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Willis AB, Ermolaeva E, Zyck A, Rognstad R, Davis S, Hilbish TJ. Integration of natural selection across the life cycle stabilizes a marine mussel hybrid zone. Ecol Evol 2024; 14:e11086. [PMID: 38469047 PMCID: PMC10925496 DOI: 10.1002/ece3.11086] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2023] [Revised: 02/12/2024] [Accepted: 02/16/2024] [Indexed: 03/13/2024] Open
Abstract
Hybridization among related species is now recognized as common but it remains unclear how hybrid zones persist for prolonged periods. Here, we test the hypothesis that selection in different components of the life cycle may stabilize a hybrid zone. A hybrid zone occurs in southwest England between the marine mussels Mytilus edulis and M. galloprovincialis. Previous studies have found strong directional selection against alleles from M. edulis occurs among hybrids in the adult stage. Traditional hybrid zone models argue that alleles that are selected within the hybrid zone are replaced by migration from neighboring parental population into the hybrid zone. In this system, however, migration occurs out of this hybrid zone into neighboring parental populations. This hybrid zone should therefore be unstable and dissipate, yet this zone has persisted for more than 30 years. We tested and rejected the hypothesis that differences in fecundity may select for M. edulis alleles within this hybrid zone and thus counter the selection observed against these alleles among adults. We also tested the hypothesis that selection during the larval stage may counter selection against M. edulis alleles in the adult stage. We found that selection favors M. edulis alleles during the veliger stage of larval development. The direction and strength of selection during the larval stage are sufficient to counter strong selection during the adult portion of the life cycle. This hybrid zone is stabilized by opposing forms of directional selection operating in different portions of the life cycle.
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Affiliation(s)
- Allison B. Willis
- Department of Biological SciencesUniversity of South CarolinaColumbiaSouth CarolinaUSA
| | - Evgeniya Ermolaeva
- Department of Biological SciencesUniversity of South CarolinaColumbiaSouth CarolinaUSA
| | - Amaelia Zyck
- Department of Biological SciencesUniversity of South CarolinaColumbiaSouth CarolinaUSA
| | - Rhiannon Rognstad
- Department of Biological SciencesUniversity of South CarolinaColumbiaSouth CarolinaUSA
| | - Shannon Davis
- Department of Biological SciencesUniversity of South CarolinaColumbiaSouth CarolinaUSA
| | - Thomas J. Hilbish
- Department of Biological SciencesUniversity of South CarolinaColumbiaSouth CarolinaUSA
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2
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Diz AP, Skibinski DOF. Patterns of admixture and introgression in a mosaic Mytilus galloprovincialis and Mytilus edulis hybrid zone in SW England. Mol Ecol 2024; 33:e17233. [PMID: 38063472 DOI: 10.1111/mec.17233] [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: 07/20/2023] [Revised: 11/21/2023] [Accepted: 11/24/2023] [Indexed: 01/25/2024]
Abstract
The study of hybrid zones offers important insights into speciation. Earlier studies on hybrid populations of the marine mussel species Mytilus edulis and Mytilus galloprovincialis in SW England provided evidence of admixture but were constrained by the limited number of molecular markers available. We use 57 ancestry-informative SNPs, most of which have been mapped genetically, to provide evidence of distinctive differences between admixed populations in SW England and asymmetrical introgression from M. edulis to M. galloprovincialis. We combine the genetic study with analysis of phenotypic traits of potential ecological and adaptive significance. We demonstrate that hybrid individuals have brown mantle edges unlike the white or purple in the parental species, suggesting allelic or non-allelic genomic interactions. We report differences in gonad development stage between the species consistent with a prezygotic barrier between the species. By incorporating results from publications dating back to 1980, we confirm the long-term stability of the hybrid zone despite higher viability of M. galloprovincialis. This stability coincides with a dramatic change in temperature of UK coastal waters and suggests that these hybrid populations might be resisting the effects of global warming. However, a single SNP locus associated with the Notch transmembrane signalling protein shows a markedly different pattern of variation to the others and might be associated with adaptation of M. galloprovincialis to colder northern temperatures.
