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Lasne C, Elkrewi M, Toups MA, Layana L, Macon A, Vicoso B. The Scorpionfly (Panorpa cognata) Genome Highlights Conserved and Derived Features of the Peculiar Dipteran X Chromosome. Mol Biol Evol 2023; 40:msad245. [PMID: 37988296 PMCID: PMC10715201 DOI: 10.1093/molbev/msad245] [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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2023] [Revised: 10/05/2023] [Accepted: 11/07/2023] [Indexed: 11/23/2023] Open
Abstract
Many insects carry an ancient X chromosome-the Drosophila Muller element F-that likely predates their origin. Interestingly, the X has undergone turnover in multiple fly species (Diptera) after being conserved for more than 450 My. The long evolutionary distance between Diptera and other sequenced insect clades makes it difficult to infer what could have contributed to this sudden increase in rate of turnover. Here, we produce the first genome and transcriptome of a long overlooked sister-order to Diptera: Mecoptera. We compare the scorpionfly Panorpa cognata X-chromosome gene content, expression, and structure to that of several dipteran species as well as more distantly related insect orders (Orthoptera and Blattodea). We find high conservation of gene content between the mecopteran X and the dipteran Muller F element, as well as several shared biological features, such as the presence of dosage compensation and a low amount of genetic diversity, consistent with a low recombination rate. However, the 2 homologous X chromosomes differ strikingly in their size and number of genes they carry. Our results therefore support a common ancestry of the mecopteran and ancestral dipteran X chromosomes, and suggest that Muller element F shrank in size and gene content after the split of Diptera and Mecoptera, which may have contributed to its turnover in dipteran insects.
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Affiliation(s)
- Clementine Lasne
- Institute of Science and Technology Austria, Klosterneuburg, Austria
| | - Marwan Elkrewi
- Institute of Science and Technology Austria, Klosterneuburg, Austria
| | - Melissa A Toups
- Department of Life and Environmental Sciences, Bournemouth University, Poole, UK
| | - Lorena Layana
- Institute of Science and Technology Austria, Klosterneuburg, Austria
| | - Ariana Macon
- Institute of Science and Technology Austria, Klosterneuburg, Austria
| | - Beatriz Vicoso
- Institute of Science and Technology Austria, Klosterneuburg, Austria
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2
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Toups MA, Vicoso B. The X chromosome of insects likely predates the origin of class Insecta. Evolution 2023; 77:2504-2511. [PMID: 37738212 DOI: 10.1093/evolut/qpad169] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2023] [Revised: 09/04/2023] [Accepted: 09/18/2023] [Indexed: 09/24/2023]
Abstract
Sex chromosomes have evolved independently multiple times, but why some are conserved for more than 100 million years whereas others turnover rapidly remains an open question. Here, we examine the homology of sex chromosomes across nine orders of insects, plus the outgroup springtails. We find that the X chromosome is likely homologous across insects and springtails; the only exception is in the Lepidoptera, which has lost the X and now has a ZZ/ZW sex-chromosome system. These results suggest the ancestral insect X chromosome has persisted for more than 450 million years-the oldest known sex chromosome to date. Further, we propose that the shrinking of gene content the dipteran X chromosome has allowed for a burst of sex-chromosome turnover that is absent from other speciose insect orders.
