth, and all except those belonging to one subphylum are invertebrates. Invertebrates are incredibly diverse in their morphologies, life histories, and in the range of the ecological niches that they occupy. A great variety of modes of reproduction and sex determination systems is also observed among them, and their mosaic-distribution across the phylogeny shows that transitions between them occur frequently and rapidly. Genetic conflict in its various forms is a long-standing theory to explain what drives those evolutionary transitions. Here, we review (1) the different modes of reproduction among invertebrate species, highlighting sexual reproduction as the probable ancestral state; (2) the paradoxical diversity of sex determination systems; (3) the different types of genetic conflicts that could drive the evolution of such different systems.
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Affiliation(s)
- Marion Anne Lise Picard
- Sorbonne Université, CNRS, Biologie Intégrative des Organismes Marins (BIOM), Observatoire Océanologique, 66650 Banyuls-sur-Mer, France; (S.B.); (H.E.)
| | - Beatriz Vicoso
- Institute of Science and Technology Austria, Am Campus 1, 3400 Klosterneuburg, Austria;
| | - Stéphanie Bertrand
- Sorbonne Université, CNRS, Biologie Intégrative des Organismes Marins (BIOM), Observatoire Océanologique, 66650 Banyuls-sur-Mer, France; (S.B.); (H.E.)
| | - Hector Escriva
- Sorbonne Université, CNRS, Biologie Intégrative des Organismes Marins (BIOM), Observatoire Océanologique, 66650 Banyuls-sur-Mer, France; (S.B.); (H.E.)
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Carey SB, Jenkins J, Lovell JT, Maumus F, Sreedasyam A, Payton AC, Shu S, Tiley GP, Fernandez-Pozo N, Healey A, Barry K, Chen C, Wang M, Lipzen A, Daum C, Saski CA, McBreen JC, Conrad RE, Kollar LM, Olsson S, Huttunen S, Landis JB, Burleigh JG, Wickett NJ, Johnson MG, Rensing SA, Grimwood J, Schmutz J, McDaniel SF. Gene-rich UV sex chromosomes harbor conserved regulators of sexual development. SCIENCE ADVANCES 2021; 7:7/27/eabh2488. [PMID: 34193417 PMCID: PMC8245031 DOI: 10.1126/sciadv.abh2488] [Citation(s) in RCA: 41] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2021] [Accepted: 05/14/2021] [Indexed: 05/19/2023]
Abstract
Nonrecombining sex chromosomes, like the mammalian Y, often lose genes and accumulate transposable elements, a process termed degeneration. The correlation between suppressed recombination and degeneration is clear in animal XY systems, but the absence of recombination is confounded with other asymmetries between the X and Y. In contrast, UV sex chromosomes, like those found in bryophytes, experience symmetrical population genetic conditions. Here, we generate nearly gapless female and male chromosome-scale reference genomes of the moss Ceratodon purpureus to test for degeneration in the bryophyte UV sex chromosomes. We show that the moss sex chromosomes evolved over 300 million years ago and expanded via two chromosomal fusions. Although the sex chromosomes exhibit weaker purifying selection than autosomes, we find that suppressed recombination alone is insufficient to drive degeneration. Instead, the U and V sex chromosomes harbor thousands of broadly expressed genes, including numerous key regulators of sexual development across land plants.