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Affiliation(s)
- Angel P Diz
- Centro de Investigación Mariña, Universidade de Vigo (CIM-UVIGO), Vigo, Spain
- Department of Biochemistry, Genetics and Immunology, University of Vigo, Vigo, Spain
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3
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Vendrami DLJ, De Noia M, Telesca L, Brodte E, Hoffman JI. Genome-wide insights into introgression and its consequences for genome-wide heterozygosity in the Mytilus species complex across Europe. Evol Appl 2020; 13:2130-2142. [PMID: 32908609 PMCID: PMC7463347 DOI: 10.1111/eva.12974] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2019] [Accepted: 03/24/2020] [Indexed: 11/26/2022] Open
Abstract
The three mussel species comprising the Mytilus complex are widespread across Europe and readily hybridize when they occur in sympatry, resulting in a mosaic of populations with varying genomic backgrounds. Two of these species, M. edulis and M. galloprovincialis, are extensively cultivated across Europe, with annual production exceeding 230,000 tonnes. The third species, M. trossulus, is considered commercially damaging as hybridization with this species results in weaker shells and poor meat quality. We therefore used restriction site associated DNA sequencing to generate high-resolution insights into the structure of the Mytilus complex across Europe and to resolve patterns of introgression. Inferred species distributions were concordant with the results of previous studies based on smaller numbers of genetic markers, with M. edulis and M. galloprovincialis predominating in northern and southern Europe respectively, while introgression between these species was most pronounced in northern France and the Shetland Islands. We also detected traces of M. trossulus ancestry in several northern European populations, especially around the Baltic and in northern Scotland. Finally, genome-wide heterozygosity, whether quantified at the population or individual level, was lowest in M. edulis, intermediate in M. galloprovincialis, and highest in M. trossulus, while introgression was positively associated with heterozygosity in M. edulis but negatively associated with heterozygosity in M. galloprovincialis. Our study will help to inform mussel aquaculture by providing baseline information on the genomic backgrounds of different Mytilus populations across Europe and by elucidating the effects of introgression on genome-wide heterozygosity, which is known to influence commercially important traits such as growth, viability, and fecundity in mussels.
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Affiliation(s)
| | - Michele De Noia
- Department of Animal BehaviorUniversity of BielefeldBielefeldGermany
- Institute of Biodiversity, Animal Health & Comparative MedicineCollege of Medical Veterinary & Life SciencesUniversity of GlasgowGlasgowUK
| | - Luca Telesca
- Department of Earth SciencesUniversity of CambridgeCambridgeUK
- British Antarctic Survey, High CrossCambridgeUK
| | | | - Joseph I. Hoffman
- Department of Animal BehaviorUniversity of BielefeldBielefeldGermany
- British Antarctic Survey, High CrossCambridgeUK
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4
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Rawson PD, Hilbish TJ. ASYMMETRIC INTROGRESSION OF MITOCHONDRIAL DNA AMONG EUROPEAN POPULATIONS OF BLUE MUSSELS (
MYTILUS
SPP.). Evolution 2017; 52:100-108. [DOI: 10.1111/j.1558-5646.1998.tb05142.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/1996] [Accepted: 07/02/1997] [Indexed: 11/30/2022]
Affiliation(s)
- Paul D. Rawson
- Department of Biological Sciences University of South Carolina Columbia South Carolina 29208
| | - Thomas J. Hilbish
- Department of Biological Sciences University of South Carolina Columbia South Carolina 29208
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5
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Oyarzún PA, Toro JE, Cañete JI, Gardner JP. Bioinvasion threatens the genetic integrity of native diversity and a natural hybrid zone: smooth-shelled blue mussels (Mytilusspp.) in the Strait of Magellan. Biol J Linn Soc Lond 2015. [DOI: 10.1111/bij.12687] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Affiliation(s)
- Pablo A. Oyarzún
- Instituto de Ciencias Marinas y Limnológicas (ICML); Facultad de Ciencias Universidad Austral de Chile; Independencia 641 Valdivia Chile
- PhD program in Marine Biology; Universidad Austral de Chile; Valdivia (UACH) Chile
| | - Jorge E. Toro
- Instituto de Ciencias Marinas y Limnológicas (ICML); Facultad de Ciencias Universidad Austral de Chile; Independencia 641 Valdivia Chile
| | - Juan I. Cañete
- Facultad de Ciencias; Universidad de Magallanes; Punta Arenas Chile
| | - Jonathan P.A. Gardner
- Centre for Marine Environmental and Economic Research; Victoria University of Wellington; P O Box 600 Wellington 6140 New Zealand
- Key Laboratory of Freshwater Animal Breeding; Ministry of Agriculture; College of Fisheries; Huazhong Agricultural University; Wuhan 430070 China
- Freshwater Aquaculture Collaborative Innovation Centre of Hubei Province; Wuhan 430070 China
