1
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Cádiz MI, Tengstedt ANB, Sørensen IH, Pedersen ES, Fox AD, Hansen MM. Demographic History and Inbreeding in Two Declining Sea Duck Species Inferred From Whole-Genome Sequence Data. Evol Appl 2024; 17:e70008. [PMID: 39257569 PMCID: PMC11386304 DOI: 10.1111/eva.70008] [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: 05/11/2024] [Revised: 08/16/2024] [Accepted: 08/19/2024] [Indexed: 09/12/2024] Open
Abstract
Anthropogenic impact has transitioned from threatening already rare species to causing significant declines in once numerous organisms. Long-tailed duck (Clangula hyemalis) and velvet scoter (Melanitta fusca) were once important quarry sea duck species in NW Europe, but recent declines resulted in their reclassification as vulnerable on the IUCN Red List. We sequenced and assembled genomes for both species and resequenced 15 individuals of each. Using analyses based on site frequency spectra and sequential Markovian coalescence, we found C. hyemalis to show more historical demographic stability, whereas M. fusca was affected particularly by the Last (Weichselian) Glaciation. This likely reflects C. hyemalis breeding continuously across the Arctic, with cycles of glaciation primarily shifting breeding areas south or north without major population declines, whereas the more restricted southern range of M. fusca would lead to significant range contraction during glaciations. Both species showed evidence of declines over the past thousands of years, potentially reflecting anthropogenic pressures with the recent decline indicating an accelerated process. Analysis of runs of homozygosity (ROH) showed low but nontrivial inbreeding, with F ROH from 0.012 to 0.063 in C. hyemalis and ranging from 0 to 0.047 in M. fusca. Lengths of ROH suggested that this was due to ongoing background inbreeding rather than recent declines. Overall, despite demographically important declines, this has not yet led to strong inbreeding and genetic erosion, and the most pressing conservation concern may be the risk of density-dependent (Allee) effects. We recommend monitoring of inbreeding using ROH analysis as a cost-efficient method to track future developments to support effective conservation of these species.
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Affiliation(s)
- María I Cádiz
- Department of Biology Aarhus University Aarhus Denmark
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2
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Liu YF, Li YL, Xing TF, Xue DX, Liu JX. Genetic architecture of long-distance migration and population genomics of the endangered Japanese eel. iScience 2024; 27:110563. [PMID: 39165844 PMCID: PMC11334786 DOI: 10.1016/j.isci.2024.110563] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2024] [Revised: 06/21/2024] [Accepted: 07/18/2024] [Indexed: 08/22/2024] Open
Abstract
The Japanese eel (Anguilla japonica), a flagship anguillid species for conservation, is known for its long-distance-oriented migration. However, our understanding of the genetic architecture underlying long-distance migration and population genomic characteristics of A. japonica is still limited. Here, we generated a high-quality chromosome-level genome assembly and conducted whole-genome resequencing of 218 individuals to explore these aspects. Strong signals of selection were found on genes involved in long-distance aerobic exercise and navigation, which might be associated with evolutionary adaptation to long-distance migrations. Low genetic diversity was detected, which might result from genetic drift associated with demographic declines. Both mitochondrial and nuclear genomic datasets supported the existence of a single panmictic population for Japanese eel, despite signals of single-generation selection. Candidate genes for local selection involved in functions like development and circadian rhythm. The findings can provide insights to adaptative evolution to long-distance migration and inform conservation efforts for A. japonica.
