101
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Whittaker DJ, Dapper AL, Peterson MP, Atwell JW, Ketterson ED. Maintenance of MHC Class IIB diversity in a recently established songbird population. JOURNAL OF AVIAN BIOLOGY 2012; 43:109-118. [PMID: 22685370 PMCID: PMC3368239 DOI: 10.1111/j.1600-048x.2012.05504.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We examined variation at MHC Class IIB genes in a recently established population of dark-eyed juncos (Junco hyemalis) in a coastal urban environment in southern California, USA relative to an ancestral-range population from a nearby species-typical montane environment. The founding population is estimated to have been quite small, but we predicted that variation at the major histocompatibility complex (MHC) among the founders would nevertheless be preserved owing to the high functional significance of MHC. Previous studies of MHC in songbirds have had varying degrees of success in isolating loci, as passerines show extensive MHC gene duplication. In order to compare diversity in the two populations, we employed two published approaches to sequencing MHC Class II exon 2: direct sequencing with exon-based primers, and traditional cloning and sequencing with intron-based primers. Results from both methods show that the colonist population has maintained high levels of variation. Our results also indicate varying numbers of alleles across individuals, corroborating evidence for gene duplication in songbird MHC. While future studies in songbirds may need to take a genomic approach to fully understand the structure of MHC in this lineage, our results show that it is possible to use traditional methods to reveal functional variation across populations.
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Affiliation(s)
- Danielle J. Whittaker
- BEACON Center for the Study of Evolution in Action, Michigan State University, 1441 Biomedical and Physical Sciences, East Lansing, MI, 48824
- Department of Biology, Indiana University, 1001 East Third St, Bloomington, IN, 47405
| | - Amy L. Dapper
- Department of Biology, Indiana University, 1001 East Third St, Bloomington, IN, 47405
| | - Mark P. Peterson
- Department of Biology, Indiana University, 1001 East Third St, Bloomington, IN, 47405
| | - Jonathan W. Atwell
- Department of Biology, Indiana University, 1001 East Third St, Bloomington, IN, 47405
| | - Ellen D. Ketterson
- Department of Biology, Indiana University, 1001 East Third St, Bloomington, IN, 47405
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102
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MALÉ PIERREJEANG, MARTIN JEANFRANÇOIS, GALAN MAXIME, DEFFONTAINE VALÉRIE, BRYJA JOSEF, COSSON JEANFRANÇOIS, MICHAUX JOHAN, CHARBONNEL NATHALIE. Discongruence of Mhc and cytochrome b phylogeographical patterns in Myodes glareolus (Rodentia: Cricetidae). Biol J Linn Soc Lond 2012. [DOI: 10.1111/j.1095-8312.2011.01799.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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103
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Parasite-stress promotes in-group assortative sociality: the cases of strong family ties and heightened religiosity. Behav Brain Sci 2012; 35:61-79. [PMID: 22289223 DOI: 10.1017/s0140525x11000021] [Citation(s) in RCA: 227] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Throughout the world people differ in the magnitude with which they value strong family ties or heightened religiosity. We propose that this cross-cultural variation is a result of a contingent psychological adaptation that facilitates in-group assortative sociality in the face of high levels of parasite-stress while devaluing in-group assortative sociality in areas with low levels of parasite-stress. This is because in-group assortative sociality is more important for the avoidance of infection from novel parasites and for the management of infection in regions with high levels of parasite-stress compared with regions of low infectious disease stress. We examined this hypothesis by testing the predictions that there would be a positive association between parasite-stress and strength of family ties or religiosity. We conducted this study by comparing among nations and among states in the United States of America. We found for both the international and the interstate analyses that in-group assortative sociality was positively associated with parasite-stress. This was true when controlling for potentially confounding factors such as human freedom and economic development. The findings support the parasite-stress theory of sociality, that is, the proposal that parasite-stress is central to the evolution of social life in humans and other animals.