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Roux C, Fraïsse C, Castric V, Vekemans X, Pogson GH, Bierne N. Can we continue to neglect genomic variation in introgression rates when inferring the history of speciation? A case study in a Mytilus hybrid zone. J Evol Biol 2014; 27:1662-75. [PMID: 24913446 DOI: 10.1111/jeb.12425] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2014] [Revised: 04/25/2014] [Accepted: 04/25/2014] [Indexed: 11/28/2022]
Abstract
The use of molecular data to reconstruct the history of divergence and gene flow between populations of closely related taxa represents a challenging problem. It has been proposed that the long-standing debate about the geography of speciation can be resolved by comparing the likelihoods of a model of isolation with migration and a model of secondary contact. However, data are commonly only fit to a model of isolation with migration and rarely tested against the secondary contact alternative. Furthermore, most demographic inference methods have neglected variation in introgression rates and assume that the gene flow parameter (Nm) is similar among loci. Here, we show that neglecting this source of variation can give misleading results. We analysed DNA sequences sampled from populations of the marine mussels, Mytilus edulis and M. galloprovincialis, across a well-studied mosaic hybrid zone in Europe and evaluated various scenarios of speciation, with or without variation in introgression rates, using an Approximate Bayesian Computation (ABC) approach. Models with heterogeneous gene flow across loci always outperformed models assuming equal migration rates irrespective of the history of gene flow being considered. By incorporating this heterogeneity, the best-supported scenario was a long period of allopatric isolation during the first three-quarters of the time since divergence followed by secondary contact and introgression during the last quarter. By contrast, constraining migration to be homogeneous failed to discriminate among any of the different models of gene flow tested. Our simulations thus provide statistical support for the secondary contact scenario in the European Mytilus hybrid zone that the standard coalescent approach failed to confirm. Our results demonstrate that genomic variation in introgression rates can have profound impacts on the biological conclusions drawn from inference methods and needs to be incorporated in future studies.
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Affiliation(s)
- C Roux
- Université Montpellier 2, Montpellier, France; CNRS-UMR5554 Institut des Sciences de l'Evolution, Station Méditerranéenne de l'Environnement Littoral, Sète, France; Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
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7
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GARDNER JONATHANPA, THOMPSON RAYMONDJ. Influence of genotype and geography on shell shape and morphometric trait variation among North Atlantic blue mussel (Mytilus spp.) populations. Biol J Linn Soc Lond 2009. [DOI: 10.1111/j.1095-8312.2008.01166.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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8
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SKIBINSKI DOF, RODERICK EE. Evidence of selective mortality in favour of the Mytilus galloprovincialis Lmk phenotype in British mussel populations. Biol J Linn Soc Lond 2008. [DOI: 10.1111/j.1095-8312.1991.tb00568.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Abstract
Hybrid zones are 'natural laboratories' for studying the origin, maintenance and demise of species. Theory predicts that hybrid zones can move in space and time, with significant consequences for both evolutionary and conservation biology, though such movement is often perceived as rare. Here, a review of empirical studies of moving hybrid zones in animals and plants shows 23 examples with observational evidence for movement, and a further 16 where patterns of introgression in molecular markers could be interpreted as signatures of movement. The strengths and weaknesses of methods used for detecting hybrid zone movement are discussed, including long-term replicated sampling, historical surveys, museum/herbarium collections, patterns of relictual populations and introgression of genetic markers into an advancing taxon. Factors governing hybrid zone movement are assessed in the light of the empirical studies, including environmental selection, competition, asymmetric hybridization, dominance drive, hybrid fitness, human activity and climate change. Hybrid zone movement means that untested assumptions of stability in evolutionary studies on hybrid zone can lead to mistaken conclusions. Movement also means that conservation effort aimed at protecting against introgression could unwittingly favour an invading taxon. Moving hybrid zones are of wide interest as examples of evolution in action and possible indicators of environmental change. More long-term experimental studies are needed that incorporate reciprocal transplants, hybridization experiments and surveys of molecular markers and population densities on a range of scales.