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Affiliation(s)
- Yan-Fang Liu
- CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
- Laboratory for Marine Ecology and Environmental Science, Qingdao Marine Science and Technology Center, Qingdao 266237, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yu-Long Li
- CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
- Laboratory for Marine Ecology and Environmental Science, Qingdao Marine Science and Technology Center, Qingdao 266237, China
| | - Teng-Fei Xing
- CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
- Laboratory for Marine Ecology and Environmental Science, Qingdao Marine Science and Technology Center, Qingdao 266237, China
| | - Dong-Xiu Xue
- CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
- Laboratory for Marine Ecology and Environmental Science, Qingdao Marine Science and Technology Center, Qingdao 266237, China
| | - Jin-Xian Liu
- CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
- Laboratory for Marine Ecology and Environmental Science, Qingdao Marine Science and Technology Center, Qingdao 266237, China
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3
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Schmid S, Bachmann Salvy M, Garcia Jimenez A, Bertrand JAM, Cortesi F, Heim S, Huyghe F, Litsios G, Marcionetti A, O'Donnell JL, Riginos C, Tettamanti V, Salamin N. Gene flow throughout the evolutionary history of a colour polymorphic and generalist clownfish. Mol Ecol 2024; 33:e17436. [PMID: 38872589 DOI: 10.1111/mec.17436] [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: 11/07/2023] [Revised: 05/12/2024] [Accepted: 05/17/2024] [Indexed: 06/15/2024]
Abstract
Even seemingly homogeneous on the surface, the oceans display high environmental heterogeneity across space and time. Indeed, different soft barriers structure the marine environment, which offers an appealing opportunity to study various evolutionary processes such as population differentiation and speciation. Here, we focus on Amphiprion clarkii (Actinopterygii; Perciformes), the most widespread of clownfishes that exhibits the highest colour polymorphism. Clownfishes can only disperse during a short pelagic larval phase before their sedentary adult lifestyle, which might limit connectivity among populations, thus facilitating speciation events. Consequently, the taxonomic status of A. clarkii has been under debate. We used whole-genome resequencing data of 67 A. clarkii specimens spread across the Indian and Pacific Oceans to characterize the species' population structure, demographic history and colour polymorphism. We found that A. clarkii spread from the Indo-Pacific Ocean to the Pacific and Indian Oceans following a stepping-stone dispersal and that gene flow was pervasive throughout its demographic history. Interestingly, colour patterns differed noticeably among the Indonesian populations and the two populations at the extreme of the sampling distribution (i.e. Maldives and New Caledonia), which exhibited more comparable colour patterns despite their geographic and genetic distances. Our study emphasizes how whole-genome studies can uncover the intricate evolutionary past of wide-ranging species with diverse phenotypes, shedding light on the complex nature of the species concept paradigm.
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Affiliation(s)
- Sarah Schmid
- Department of Computational Biology, University of Lausanne, Lausanne, Switzerland
| | | | | | - Joris A M Bertrand
- Department of Computational Biology, University of Lausanne, Lausanne, Switzerland
| | - Fabio Cortesi
- Queensland Brain Institute, the University of Queensland, Brisbane, Queensland, Australia
- School of the Environment, The University of Queensland, Brisbane, Queensland, Australia
| | - Sara Heim
- Department of Computational Biology, University of Lausanne, Lausanne, Switzerland
| | - Filip Huyghe
- Marine Biology Laboratory, Department of Ecology and Biodiversity, Vrije Universiteit Brussel, Brussel, Belgium
| | - Glenn Litsios
- Department of Computational Biology, University of Lausanne, Lausanne, Switzerland
| | - Anna Marcionetti
- Department of Computational Biology, University of Lausanne, Lausanne, Switzerland
| | - James L O'Donnell
- Department of Ecology and Evolutionary Biology, University of California Santa Cruz, Santa Cruz, California, USA
| | - Cynthia Riginos
- School of the Environment, The University of Queensland, Brisbane, Queensland, Australia
| | - Valerio Tettamanti
- Queensland Brain Institute, the University of Queensland, Brisbane, Queensland, Australia
| | - Nicolas Salamin
- Department of Computational Biology, University of Lausanne, Lausanne, Switzerland
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4
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Ely T, Patten N, Naisbett-Jones LC, Spencer ET, Willette DA, Marko PB. Molecular identification of critically endangered European eels ( Anguilla anguilla) in US retail outlets. PeerJ 2023; 11:e14531. [PMID: 36778145 PMCID: PMC9910185 DOI: 10.7717/peerj.14531] [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: 06/27/2022] [Accepted: 11/16/2022] [Indexed: 02/08/2023] Open
Abstract
The European eel (Anguilla anguilla) has declined by over 90% since the early 1980s and has been listed as critically endangered. Yet, despite strict export bans from the European Union, the European eel is still sold illegally in many countries. Efforts to monitor the trade of European eels have been primarily concentrated in Asian markets where concerningly high rates of European eel have been reported. Comparably fewer studies have assessed the identities of eel samples from the United States (US), despite the obvious implications for eel conservation. To address this knowledge gap, we purchased 137 eel products (134 freshwater eels and three saltwater eels) from grocers, sushi bars, and restaurants in nine states across the US from 2019 to 2021. Seven samples (5.2%) labeled as freshwater eels (or "unagi") were identified as European eels using a combination of mitochondrial (cytochrome b) and nuclear (18S rRNA) restriction digestion assays, a fast and inexpensive molecular tool for seafood identification that can identify hybrids between European eels (A. anguilla) and American eels (A. rostrata). No hybrids between European and American eels were found and all seven samples identified with restriction digestion as European eels were confirmed by sequencing of cytochrome b and 18S rRNA. Frequency of European eels in US markets did not significantly correlate with state or retail type. Although illegal eel exports are likely reaching US consumers, the frequency of European eel samples in this study of the US market is much lower than found in other non-European countries.