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Affiliation(s)
- Melissa A Toups
- Department of Life and Environmental Sciences, Bournemouth University, Poole, United Kingdom
| | - Beatriz Vicoso
- Institute of Science and Technology Austria, Klosterneuburg, Austria
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3
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Elkrewi M, Khauratovich U, Toups MA, Bett VK, Mrnjavac A, Macon A, Fraisse C, Sax L, Huylmans AK, Hontoria F, Vicoso B. ZW sex-chromosome evolution and contagious parthenogenesis in Artemia brine shrimp. Genetics 2022; 222:6670797. [PMID: 35977389 PMCID: PMC9526061 DOI: 10.1093/genetics/iyac123] [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] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2022] [Accepted: 07/18/2022] [Indexed: 11/13/2022] Open
Abstract
Eurasian brine shrimp (genus Artemia) have closely related sexual and asexual lineages of parthenogenetic females, which produce rare males at low frequencies. Although they are known to have ZW chromosomes, these are not well characterized, and it is unclear whether they are shared across the clade. Furthermore, the underlying genetic architecture of the transmission of asexuality, which can occur when rare males mate with closely related sexual females, is not well understood. We produced a chromosome-level assembly for the sexual Eurasian species A. sinica and characterized in detail the pair of sex chromosomes of this species. We combined this new assembly with short-read genomic data for the sexual species A. sp. Kazakhstan and several asexual lineages of A. parthenogenetica, allowing us to perform an in-depth characterization of sex-chromosome evolution across the genus. We identified a small differentiated region of the ZW pair that is shared by all sexual and asexual lineages, supporting the shared ancestry of the sex chromosomes. We also inferred that recombination suppression has spread to larger sections of the chromosome independently in the American and Eurasian lineages. Finally, we took advantage of a rare male, which we backcrossed to sexual females, to explore the genetic basis of asexuality. Our results suggest that parthenogenesis is likely partly controlled by a locus on the Z chromosome, highlighting the interplay between sex determination and asexuality.
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Affiliation(s)
- Marwan Elkrewi
- Institute of Science and Technology Austria, Klosterneuburg, 3400, Austria
| | - Uladzislava Khauratovich
- Institute of Science and Technology Austria, Klosterneuburg, 3400, Austria.,Department of Chromosome Biology, Max Perutz Labs, University of Vienna, 1030, Austria
| | - Melissa A Toups
- Institute of Science and Technology Austria, Klosterneuburg, 3400, Austria.,Department of Life and Environmental Sciences, Faculty of Science and Technology, Bournemouth University, BH12 5BB, UK
| | | | - Andrea Mrnjavac
- Institute of Science and Technology Austria, Klosterneuburg, 3400, Austria
| | - Ariana Macon
- Institute of Science and Technology Austria, Klosterneuburg, 3400, Austria
| | - Christelle Fraisse
- Institute of Science and Technology Austria, Klosterneuburg, 3400, Austria.,CNRS, Univ. Lille, UMR 8198-Evo-Eco-Paleo, F-59000 Lille, France
| | - Luca Sax
- Institute of Science and Technology Austria, Klosterneuburg, 3400, Austria.,Lewis and Clark College, Portland, OR 97219, USA
| | - Ann Kathrin Huylmans
- Institute of Science and Technology Austria, Klosterneuburg, 3400, Austria.,Institute of Organismic and Molecular Evolution, Johannes Guttenberg Universität Mainz, Mainz, 55122, Germany
| | - Francisco Hontoria
- Instituto de Acuicultura de Torre de la Sal (IATS-CSIC), Ribera de Cabanes, 12595, Spain
| | - Beatriz Vicoso
- Institute of Science and Technology Austria, Klosterneuburg, 3400, Austria
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4
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Abstract
Sewall Wright developed FST for describing population differentiation and it has since been extended to many novel applications, including the detection of homomorphic sex chromosomes. However, there has been confusion regarding the expected estimate of FST for a fixed difference between the X- and Y-chromosome when comparing males and females. Here, we attempt to resolve this confusion by contrasting two common FST estimators and explain why they yield different estimates when applied to the case of sex chromosomes. We show that this difference is true for many allele frequencies, but the situation characterized by fixed differences between the X- and Y-chromosome is among the most extreme. To avoid additional confusion, we recommend that all authors using FST clearly state which estimator of FST their work uses.