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Affiliation(s)
- Sarah B Carey
- Department of Biology, University of Florida, Gainesville, FL, USA
| | - Jerry Jenkins
- Genome Sequencing Center, HudsonAlpha Institute for Biotechnology, Huntsville, AL, USA
| | - John T Lovell
- Genome Sequencing Center, HudsonAlpha Institute for Biotechnology, Huntsville, AL, USA
| | - Florian Maumus
- Université Paris-Saclay, INRAE, URGI, 78026 Versailles, France
| | - Avinash Sreedasyam
- Genome Sequencing Center, HudsonAlpha Institute for Biotechnology, Huntsville, AL, USA
| | - Adam C Payton
- Department of Biology, University of Florida, Gainesville, FL, USA
- RAPiD Genomics, Gainesville, FL, USA
| | - Shengqiang Shu
- U.S. Department of Energy Joint Genome Institute, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | | | | | - Adam Healey
- Genome Sequencing Center, HudsonAlpha Institute for Biotechnology, Huntsville, AL, USA
| | - Kerrie Barry
- U.S. Department of Energy Joint Genome Institute, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Cindy Chen
- U.S. Department of Energy Joint Genome Institute, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Mei Wang
- U.S. Department of Energy Joint Genome Institute, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Anna Lipzen
- U.S. Department of Energy Joint Genome Institute, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Chris Daum
- U.S. Department of Energy Joint Genome Institute, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Christopher A Saski
- Department of Plant and Environmental Sciences, Clemson University, Clemson, SC, USA
| | - Jordan C McBreen
- Department of Biology, University of Florida, Gainesville, FL, USA
| | - Roth E Conrad
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, USA
| | - Leslie M Kollar
- Department of Biology, University of Florida, Gainesville, FL, USA
| | - Sanna Olsson
- Department of Forest Ecology and Genetics, INIA-CIFOR, Madrid, Spain
| | - Sanna Huttunen
- Department of Biology and Biodiversity Unit, University of Turku, Turku, Finland
| | - Jacob B Landis
- L.H. Bailey Hortorium and Section of Plant Biology, School of Integrative Plant Science, Cornell University, Ithaca, NY, USA
| | | | - Norman J Wickett
- Negaunee Institute for Plant Conservation Science and Action, Chicago Botanic Garden, Glencoe, IL, USA
| | - Matthew G Johnson
- Department of Biological Sciences, Texas Tech University, Lubbock, TX, USA
| | - Stefan A Rensing
- Plant Cell Biology, University of Marburg, Marburg, Germany
- Center for Synthetic Microbiology (SYNMIKRO), University of Marburg, Hans-Meerwein-Straße 6, 35032 Marburg, Germany
- BIOSS Centre for Biological Signalling Studies, University of Freiburg, Schänzlestraße 18, 79104 Freiburg im Breisgau, Germany
| | - Jane Grimwood
- Genome Sequencing Center, HudsonAlpha Institute for Biotechnology, Huntsville, AL, USA
- U.S. Department of Energy Joint Genome Institute, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Jeremy Schmutz
- Genome Sequencing Center, HudsonAlpha Institute for Biotechnology, Huntsville, AL, USA
- U.S. Department of Energy Joint Genome Institute, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
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Tao W, Conte MA, Wang D, Kocher TD. Network architecture and sex chromosome turnovers: Do epistatic interactions shape patterns of sex chromosome replacement? Bioessays 2020; 43:e2000161. [PMID: 33283342 DOI: 10.1002/bies.202000161] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2020] [Revised: 11/04/2020] [Accepted: 11/05/2020] [Indexed: 11/11/2022]
Abstract
Recent studies have revealed an astonishing diversity of sex chromosomes in many vertebrate lineages, prompting questions about the mechanisms of sex chromosome turnover. While there is considerable population genetic theory about the evolutionary forces promoting sex chromosome replacement, this theory has not yet been integrated with our understanding of the molecular and developmental genetics of sex determination. Here, we review recent data to examine four questions about how the structure of gene networks influences the evolution of sex determination. We argue that patterns of epistasis, arising from the structure of genetic networks, may play an important role in regulating the rates and patterns of sex chromosome replacement.