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Affiliation(s)
- Taylor Ely
- School of Life Sciences, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i, United States of America
| | - Nathaniel Patten
- School of Life Sciences, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i, United States of America
| | - Lewis C. Naisbett-Jones
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States of America
| | - Erin T. Spencer
- Department of Biological Sciences, Florida International University, Miami, FL, United States of America
| | - Demian A. Willette
- Biology Department, Loyola Marymount University, Los Angeles, CA, United States of America
| | - Peter B. Marko
- School of Life Sciences, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i, United States of America
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5
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Demographic history of two endangered Atlantic eel species, Anguilla anguilla and Anguilla rostrata. CONSERV GENET 2022. [DOI: 10.1007/s10592-022-01469-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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6
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Liu S, Tengstedt ANB, Jacobsen MW, Pujolar JM, Jónsson B, Lobón-Cervià J, Bernatchez L, Hansen MM. Genome-wide methylation in the panmictic European eel (Anguilla anguilla). Mol Ecol 2022; 31:4286-4306. [PMID: 35767387 DOI: 10.1111/mec.16586] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2022] [Revised: 06/21/2022] [Accepted: 06/27/2022] [Indexed: 11/30/2022]
Abstract
The role of methylation in adaptive, developmental and speciation processes has attracted considerable interest, but interpretation of results is complicated by diffuse boundaries between genetic and non-genetic variation. We studied whole genome genetic and methylation variation in the European eel, distributed from subarctic to subtropical environments, but with panmixia precluding genetically based local adaptation beyond single-generation responses. Overall methylation was 70.9%, with hypomethylation predominantly found in promoters and first exons. Redundancy analyses involving juvenile glass eels showed 0.06% and 0.03% of the variance at SNPs to be explained by localities and environmental variables, respectively, with GO terms of genes associated with outliers primarily involving neural system functioning. For CpGs 2.98% and 1.36% of variance was explained by localities and environmental variables. Differentially methylated regions particularly included genes involved in developmental processes, with hox clusters featuring prominently. Life stage (adult versus glass eels) was the most important source of inter-individual variation in methylation, likely reflecting both ageing and developmental processes. Demethylation of transposable elements relative to pure European eel was observed in European X American eel hybrids, possibly representing postzygotic barriers in this system characterized by prolonged speciation and ongoing gene flow. Whereas the genetic data are consistent with a role of single-generation selective responses, the methylation results underpin the importance of epigenetics in the life cycle of eels and suggests interactions between local environments, development and phenotypic variation mediated by methylation variation. Eels are remarkable by having retained eight hox clusters, and the results suggest important roles of methylation at hox genes for adaptive processes.