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Affiliation(s)
| | - Melissa A. Toups
- Institute of Science and Technology AustriaKlosterneuburgAustria
| | - Beatriz Vicoso
- Institute of Science and Technology AustriaKlosterneuburgAustria
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5
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Huylmans AK, Toups MA, Macon A, Gammerdinger WJ, Vicoso B. Sex-Biased Gene Expression and Dosage Compensation on the Artemia franciscana Z-Chromosome. Genome Biol Evol 2019; 11:1033-1044. [PMID: 30865260 PMCID: PMC6456005 DOI: 10.1093/gbe/evz053] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [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] [Accepted: 03/12/2019] [Indexed: 12/25/2022] Open
Abstract
Males and females of Artemia franciscana, a crustacean commonly used in the aquarium trade, are highly dimorphic. Sex is determined by a pair of ZW chromosomes, but the nature and extent of differentiation of these chromosomes is unknown. Here, we characterize the Z chromosome by detecting genomic regions that show lower genomic coverage in female than in male samples, and regions that harbor an excess of female-specific SNPs. We detect many Z-specific genes, which no longer have homologs on the W, but also Z-linked genes that appear to have diverged very recently from their existing W-linked homolog. We assess patterns of male and female expression in two tissues with extensive morphological dimorphism, gonads, and heads. In agreement with their morphology, sex-biased expression is common in both tissues. Interestingly, the Z chromosome is not enriched for sex-biased genes, and seems to in fact have a mechanism of dosage compensation that leads to equal expression in males and in females. Both of these patterns are contrary to most ZW systems studied so far, making A. franciscana an excellent model for investigating the interplay between the evolution of sexual dimorphism and dosage compensation, as well as Z chromosome evolution in general.
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Affiliation(s)
| | - Melissa A Toups
- Institute of Science and Technology Austria, Klosterneuburg, Austria
| | - Ariana Macon
- Institute of Science and Technology Austria, Klosterneuburg, Austria
| | | | - Beatriz Vicoso
- Institute of Science and Technology Austria, Klosterneuburg, Austria
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6
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Cossard GG, Toups MA, Pannell JR. Sexual dimorphism and rapid turnover in gene expression in pre-reproductive seedlings of a dioecious herb. Ann Bot 2019; 123:1119-1131. [PMID: 30289430 PMCID: PMC6612945 DOI: 10.1093/aob/mcy183] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Accepted: 09/06/2018] [Indexed: 05/06/2023]
Abstract
BACKGROUND AND AIMS Sexual dimorphism in morphology, physiology or life history traits is common in dioecious plants at reproductive maturity, but it is typically inconspicuous or absent in juveniles. Although plants of different sexes probably begin to diverge in gene expression both before their reproduction commences and before dimorphism becomes readily apparent, to our knowledge transcriptome-wide differential gene expression has yet to be demonstrated for any angiosperm species. METHODS The present study documents differences in gene expression in both above- and below-ground tissues of early pre-reproductive individuals of the wind-pollinated dioecious annual herb, Mercurialis annua, which otherwise shows clear sexual dimorphism only at the adult stage. KEY RESULTS Whereas males and females differed in their gene expression at the first leaf stage, sex-biased gene expression peaked just prior to, and after, flowering, as might be expected if sexual dimorphism is partly a response to differential costs of reproduction. Sex-biased genes were over-represented among putative sex-linked genes in M. annua but showed no evidence for more rapid evolution than unbiased genes. CONCLUSIONS Sex-biased gene expression in M. annua occurs as early as the first whorl of leaves is produced, is highly dynamic during plant development and varies substantially between vegetative tissues.