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10
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Abstract
Protein expression patterns were compared in mussels from a hybrid zone between the two species Mytilus edulis and M. galloprovincialis using 2-DE. Significant differences in expression pattern were observed between species and between mussels within species. Hybrid mussels had more variable protein expression patterns than mussels of each species. This could be due to segregation at expression modifier loci in the hybrids. It is proposed that unusual hybrid expression patterns might contribute to postzygotic isolation, if such patterns reduce fitness. The use of proteomic data for testing evolutionary models, as in many transcriptomics studies, is explored with results consistent with the expectations of neutral theory.
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Affiliation(s)
- Angel P Diz
- School of Medicine, University of Swansea, Singleton Park, Swansea, UK
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11
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Kartavtsev YP, Lee JS. Analysis of nucleotide diversity at the cytochrome b and cytochrome oxidase 1 genes at the population, species, and genus levels. RUSS J GENET+ 2006. [DOI: 10.1134/s1022795406040016] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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12
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Wood AR, Turner G, Skibinski DOF, Beaumont AR. Disruption of doubly uniparental inheritance of mitochondrial DNA in hybrid mussels (Mytilus edulis x M. galloprovincialis). Heredity (Edinb) 2004; 91:354-60. [PMID: 14512950 DOI: 10.1038/sj.hdy.6800345] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Blue mussels of the genus Mytilus have an unusual mode of mitochondrial DNA inheritance termed doubly uniparental inheritance (DUI). Females are homoplasmic for the F mitotype which is inherited maternally, whereas males are heteroplasmic for this and the paternally inherited M mitotype. In areas where species distributions overlap a varying degree of hybridization occurs; yet genetic differences between allopatric populations are maintained. Observations from natural populations and previous laboratory experiments suggest that DUI may be disrupted by hybridization, giving rise to heteroplasmic females and homoplasmic males. We carried out controlled laboratory crosses between Mytilus edulis and M. galloprovincialis to produce pure species and hybrid larvae of known parentage. DNA markers were used to follow the fate of the F and M mitotypes through larval development. Disruption of the mechanism which determines whether the M mitotype is retained or eliminated occurred in an estimated 38% of M. edulis x M. galloprovincialis hybrid larvae, a level double that previously observed in adult mussels from a natural M. edulis x M. galloprovincialis hybrid population. Furthermore, reciprocal hybrid crosses exhibited contrasting types of DUI disruption. The results indicate that disruption of DUI in hybrid mussels may be associated with increased mortality and hence could be a factor in the maintenance of genetic integrity for each species.
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Affiliation(s)
- A R Wood
- School of Ocean Sciences, University of Wales Bangor, Menai Bridge, Anglesey, Wales LL59 5EY, UK.
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13
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Abstract
Marine organisms challenge the classical theories of local adaptation and speciation because their planktonic larvae have the potential to maintain high gene flow. The marine-speciation paradox is illustrated by contact zones between incipient species that are so large that allopatric divergence seems unlikely. For this reason any mechanism preventing sympatric larvae of two incipient species from coexisting in the same habitats can be a powerful promoter of speciation. The contact zone between two hybridizing taxa of mussel, Mytilus edulis and M. galloprovincialis, in Europe provides an excellent example. Although the zone itself extends over thousands of kilometres, the opportunities for interbreeding are considerably reduced by the small-scale mosaic structure of the zone, where local patches of each taxon alternate at scales of kilometres or less, in response to locally variable ecological factors. Habitat choice by settling larvae would be a less costly mechanism than post-settlement selection to maintain such a mosaic structure. Unfortunately the role of selective settlement has remained hypothetical because larvae could not be scored by classical genetic markers. PCR markers allowed us to study larvae and settlement in ecologically contrasting sites within the zone. We show that only a subset of the genotypes present in the plankton settle in some sites, and that the adults on these sites show the same genetic bias. Genetically based variation in pre-settlement processes therefore accounts for the ecological segregation observed, though it is not the only factor involved in limiting successful interbreeding. The present dataset also supports previous reports of partial spawning asynchrony.
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Affiliation(s)
- Nicolas Bierne
- Laboratoire Génome, Populations, Interactions, Adaptation, Université Montpellier II-IFREMER-CNRS, UMR5000, SMEL, 34200 Sète, France.