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Affiliation(s)
- Shenglin Liu
- Department of Biology, Aarhus University, Aarhus, Denmark
| | | | - Magnus W Jacobsen
- Section for Marine Living Resources, National Institute of Aquatic Resources, Technical University of Denmark, Silkeborg, Denmark
| | - Jose Martin Pujolar
- Centre for Gelatinous Plankton Ecology and Evolution, National Institute of Aquatic Resources, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Bjarni Jónsson
- North West Iceland Nature Center, Iceland.,The Icelandic Parliament, Reykjavík, Iceland
| | | | - Louis Bernatchez
- IBIS (Institut de Biologie Intégrative et des Systèmes), Université Laval, Québec, Canada
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7
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Chang JT, Chao CT, Nakamura K, Liu HL, Luo MX, Liao PC. Divergence With Gene Flow and Contrasting Population Size Blur the Species Boundary in Cycas Sect. Asiorientales, as Inferred From Morphology and RAD-Seq Data. FRONTIERS IN PLANT SCIENCE 2022; 13:824158. [PMID: 35615129 PMCID: PMC9125193 DOI: 10.3389/fpls.2022.824158] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Accepted: 03/15/2022] [Indexed: 06/15/2023]
Abstract
The divergence process of incipient species is fascinating but elusive by incomplete lineage sorting or gene flow. Species delimitation is also challenging among those morphologically similar allopatric species, especially when lacking comprehensive data. Cycas sect. Asiorientales, comprised of C. taitungensis and C. revoluta in the Ryukyu Archipelago and Taiwan, diverged recently with continuous gene flow, resulting in a reciprocal paraphyletic relationship. Their previous evolutionary inferences are questioned from few genetic markers, incomplete sampling, and incomprehensive morphological comparison by a long-term taxonomic misconception. By whole range sampling, this study tests the geographic mode of speciation in the two species of Asiorientales by approximate Bayesian computation (ABC) using genome-wide single nucleotide polymorphisms (SNPs). The individual tree was reconstructed to delimit the species and track the gene-flow trajectory. With the comparison of diagnostic morphological traits and genetic data, the allopatric speciation was rejected. Alternatively, continuous but spatially heterogeneous gene flow driven by transoceanic vegetative dispersal and pollen flow with contrasting population sizes blurred their species boundary. On the basis of morphological, genetic, and evolutionary evidence, we synonymized these two Cycas species. This study highlights not only the importance of the Kuroshio Current to species evolution but also the disadvantage of using species with geographically structured genealogies as conservation units.
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Affiliation(s)
- Jui-Tse Chang
- School of Life Science, National Taiwan Normal University, Taipei, Taiwan
| | - Chien-Ti Chao
- School of Life Science, National Taiwan Normal University, Taipei, Taiwan
| | - Koh Nakamura
- Botanic Garden, Field Science Center for Northern Biosphere, Hokkaido University, Sapporo, Japan
| | - Hsiao-Lei Liu
- Department of Anthropology, Smithsonian Institution, National Museum of Natural History, Washington, DC, United States
| | - Min-Xin Luo
- School of Life Science, National Taiwan Normal University, Taipei, Taiwan
| | - Pei-Chun Liao
- School of Life Science, National Taiwan Normal University, Taipei, Taiwan
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8
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Pujolar JM, Jacobsen MW, Bertolini F. Comparative genomics and signatures of selection in North Atlantic eels. Mar Genomics 2022; 62:100933. [PMID: 35182837 DOI: 10.1016/j.margen.2022.100933] [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: 11/11/2021] [Revised: 02/04/2022] [Accepted: 02/04/2022] [Indexed: 11/17/2022]
Abstract
Comparative genomic approaches can identify putative private and shared signatures of selection. We performed a comparative genomic study of North Atlantic eels, European eel (Anguilla Anguilla) and American eel (A. rostrata). The two sister species are nearly undistinguishable at the phenotypic level and despite a wide non-overlapping continental distribution, they spawn in partial sympatry in the Sargasso Sea. Taking advantage of the newly assembled and annotated genome, we used genome wide RAD sequencing data of 359 individuals retrieved from Sequence Nucleotide Archive and state-of-the-art statistic tests to identify putative genomic signatures of selection in North Atlantic eels. First, using the FST and XP-EHH methods, we detected apparent islands of divergence on a total of 7 chromosomes, particularly on chromosomes 6 and 10. Gene ontology analyses suggested candidate genes mainly related to energy production, development and regulation, which could reflect strong selection on traits related to eel migration and larval duration time. Gene effect prediction using SNPeff showed a high number of SNPs in noncoding regions, pointing to a possible regulatory role. Second, using the iHS method we detected shared regions under selection on a total of 11 chromosomes. Several hypotheses might account for the detection of shared islands of selection in North Atlantic eels, including parallel evolution due to adaptation to similar environments and introgression. Future comparative genomic studies will be needed to further clarify the causes and consequences of introgression, including the directionality of these introgression events.