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Affiliation(s)
- Guillaume G Cossard
- Department of Ecology and Evolution, Biophore Building, University of Lausanne, Lausanne, Switzerland
| | - Melissa A Toups
- Department of Ecology and Evolution, Biophore Building, University of Lausanne, Lausanne, Switzerland
- Institute of Science and Technology Austria, Klosterneuburg, Austria
| | - John R Pannell
- Department of Ecology and Evolution, Biophore Building, University of Lausanne, Lausanne, Switzerland
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7
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Veltsos P, Ridout KE, Toups MA, González-Martínez SC, Muyle A, Emery O, Rastas P, Hudzieczek V, Hobza R, Vyskot B, Marais GAB, Filatov DA, Pannell JR. Early Sex-Chromosome Evolution in the Diploid Dioecious Plant Mercurialis annua. Genetics 2019; 212:815-835. [PMID: 31113811 PMCID: PMC6614902 DOI: 10.1534/genetics.119.302045] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2019] [Accepted: 05/13/2019] [Indexed: 12/30/2022] Open
Abstract
Suppressed recombination allows divergence between homologous sex chromosomes and the functionality of their genes. Here, we reveal patterns of the earliest stages of sex-chromosome evolution in the diploid dioecious herb Mercurialis annua on the basis of cytological analysis, de novo genome assembly and annotation, genetic mapping, exome resequencing of natural populations, and transcriptome analysis. The genome assembly contained 34,105 expressed genes, of which 10,076 were assigned to linkage groups. Genetic mapping and exome resequencing of individuals across the species range both identified the largest linkage group, LG1, as the sex chromosome. Although the sex chromosomes of M. annua are karyotypically homomorphic, we estimate that about one-third of the Y chromosome, containing 568 transcripts and spanning 22.3 cM in the corresponding female map, has ceased recombining. Nevertheless, we found limited evidence for Y-chromosome degeneration in terms of gene loss and pseudogenization, and most X- and Y-linked genes appear to have diverged in the period subsequent to speciation between M. annua and its sister species M. huetii, which shares the same sex-determining region. Taken together, our results suggest that the M. annua Y chromosome has at least two evolutionary strata: a small old stratum shared with M. huetii, and a more recent larger stratum that is probably unique to M. annua and that stopped recombining ∼1 MYA. Patterns of gene expression within the nonrecombining region are consistent with the idea that sexually antagonistic selection may have played a role in favoring suppressed recombination.
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Affiliation(s)
- Paris Veltsos
- Department of Biology, Indiana University, Bloomington, IN 47405
- Department of Ecology and Evolution, University of Lausanne, CH-1015, Switzerland
| | - Kate E Ridout
- Department of Ecology and Evolution, University of Lausanne, CH-1015, Switzerland
- Department of Plant Sciences, University of Oxford, OX1 3RB, United Kingdom
- Department of Oncology, John Radcliffe Hospital, Oxford OX3 9DU, United Kingdom
| | - Melissa A Toups
- Department of Ecology and Evolution, University of Lausanne, CH-1015, Switzerland
- Department of Integrative Biology, University of Texas, Austin, 78712 Texas
| | | | - Aline Muyle
- Laboratoire Biométrie et Biologie Évolutive (UMR 5558), CNRS/Université Lyon 1, 69100 Villeurbanne, France
| | - Olivier Emery
- Department of Ecology and Evolution, University of Lausanne, CH-1015, Switzerland
| | - Pasi Rastas
- University of Helsinki, Institute of Biotechnology, 00014, Finland
| | - Vojtech Hudzieczek
- Department of Plant Developmental Genetics, Institute of Biophysics, Academy of Sciences of the Czech Republic, 61200 Brno, Czech Republic
| | - Roman Hobza
- Department of Plant Developmental Genetics, Institute of Biophysics, Academy of Sciences of the Czech Republic, 61200 Brno, Czech Republic
| | - Boris Vyskot
- Department of Plant Developmental Genetics, Institute of Biophysics, Academy of Sciences of the Czech Republic, 61200 Brno, Czech Republic
| | | | - Dmitry A Filatov
- Department of Plant Sciences, University of Oxford, OX1 3RB, United Kingdom
| | - John R Pannell
- Department of Ecology and Evolution, University of Lausanne, CH-1015, Switzerland