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Affiliation(s)
- Wenjing Tao
- Key Laboratory of Freshwater Fish Reproduction and Development (Ministry of Education), Key Laboratory of Aquatic Science of Chongqing, School of Life Sciences, Southwest University, Chongqing, China
| | - Matthew A Conte
- Department of Biology, University of Maryland, College Park, Maryland, USA
| | - Deshou Wang
- Key Laboratory of Freshwater Fish Reproduction and Development (Ministry of Education), Key Laboratory of Aquatic Science of Chongqing, School of Life Sciences, Southwest University, Chongqing, China
| | - Thomas D Kocher
- Department of Biology, University of Maryland, College Park, Maryland, USA
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9
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Tempestini A, Massamba-N'Siala G, Vermandele F, Beaudreau N, Mortz M, Dufresne F, Calosi P. Extensive gene rearrangements in the mitogenomes of congeneric annelid species and insights on the evolutionary history of the genus Ophryotrocha. BMC Genomics 2020; 21:815. [PMID: 33225885 PMCID: PMC7682095 DOI: 10.1186/s12864-020-07176-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2019] [Accepted: 10/22/2020] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Annelids are one the most speciose and ecologically diverse groups of metazoans. Although a significant effort has been recently invested in sequencing genomes of a wide array of metazoans, many orders and families within the phylum Annelida are still represented by a single specimen of a single species. The genus of interstitial annelids Ophryotrocha (Dorvilleidae, Errantia, Annelida) is among these neglected groups, despite its extensive use as model organism in numerous studies on the evolution of life history, physiological and ecological traits. To compensate for the paucity of genomic information in this genus, we here obtained novel complete mitochondrial genomes of six Ophryotrocha species using next generation sequencing. In addition, we investigated the evolution of the reproductive mode in the Ophryotrocha genus using a phylogeny based on two mitochondrial markers (COXI and 16S rDNA) and one nuclear fragment (Histone H3). RESULTS Surprisingly, gene order was not conserved among the six Ophryotrocha species investigated, and varied greatly as compared to those found in other annelid species within the class Errantia. The mitogenome phylogeny for the six Ophryotrocha species displayed a separation of gonochoric and hermaphroditic species. However, this separation was not observed in the phylogeny based on the COX1, 16S rDNA, and H3 genes. Parsimony and Bayesian ancestral trait reconstruction indicated that gonochorism was the most parsimonious ancestral reproductive mode in Ophryotrocha spp. CONCLUSIONS Our results highlight the remarkably high level of gene order variation among congeneric species, even in annelids. This encourages the need for additional mitogenome sequencing of annelid taxa in order to properly understand its mtDNA evolution, high biodiversity and phylogenetic relationships.
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Affiliation(s)
- Astrid Tempestini
- Département de Biologie, Chimie et Géographie, Université du Québec à Rimouski, 300 Allée des Ursulines, Rimouski, QC, G5L 3A1, Canada
| | - Gloria Massamba-N'Siala
- Département de Biologie, Chimie et Géographie, Université du Québec à Rimouski, 300 Allée des Ursulines, Rimouski, QC, G5L 3A1, Canada
| | - Fanny Vermandele
- Département de Biologie, Chimie et Géographie, Université du Québec à Rimouski, 300 Allée des Ursulines, Rimouski, QC, G5L 3A1, Canada
| | - Nicholas Beaudreau
- Département de Biologie, Chimie et Géographie, Université du Québec à Rimouski, 300 Allée des Ursulines, Rimouski, QC, G5L 3A1, Canada
| | - Mathieu Mortz
- Département de Biologie, Chimie et Géographie, Université du Québec à Rimouski, 300 Allée des Ursulines, Rimouski, QC, G5L 3A1, Canada
| | - France Dufresne
- Département de Biologie, Chimie et Géographie, Université du Québec à Rimouski, 300 Allée des Ursulines, Rimouski, QC, G5L 3A1, Canada
| | - Piero Calosi
- Département de Biologie, Chimie et Géographie, Université du Québec à Rimouski, 300 Allée des Ursulines, Rimouski, QC, G5L 3A1, Canada.
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Hörandl E, Hadacek F. Oxygen, life forms, and the evolution of sexes in multicellular eukaryotes. Heredity (Edinb) 2020; 125:1-14. [PMID: 32415185 PMCID: PMC7413252 DOI: 10.1038/s41437-020-0317-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2019] [Revised: 04/26/2020] [Accepted: 04/26/2020] [Indexed: 12/27/2022] Open
Abstract
The evolutionary advantage of different sexual systems in multicellular eukaryotes is still not well understood, because the differentiation into male and female individuals halves offspring production compared with asexuality. Here we propose that various physiological adaptations to oxidative stress could have forged sessility versus motility, and consequently the evolution of sexual systems in multicellular animals, plants, and fungi. Photosynthesis causes substantial amounts of oxidative stress in photoautotrophic plants and, likewise, oxidative chemistry of polymer breakdown, cellulose and lignin, for saprotrophic fungi. In both cases, its extent precludes motility, an additional source of oxidative stress. Sessile life form and the lack of neuronal systems, however, limit options for mate recognition and adult sexual selection, resulting in inefficient mate-searching systems. Hence, sessility requires that all individuals can produce offspring, which is achieved by hermaphroditism in plants and/or by multiple mating types in fungi. In animals, motility requires neuronal systems, and muscle activity, both of which are highly sensitive to oxidative damage. As a consequence, motility has evolved in animals as heterotrophic organisms that (1) are not photosynthetically active, and (2) are not primary decomposers. Adaptations to motility provide prerequisites for an active mating behavior and efficient mate-searching systems. These benefits compensate for the "cost of males", and may explain the early evolution of sex chromosomes in metazoans. We conclude that different sexual systems evolved under the indirect physiological constraints of lifestyles.