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Affiliation(s)
- Jose Martin Pujolar
- Centre for Gelatinous Plankton Ecology and Evolution, National Institute of Aquatic Resources, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Magnus Wulff Jacobsen
- Section for Marine Living Resources, National Institute of Aquatic Resources, Technical University of Denmark, Silkeborg, Denmark
| | - Francesca Bertolini
- Section for Marine Living Resources, National Institute of Aquatic Resources, Technical University of Denmark, Kongens Lyngby, Denmark.
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9
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Vilaça ST, Piccinno R, Rota‐Stabelli O, Gabrielli M, Benazzo A, Matschiner M, Soares LS, Bolten AB, Bjorndal KA, Bertorelle G. Divergence and hybridization in sea turtles: Inferences from genome data show evidence of ancient gene flow between species. Mol Ecol 2021; 30:6178-6192. [PMID: 34390061 PMCID: PMC9292604 DOI: 10.1111/mec.16113] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2021] [Accepted: 07/26/2021] [Indexed: 11/30/2022]
Abstract
Reconstructing past events of hybridization and population size changes are required to understand speciation mechanisms and current patterns of genetic diversity, and ultimately contribute to species' conservation. Sea turtles are ancient species currently facing anthropogenic threats including climate change, fisheries, and illegal hunting. Five of the seven extant sea turtle species are known to currently hybridize, especially along the Brazilian coast where some populations can have ~32%-42% of hybrids. Although frequently observed today, it is not clear what role hybridization plays in the evolutionary diversification of this group of reptiles. In this study, we generated whole genome resequencing data of the five globally distributed sea turtle species to estimate a calibrated phylogeny and the population size dynamics, and to understand the role of hybridization in shaping the genomes of these ancient species. Our results reveal discordant species divergence dates between mitochondrial and nuclear genomes, with a high frequency of conflicting trees throughout the nuclear genome suggesting that some sea turtle species frequently hybridized in the past. The reconstruction of the species' demography showed a general decline in effective population sizes with no signs of recovery, except for the leatherback sea turtle. Furthermore, we discuss the influence of reference bias in our estimates. We show long-lasting ancestral gene flow events within Chelonioidea that continued for millions of years after initial divergence. Speciation with gene flow is a common pattern in marine species, and it raises questions whether current hybridization events should be considered as a part of these species' evolutionary history or a conservation issue.
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Affiliation(s)
| | - Riccardo Piccinno
- Department of Sustainable Agro‐ecosystems and BioresourcesFondazione Edmund MachTrentoItaly
| | - Omar Rota‐Stabelli
- Department of Sustainable Agro‐ecosystems and BioresourcesFondazione Edmund MachTrentoItaly
| | - Maëva Gabrielli
- Department of Life Sciences and BiotechnologyUniversity of FerraraFerraraItaly
| | - Andrea Benazzo
- Department of Life Sciences and BiotechnologyUniversity of FerraraFerraraItaly
| | | | - Luciano S. Soares
- Archie Carr Center for Sea Turtle Research and Department of BiologyUniversity of FloridaGainesvilleFLUSA
| | - Alan B. Bolten
- Archie Carr Center for Sea Turtle Research and Department of BiologyUniversity of FloridaGainesvilleFLUSA
| | - Karen A. Bjorndal
- Archie Carr Center for Sea Turtle Research and Department of BiologyUniversity of FloridaGainesvilleFLUSA
| | - Giorgio Bertorelle
- Department of Life Sciences and BiotechnologyUniversity of FerraraFerraraItaly
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10
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Abstract
Diadromy, the predictable movements of individuals between marine and freshwater environments, is biogeographically and phylogenetically widespread across fishes. Thus, despite the high energetic and potential fitness costs involved in moving between distinct environments, diadromy appears to be an effective life history strategy. Yet, the origin and molecular mechanisms that underpin this migratory behavior are not fully understood. In this review, we aim first to summarize what is known about diadromy in fishes; this includes the phylogenetic relationship among diadromous species, a description of the main hypotheses regarding its origin, and a discussion of the presence of non-migratory populations within diadromous species. Second, we discuss how recent research based on -omics approaches (chiefly genomics, transcriptomics, and epigenomics) is beginning to provide answers to questions on the genetic bases and origin(s) of diadromy. Finally, we suggest future directions for -omics research that can help tackle questions on the evolution of diadromy.