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8
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Toups MA, Rodrigues N, Perrin N, Kirkpatrick M. A reciprocal translocation radically reshapes sex-linked inheritance in the common frog. Mol Ecol 2019; 28:1877-1889. [PMID: 30576024 DOI: 10.1111/mec.14990] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2018] [Revised: 12/04/2018] [Accepted: 12/04/2018] [Indexed: 12/22/2022]
Abstract
X and Y chromosomes can diverge when rearrangements block recombination between them. Here we present the first genomic view of a reciprocal translocation that causes two physically unconnected pairs of chromosomes to be coinherited as sex chromosomes. In a population of the common frog (Rana temporaria), both pairs of X and Y chromosomes show extensive sequence differentiation, but not degeneration of the Y chromosomes. A new method based on gene trees shows both chromosomes are sex-linked. Furthermore, the gene trees from the two Y chromosomes have identical topologies, showing they have been coinherited since the reciprocal translocation occurred. Reciprocal translocations can thus reshape sex linkage on a much greater scale compared with inversions, the type of rearrangement that is much better known in sex chromosome evolution, and they can greatly amplify the power of sexually antagonistic selection to drive genomic rearrangement. Two more populations show evidence of other rearrangements, suggesting that this species has unprecedented structural polymorphism in its sex chromosomes.
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Affiliation(s)
- Melissa A Toups
- Department of Integrative Biology, University of Texas, Austin, Texas.,Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
| | - Nicolas Rodrigues
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
| | - Nicolas Perrin
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
| | - Mark Kirkpatrick
- Department of Integrative Biology, University of Texas, Austin, Texas
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9
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Ma WJ, Veltsos P, Toups MA, Rodrigues N, Sermier R, Jeffries DL, Perrin N. Tissue Specificity and Dynamics of Sex-Biased Gene Expression in a Common Frog Population with Differentiated, Yet Homomorphic, Sex Chromosomes. Genes (Basel) 2018; 9:E294. [PMID: 29895802 PMCID: PMC6027210 DOI: 10.3390/genes9060294] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [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: 04/26/2018] [Revised: 06/04/2018] [Accepted: 06/11/2018] [Indexed: 02/06/2023] Open
Abstract
Sex-biased genes are central to the study of sexual selection, sexual antagonism, and sex chromosome evolution. We describe a comprehensive de novo assembled transcriptome in the common frog Rana temporaria based on five developmental stages and three adult tissues from both sexes, obtained from a population with karyotypically homomorphic but genetically differentiated sex chromosomes. This allows the study of sex-biased gene expression throughout development, and its effect on the rate of gene evolution while accounting for pleiotropic expression, which is known to negatively correlate with the evolutionary rate. Overall, sex-biased genes had little overlap among developmental stages and adult tissues. Late developmental stages and gonad tissues had the highest numbers of stage- or tissue-specific genes. We find that pleiotropic gene expression is a better predictor than sex bias for the evolutionary rate of genes, though it often interacts with sex bias. Although genetically differentiated, the sex chromosomes were not enriched in sex-biased genes, possibly due to a very recent arrest of XY recombination. These results extend our understanding of the developmental dynamics, tissue specificity, and genomic localization of sex-biased genes.
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Affiliation(s)
- Wen-Juan Ma
- Department of Ecology and Evolution, University of Lausanne, CH 1015 Lausanne, Switzerland.
| | - Paris Veltsos
- Department of Ecology and Evolution, University of Lausanne, CH 1015 Lausanne, Switzerland.
- Department of Biology, Indiana University, Jordan Hall, 1001 East Third Street, Bloomington, IN 47405, USA.
| | - Melissa A Toups
- Department of Ecology and Evolution, University of Lausanne, CH 1015 Lausanne, Switzerland.