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14
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Gilg MR, Hilbish TJ. Patterns of larval dispersal and their effect on the maintenance of a blue mussel hybrid zone in southwestern England. Evolution 2003; 57:1061-77. [PMID: 12836823 DOI: 10.1111/j.0014-3820.2003.tb00316.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The blue mussels Mytilus edulis and M. galloprovincialis hybridize in southwestern England. Within this hybrid zone environmentally based directional selection favors individuals with alleles specific to M. galloprovincialis. What forces are countering this directional selection and allowing for the maintenance of a stable hybrid population are unknown. We used both the genetics of recently settled larvae and a fine-scale model of the physical oceanography of the region to determine the patterns of larval dispersal throughout the hybrid zone and the bordering parental populations. Evidence from both the model and the genetics suggests that the hybrid zone lies between two barriers to dispersal. Start Point separates the M. edulis population from the hybrid zone and allows minimal dispersal from the hybrid zone into the M. edulis population, but none in the other direction. Likewise, the M. galloprovincialis populations along the northern coast of Cornwall regularly receive immigrating larvae from the hybrid zone, but larvae from the M. galloprovincialis population do not enter the hybrid zone. However, larvae settling at hybrid zone sites have high frequencies of alleles specific to M. edulis, suggesting that reproductive barriers, selection in the larval stage, or gene flow from an undetermined source is effectively balancing the directional selection observed in the adults.
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Affiliation(s)
- Matthew R Gilg
- Department of Biological Sciences, University of South Carolina, Columbia, South Carolina 29208, USA.
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15
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Bierne N, Borsa P, Daguin C, Jollivet D, Viard F, Bonhomme F, David P. Introgression patterns in the mosaic hybrid zone between Mytilus edulis and M. galloprovincialis. Mol Ecol 2003; 12:447-61. [PMID: 12535095 DOI: 10.1046/j.1365-294x.2003.01730.x] [Citation(s) in RCA: 143] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Hybrid zones are fascinating systems to investigate the structure of genetic barriers. Marine hybrid zones deserve more investigation because of the generally high dispersion potential of planktonic larvae which allows migration on scales unrivalled by terrestrial species. Here we analyse the genetic structure of the mosaic hybrid zone between the marine mussels Mytilus edulis and M. galloprovincialis, using three length-polymorphic PCR loci as neutral and diagnostic markers on 32 samples along the Atlantic coast of Europe. Instead of a single genetic gradient from M. galloprovincialis on the Iberian Peninsula to M. edulis populations in the North Sea, three successive transitions were observed in France. From South to North, the frequency of alleles typical of M. galloprovincialis first decreases in the southern Bay of Biscay, remains low in Charente, then increases in South Brittany, remains high in most of Brittany, and finally decreases again in South Normandy. The two enclosed patches observed in the midst of the mosaic hybrid zone in Charente and Brittany, although predominantly M. edulis-like and M. galloprovincialis-like, respectively, are genetically original in two respects. First, considering only the various alleles typical of one species, the patches show differentiated frequencies compared to the reference external populations. Second, each patch is partly introgressed by alleles of the other species. When introgression is taken into account, linkage disequilibria appear close to their maximum possible values, indicating a strong genetic barrier within all transition zones. Some pre- or postzygotic isolation mechanisms (habitat specialization, spawning asynchrony, assortative fertilization and hybrid depression) have been documented in previous studies, although their relative importance remains to be evaluated. We also provided evidence for a recent migratory 'short-cut' connecting M. edulis-like populations of the Charente patch to an external M. edulis population in Normandy and thought to reflect artificial transfer of spat for aquaculture.
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Affiliation(s)
- N Bierne
- Laboratoire Génome, Populations, Interactions, CNRS-UMR5000 - Station Méditerranéenne de l'Environnement Littoral, 1 Quai de la Daurade, 34200 Sète, France.