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Affiliation(s)
- M. Lisette Delgado
- Department of Biology, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada
| | - Daniel E. Ruzzante
- Department of Biology, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada
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11
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Barth JMI, Gubili C, Matschiner M, Tørresen OK, Watanabe S, Egger B, Han YS, Feunteun E, Sommaruga R, Jehle R, Schabetsberger R. Stable species boundaries despite ten million years of hybridization in tropical eels. Nat Commun 2020; 11:1433. [PMID: 32188850 PMCID: PMC7080837 DOI: 10.1038/s41467-020-15099-x] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2019] [Accepted: 02/07/2020] [Indexed: 02/01/2023] Open
Abstract
Genomic evidence is increasingly underpinning that hybridization between taxa is commonplace, challenging our views on the mechanisms that maintain their boundaries. Here, we focus on seven catadromous eel species (genus Anguilla) and use genome-wide sequence data from more than 450 individuals sampled across the tropical Indo-Pacific, morphological information, and three newly assembled draft genomes to compare contemporary patterns of hybridization with signatures of past introgression across a time-calibrated phylogeny. We show that the seven species have remained distinct for up to 10 million years and find that the current frequencies of hybridization across species pairs contrast with genomic signatures of past introgression. Based on near-complete asymmetry in the directionality of hybridization and decreasing frequencies of later-generation hybrids, we suggest cytonuclear incompatibilities, hybrid breakdown, and purifying selection as mechanisms that can support species cohesion even when hybridization has been pervasive throughout the evolutionary history of clades.
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Affiliation(s)
- Julia M I Barth
- Department of Environmental Sciences, Zoological Institute, University of Basel, Vesalgasse 1, 4051, Basel, Switzerland
| | - Chrysoula Gubili
- Fisheries Research Institute, Hellenic Agricultural Organisation-DEMETER, Nea Peramos, 64 007, Kavala, Greece
| | - Michael Matschiner
- Department of Palaeontology and Museum, University of Zurich, Karl-Schmid-Strasse 4, 8006, Zurich, Switzerland.
- Centre for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo, P.O. Box 1066 Blindern, 0316, Oslo, Norway.
| | - Ole K Tørresen
- Centre for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo, P.O. Box 1066 Blindern, 0316, Oslo, Norway
| | - Shun Watanabe
- Faculty of Agriculture, Kindai University, 3327-204 Nakamachi, Nara, 631-8505, Japan
| | - Bernd Egger
- Department of Environmental Sciences, Zoological Institute, University of Basel, Vesalgasse 1, 4051, Basel, Switzerland
| | - Yu-San Han
- Institute of Fisheries Science, College of Life Science, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, 10617, Taiwan
| | - Eric Feunteun
- Laboratoire Biologie des Organismes et Écosystèmes Aquatiques (BOREA), Muséum National d'Histoire Naturelle, CNRS, Sorbonne Université, Université de Caen Normandie, Université des Antilles, IRD, 61 Rue Buffon, CP 53, 75231, Paris Cedex 05, France
- MNHN-Station Marine de Dinard, Centre de Recherche et d'Enseignement Sur les Systèmes Côtiers (CRESCO), 38 Rue du Port Blanc, 35800, Dinard, France
| | - Ruben Sommaruga
- Department of Ecology, University of Innsbruck, Technikerstr. 25, 6020, Innsbruck, Austria
| | - Robert Jehle
- School of Science, Engineering and Environment, University of Salford, Salford Crescent, Salford, M5 4WT, UK.
| | - Robert Schabetsberger
- Department of Biosciences, University of Salzburg, Hellbrunnerstrasse 34, 5020, Salzburg, Austria.
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