- Institute of Science and Technology Austria, Am Campus 1, 3400 Klosterneuburg, Austria.
| | - Nicolas Rodrigues
- Department of Ecology and Evolution, University of Lausanne, CH 1015 Lausanne, Switzerland.
| | - Roberto Sermier
- Department of Ecology and Evolution, University of Lausanne, CH 1015 Lausanne, Switzerland.
| | - Daniel L Jeffries
- Department of Ecology and Evolution, University of Lausanne, CH 1015 Lausanne, Switzerland.
| | - Nicolas Perrin
- Department of Ecology and Evolution, University of Lausanne, CH 1015 Lausanne, Switzerland.
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Ascunce MS, Toups MA, Kassu G, Fane J, Scholl K, Reed DL. Nuclear genetic diversity in human lice (Pediculus humanus) reveals continental differences and high inbreeding among worldwide populations. PLoS One 2013; 8:e57619. [PMID: 23460886 PMCID: PMC3583987 DOI: 10.1371/journal.pone.0057619] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2012] [Accepted: 01/24/2013] [Indexed: 11/19/2022] Open
Abstract
Understanding the evolution of parasites is important to both basic and applied evolutionary biology. Knowledge of the genetic structure of parasite populations is critical for our ability to predict how an infection can spread through a host population and for the design of effective control methods. However, very little is known about the genetic structure of most human parasites, including the human louse (Pediculus humanus). This species is composed of two ecotypes: the head louse (Pediculus humanus capitis De Geer), and the clothing (body) louse (Pediculus humanus humanus Linnaeus). Hundreds of millions of head louse infestations affect children every year, and this number is on the rise, in part because of increased resistance to insecticides. Clothing lice affect mostly homeless and refugee-camp populations and although they are less prevalent than head lice, the medical consequences are more severe because they vector deadly bacterial pathogens. In this study we present the first assessment of the genetic structure of human louse populations by analyzing the nuclear genetic variation at 15 newly developed microsatellite loci in 93 human lice from 11 sites in four world regions. Both ecotypes showed heterozygote deficits relative to Hardy-Weinberg equilibrium and high inbreeding values, an expected pattern given their parasitic life history. Bayesian clustering analyses assigned lice to four distinct genetic clusters that were geographically structured. The low levels of gene flow among louse populations suggested that the evolution of insecticide resistance in lice would most likely be affected by local selection pressures, underscoring the importance of tailoring control strategies to population-specific genetic makeup and evolutionary history. Our panel of microsatellite markers provides powerful data to investigate not only ecological and evolutionary processes in lice, but also those in their human hosts because of the long-term coevolutionary association between lice and humans.
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Affiliation(s)
- Marina S Ascunce
- Florida Museum of Natural History, University of Florida, Gainesville, Florida, United States of America.
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11
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Abstract
Most of our knowledge of sex-chromosome evolution comes from male heterogametic (XX/XY) taxa. With the genome sequencing of multiple female heterogametic (ZZ/ZW) taxa, we can now ask whether there are patterns of evolution common to both sex chromosome systems. In all XX/XY systems examined to date, there is an excess of testis-biased retrogenes moving from the X chromosome to the autosomes, which is hypothesized to result from either sexually antagonistic selection or escape from meiotic sex chromosome inactivation (MSCI). We examined RNA-mediated (retrotransposed) and DNA-mediated gene movement in two independently evolved ZZ/ZW systems, birds (chicken and zebra finch) and lepidopterans (silkworm). Even with sexually antagonistic selection likely operating in both taxa and MSCI having been identified in the chicken, we find no evidence for an excess of genes moving from the Z chromosome to the autosomes in either lineage. We detected no excess for either RNA- or DNA-mediated duplicates, across a range of approaches and methods. We offer some potential explanations for this difference between XX/XY and ZZ/ZW sex chromosome systems, but further work is needed to distinguish among these hypotheses. Regardless of the root causes, we have identified an additional, potentially inherent, difference between XX/XY and ZZ/ZW systems.