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16
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Gilg MR, Hilbish TJ. PATTERNS OF LARVAL DISPERSAL AND THEIR EFFECT ON THE MAINTENANCE OF A BLUE MUSSEL HYBRID ZONE IN SOUTHWESTERN ENGLAND. Evolution 2003. [DOI: 10.1554/0014-3820(2003)057[1061:poldat]2.0.co;2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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17
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Bierne N, David P, Boudry P, Bonhomme F. Assortative fertilization and selection at larval stage in the mussels Mytilus edulis and M. galloprovincialis. Evolution 2002; 56:292-8. [PMID: 11926497 DOI: 10.1111/j.0014-3820.2002.tb01339.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Assortative mating (prezygotic isolation) and reduced hybrid fitness (postzygotic isolation) are typically invoked to explain the stability of hybrid zones. In the tension zone model, these factors work in opposition to migration, which promotes genetic homogeneity. Many marine animals migrate over long distances through a planktonic larval stage. Therefore, strong reproductive isolation is needed to maintain stable marine hybrid zones. However, surprisingly little is known about mating preferences and hybrid fitness in marine organisms. Smooth-shelled mussels (Mytilus spp.) form a well-known species complex, with hybridization over extensive areas such as the contact zone of M. edulis and M. galloprovincialis around European Atlantic coasts. This paper reports direct experimental evidence of assortative fertilization, hybrid larval inviability, and early heterosis for growth rate in M. edulis and M. galloprovincialis. Four crosses between pure M. edulis and M. galloprovincialis were analyzed with a new polymerase-chain-reaction-based diagnostic marker. Gamete competition between taxa was allowed in two out of the four crosses. Genotype frequencies observed at an early stage (36 h after fertilization) unambiguously revealed assortative fertilization when gamete competition was allowed. A significant reduction in hybrid viability was subsequently observed during the larval stage. At the same stage an antagonistic effect, heterosis, was observed on growth rate. However, even if heterosis is observed in the F1, it is expected to vanish in subsequent hybrid generations. Although specialization for different habitats and asynchronous spawning have been mentioned as factors contributing to the maintenance of the blue mussel hybrid zone in Europe, we argue that assortative fertilization and reduced hybrid fitness are important factors that also contribute to the stabilization of this zone. These results emphasize that multiple factors may act concomitantly in a barrier to gene flow, especially in complex life cycles. Furthermore, they show that assortative mating through gamete preference, as already demonstrated for sea urchins, may play a role in speciation processes taking place in the sea.
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Affiliation(s)
- Nicolas Bierne
- Laboratoire Genome, Populations, Interactions, Centre National de la Recherche Scientifique-UMR5000, Station Méditerranéenne de l'Environment Littoral, Sète, France.
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18
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Bierne N, David P, Boudry P, Bonhomme F. ASSORTATIVE FERTILIZATION AND SELECTION AT LARVAL STAGE IN THE MUSSELS MYTILUS EDULIS AND M. GALLOPROVINCIALIS. Evolution 2002. [DOI: 10.1554/0014-3820(2002)056[0292:afasal]2.0.co;2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Daguin C, Bonhomme F, Borsa P. The zone of sympatry and hybridization of Mytilus edulis and M. galloprovincialis, as described by intron length polymorphism at locus mac-1. Heredity (Edinb) 2001; 86:342-54. [PMID: 11488971 DOI: 10.1046/j.1365-2540.2001.00832.x] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Intron-size variation at the actin gene locus mac-1 was used to characterize mussel, Mytilus spp., populations in the approximately 2000-km wide zone of contact and hybridization ('hybrid zone') between M. edulis and M. galloprovincialis in western Europe. Twenty-five samples were collected in 1995-99 in locations within the hybrid zone and from reference populations of each species. We used correspondence analysis on the matrix of allelic frequencies to determine which alleles are characteristic of each species, and to characterize samples along the genetic gradient between M. edulis and M. galloprovincialis. In the hybrid zone, some samples exhibited mac-1 allele frequencies that were typical of M. edulis; other samples were distributed along the M. edulis/M. galloprovincialis gradient and displayed variable levels of intergradation that were not correlated with geography. Some of the latter samples exhibited significant heterozygote deficiencies. The simple admixture hypothesis (Wahlund effect) could not be rejected for two-fifths of the samples. The hybrid zone thus appeared as a mosaic of populations which are either pure M. edulis, or hybrid between M. galloprovincialis and M. edulis, or a mixture of the foregoing with M. galloprovincialis individuals. These results were consistent with published allozyme data, suggesting that they can be extended to the entire nuclear genome. M. edulis mac-1 alleles were present at moderate frequency in Atlantic M. galloprovincialis, and at significantly lower frequency in some Mediterranean samples. This pattern was homogeneous over a broad geographical range within each basin. It was not evident that introgression of M. edulis into M. galloprovincialis presently occurs south of the zone of contact. We propose that the distinctness of the Atlantic M. galloprovincialis population results from past introgression by M. edulis alleles.