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Affiliation(s)
- Elvira Hörandl
- Department of Systematics, Biodiversity and Evolution of Plants, University of Goettingen, Göttingen, Germany.
| | - Franz Hadacek
- Department of Plant Biochemistry, University of Goettingen, Göttingen, Germany
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11
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Carey SB, Jenkins J, Lovell JT, Maumus F, Sreedasyam A, Payton AC, Shu S, Tiley GP, Fernandez-pozo N, Barry K, Chen C, Wang M, Lipzen A, Daum C, Saski CA, Mcbreen JC, Conrad RE, Kollar LM, Olsson S, Huttunen S, Landis JB, Burleigh JG, Wickett NJ, Johnson MG, Rensing SA, Grimwood J, Schmutz J, Mcdaniel SF. The Ceratodon purpureus genome uncovers structurally complex, gene rich sex chromosomes.. [PMID: 0 DOI: 10.1101/2020.07.03.163634] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
AbstractNon-recombining sex chromosomes, like the mammalian Y, often lose genes and accumulate transposable elements, a process termed degeneration1,2. The correlation between suppressed recombination and degeneration is clear in animal XY systems1,2, but the absence of recombination is confounded with other asymmetries between the X and Y. In contrast, UV sex chromosomes, like those found in bryophytes, experience symmetrical population genetic conditions3,4. Here we test for degeneration in the bryophyte UV sex chromosome system through genomic comparisons with new female and male chromosome-scale reference genomes of the moss Ceratodon purpureus. We show that the moss sex chromosomes evolved over 300 million years ago and expanded via two chromosomal fusions. Although the sex chromosomes show signs of weaker purifying selection than autosomes, we find suppressed recombination alone is insufficient to drive gene loss on sex-specific chromosomes. Instead, the U and V sex chromosomes harbor thousands of broadly-expressed genes, including numerous key regulators of sexual development across land plants.
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12
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Atkins JB, Reisz RR, Maddin HC. Braincase simplification and the origin of lissamphibians. PLoS One 2019; 14:e0213694. [PMID: 30901341 PMCID: PMC6430379 DOI: 10.1371/journal.pone.0213694] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2018] [Accepted: 02/26/2019] [Indexed: 12/26/2022] Open
Abstract
Dissorophoidea, a group of temnospondyl tetrapods that first appear in the Late Carboniferous, is made up of two clades ⎼ Olsoniformes and Amphibamiformes (Branchiosauridae and Amphibamidae) ⎼ the latter of which is widely thought to have given rise to living amphibians (i.e., Lissamphibia). The lissamphibian braincase has a highly derived morphology with several secondarily lost elements; however, these losses have never been incorporated into phylogenetic analyses and thus the timing and nature of these evolutionary events remain unknown. Hindering research into this problem has been the lack of phylogenetic analyses of Dissorophoidea that includes both taxonomically dense sampling and specific characters to document changes in the braincase in the lineage leading to Lissamphibia. Here we build on a recent, broadly sampled dissorophoid phylogenetic analysis to visualize key events in the evolution of the lissamphibian braincase. Our ancestral character state reconstructions show a clear, step-wise trend towards reduction of braincase ossification leading to lissamphibians, including reduction of the sphenethmoid, loss of the basioccipital at the Amphibamiformes node, and further loss of both the basisphenoid and the hypoglossal nerve foramina at the Lissamphibia node. Our analysis confirms that the highly derived condition of the lissamphibian braincase is characterized by overall simplification in terms of the number and extent of chondrocranial ossifications.
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Affiliation(s)
- Jade B. Atkins
- Department of Earth Sciences, Carleton University, Ottawa, ON, Canada
- * E-mail:
| | - Robert R. Reisz
- Department of Biology, University of Toronto at Mississauga, Mississauga, ON, Canada
- International Center of Future Science, Dinosaur Evolution Research Center, Jilin University, Changchun, China
| | - Hillary C. Maddin
- Department of Earth Sciences, Carleton University, Ottawa, ON, Canada
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Santi M, Picchi L, Lorenzi MC. Dynamic modulation of reproductive strategies in a simultaneous hermaphrodite and preference for the male role. Anim Behav 2018. [DOI: 10.1016/j.anbehav.2018.10.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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