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12
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Abstract
Clothing use is an important modern behavior that contributed to the successful expansion of humans into higher latitudes and cold climates. Previous research suggests that clothing use originated anywhere between 40,000 and 3 Ma, though there is little direct archaeological, fossil, or genetic evidence to support more specific estimates. Since clothing lice evolved from head louse ancestors once humans adopted clothing, dating the emergence of clothing lice may provide more specific estimates of the origin of clothing use. Here, we use a Bayesian coalescent modeling approach to estimate that clothing lice diverged from head louse ancestors at least by 83,000 and possibly as early as 170,000 years ago. Our analysis suggests that the use of clothing likely originated with anatomically modern humans in Africa and reinforces a broad trend of modern human developments in Africa during the Middle to Late Pleistocene.
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Affiliation(s)
- Melissa A. Toups
- Department of Biology, Indiana University
- Department of Biology, University of Florida
| | - Andrew Kitchen
- Department of Biology, The Pennsylvania State University
- Department of Anthropology, University of Florida
| | - Jessica E. Light
- Department of Wildlife and Fisheries Sciences, A&M University
- Florida Museum of Natural History, University of Florida
| | - David L. Reed
- Florida Museum of Natural History, University of Florida
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13
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Abstract
The soil bacterium Myxococcus xanthus is a model for the study of cooperative microbial behaviours such as social motility and fruiting body formation. Several M. xanthus developmental traits that are frequently quantified for laboratory strains are likely to be significant components of fitness in natural populations, yet little is known about the degree to which such traits vary in the wild and may therefore be subject to natural selection. Here, we have tested whether several key M. xanthus developmental life-history traits have diverged significantly among strains both from globally distant origins and from within a sympatric, centimetre-scale population. The isolates examined here were found to vary considerably, in a heritable manner, in their rate of developmental aggregation and in both their rate and efficiency of spore production. Isolates also varied in the nutrient-concentration threshold triggering spore formation and in the heat resistance of spores. The large diversity of developmental phenotypes documented here leads to questions regarding the relative roles of selection and genetic drift in shaping the diversity of local soil populations with respect to these developmental traits. It also raises the question of whether fitness in the wild is largely determined by traits that are expressed independent of social context or by behaviours that are expressed only in genetically heterogeneous social groups.
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14
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Light JE, Toups MA, Reed DL. What's in a name: the taxonomic status of human head and body lice. Mol Phylogenet Evol 2008; 47:1203-16. [PMID: 18434207 DOI: 10.1016/j.ympev.2008.03.014] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2007] [Revised: 01/23/2008] [Accepted: 03/06/2008] [Indexed: 11/27/2022]
Abstract
Human head lice (Anoplura: Pediculidae: Pediculus) are pandemic, parasitizing countless school children worldwide due to the evolution of insecticide resistance, and human body (clothing) lice are responsible for the deaths of millions as a result of vectoring several deadly bacterial pathogens. Despite the obvious impact these lice have had on their human hosts, it is unclear whether head and body lice represent two morphological forms of a single species or two distinct species. To assess the taxonomic status of head and body lice, we provide a synthesis of publicly available molecular data in GenBank, and we compare phylogenetic and population genetic methods using the most diverse geographic and molecular sampling presently available. Our analyses find reticulated networks, gene flow, and a lack of reciprocal monophyly, all of which indicate that head and body lice do not represent genetically distinct evolutionary units. Based on these findings, as well as inconsistencies of morphological, behavioral, and ecological variability between head and body lice, we contend that no known species concept would recognize these louse morphotypes as separate species. We recommend recognizing head and body lice as morphotypes of a single species, Pediculus humanus, until compelling new data and analyses (preferably analyses of fast evolving nuclear markers in a coalescent framework) indicate otherwise.
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Affiliation(s)
- Jessica E Light
- Florida Museum of Natural History, University of Florida, Dickinson Hall, PO Box 117800, Gainesville, FL 32611-7800, USA.
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