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Affiliation(s)
- C Daguin
- Laboratoire Génome Populations Interactions and IRD, UMR 5000 CNRS, Station Méditerranéenne de l'Environnement Littoral, 1 Quai de la Daurade, 34200 Sète, France
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Microgeographic allozyme differentiation in the hybrid zone ofMytilus galloprovincialis Lmk. andM. edulis L. on the continental European coast. ACTA ACUST UNITED AC 1997. [DOI: 10.1007/bf02908758] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Rawson PD, Joyner KL, Meetze K, Hilbish TJ. Evidence for intragenic recombination within a novel genetic marker that distinguishes mussels in the Mytilus edulis species complex. Heredity (Edinb) 1996; 77 ( Pt 6):599-607. [PMID: 8972080 DOI: 10.1038/hdy.1996.187] [Citation(s) in RCA: 96] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
We have used the polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) techniques to design two genetic markers for blue mussels in the Mytilus edulis species complex. Both of these markers target the gene encoding the mussel polyphenolic adhesive protein. The first marker, Glu-5', is highly differentiated among and can be used to identify the three blue mussel species, M. edulis, M. galloprovincialis and M. trossulus. The second marker, Glu-3', can identify M. edulis and M. galloprovincialis. Using these markers we have demonstrated that hybrid mussels from Whitsand Bay, UK carry alleles for this gene that are the products of intragenic recombination. The high frequency (10 per cent) of these recombinant alleles within the hybrid population suggests that recombination is fairly frequent within this gene or that hybridization between M. edulis and M. galloprovincialis is substantial and has been occurring over considerable evolutionary time. The two novel genetic markers, Glu-5' and Glu-3' will be invaluable in additional studies regarding the importance of hybridization among blue mussels.
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Affiliation(s)
- P D Rawson
- Department of Biological Sciences, University of South Carolina, Columbia 29201, USA
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HEATH DD, HATCHER DR, HILBISH TJ. Ecological interaction between sympatricMytilusspecies on the west coast of Canada investigated using PCR markers. Mol Ecol 1996. [DOI: 10.1046/j.1365-294x.1996.00087.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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HEATH DD, HATCHER DR, HILBISH TJ. Ecological interaction between sympatric Mytilus species on the west coast of Canada investigated using PCR markers. Mol Ecol 1996. [DOI: 10.1111/j.1365-294x.1996.tb00334.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Gardner J. The Mytilus edulis species complex in Southwest England: Multi-locus heterozygosity, background genotype and a fitness correlate. BIOCHEM SYST ECOL 1994. [DOI: 10.1016/0305-1978(94)90109-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Scarpa J, Allen SK. Comparative kinetics of meiosis in hybrid crosses of Pacific oysterCrassostrea gigas and Suminoe oysterC. rivularis with the American oysterC. virginica. ACTA ACUST UNITED AC 1992. [DOI: 10.1002/jez.1402630311] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Gardner JPA. Mytilus Galloprovincialis(Lmk) (Bivalvia, Mollusca): The Taxonomic Status of the Mediterranean Mussel. ACTA ACUST UNITED AC 1992. [DOI: 10.1080/00785326.1992.10429929] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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Coustau C, Renaud F, Maillard C, Pasteur N, Delay B. Differential susceptibility to a trematode parasite among genotypes of the Mytilus edulis/galloprovincialis complex. Genet Res (Camb) 1991; 57:207-12. [PMID: 1889741 DOI: 10.1017/s0016672300029359] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
We show that parasitism by the trematode Prosorhynchus squamatus in parental and introgressed Mytilus edulis/galloprovincialis (Bivalvia) mussels occurs in individuals with a predominantly M. edulis genome. This result suggests that the restricted specificity of P. squamatus is dependent on genetic factor(s) present in M. edulis. Because of its strong pathogenic effects (i.e. total castration and possible death), this parasite may be a source of intense selection against M. edulis genomes when they are present in a site. As a consequence, it may favour the geographic extension of the M. galloprovincialis genome. Previous studies have indicated that, in hybrid zones, recombinant genotypes are more susceptible to parasitic infections than either parental genotype. We demonstrate that this is not the case for the M. edulis/M. galloprovincialis system, and that the parental genotype alone determines susceptibility.
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Affiliation(s)
- C Coustau
- Laboratoire de Parasitologie Comparée (URA 698, CNRS), Université de Montpellier II, France
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