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104
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Barribeau SM, Villinger J, Waldman B. Ecological immunogenetics of life-history traits in a model amphibian. Biol Lett 2011; 8:405-7. [PMID: 22114322 PMCID: PMC3367720 DOI: 10.1098/rsbl.2011.0845] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Major histocompatibility complex (MHC) genes determine immune repertoires and social preferences of vertebrates. Immunological regulation of microbial assemblages associated with individuals influences their sociality, and should also affect their life-history traits. We exposed Xenopus laevis tadpoles to water conditioned by adult conspecifics. Then, we analysed tadpole growth, development and survivorship as a function of MHC class I and class II peptide-binding region amino acid sequence similarities between tadpoles and frogs that conditioned the water to which they were exposed. Tadpoles approached metamorphosis earlier and suffered greater mortality when exposed to immunogenetically dissimilar frogs. The results suggest that developmental regulatory cues, microbial assemblages or both are specific to MHC genotypes. Tadpoles may associate with conspecifics with which they share microbiota to which their genotypes are well adapted.
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Affiliation(s)
- Seth M Barribeau
- Experimental Ecology, Institute of Integrative Biology, ETH Zürich, Zürich 8092, Switzerland
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105
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Schunter C, Carreras-Carbonell J, Macpherson E, Tintoré J, Vidal-Vijande E, Pascual A, Guidetti P, Pascual M. Matching genetics with oceanography: directional gene flow in a Mediterranean fish species. Mol Ecol 2011; 20:5167-81. [PMID: 22097887 DOI: 10.1111/j.1365-294x.2011.05355.x] [Citation(s) in RCA: 107] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Genetic connectivity and geographic fragmentation are two opposing mechanisms determining the population structure of species. While the first homogenizes the genetic background across populations the second one allows their differentiation. Therefore, knowledge of processes affecting dispersal of marine organisms is crucial to understand their genetic distribution patterns and for the effective management of their populations. In this study, we use genetic analyses of eleven microsatellites in combination with oceanographic satellite and dispersal simulation data to determine distribution patterns for Serranus cabrilla, a ubiquitous demersal broadcast spawner, in the Mediterranean Sea. Pairwise population F(ST) values ranged between -0.003 and 0.135. Two genetically distinct clusters were identified, with a clear division located between the oceanographic discontinuities at the Ibiza Channel (IC) and the Almeria-Oran Front (AOF), revealing an admixed population in between. The Balearic Front (BF) also appeared to dictate population structure. Directional gene flow on the Spanish coast was observed as S. cabrilla dispersed from west to east over the AOF, from north to south on the IC and from south of the IC towards the Balearic Islands. Correlations between genetic and oceanographic data were highly significant. Seasonal changes in current patterns and the relationship between ocean circulation patterns and spawning season may also play an important role in population structure around oceanographic fronts.
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Affiliation(s)
- C Schunter
- Centre d'Estudis Avançats de Blanes-CSIC, Car Acc Cala St Francesc 14, Blanes, 17300 Girona, Spain
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106
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The last two millennias echo-catastrophes are the driving forces for the potential genetic advantage mechanisms in celiac disease. Med Hypotheses 2011; 77:773-6. [DOI: 10.1016/j.mehy.2011.07.034] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2011] [Accepted: 07/17/2011] [Indexed: 11/23/2022]
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107
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Tschirren B, Andersson M, Scherman K, Westerdahl H, Råberg L. Contrasting patterns of diversity and population differentiation at the innate immunity gene toll-like receptor 2 (TLR2) in two sympatric rodent species. Evolution 2011; 66:720-731. [PMID: 22380435 DOI: 10.1111/j.1558-5646.2011.01473.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Comparing patterns of diversity and divergence between populations at immune genes and neutral markers can give insights into the nature and geographic scale of parasite-mediated selection. To date, studies investigating such patterns of selection in vertebrates have primarily focused on the acquired branch of the immune system, whereas it remains largely unknown how parasite-mediated selection shapes innate immune genes both within and across vertebrate populations. Here, we present a study on the diversity and population differentiation at the innate immune gene Toll-like receptor 2 (TLR2) across nine populations of yellow-necked mice (Apodemus flavicollis) and bank voles (Myodes glareolus) in southern Sweden. In yellow-necked mice, TLR2 diversity was very low, as was TLR2 population differentiation compared to neutral loci. In contrast, several TLR2 haplotypes co-occurred at intermediate frequencies within and across bank vole populations, and pronounced isolation by distance between populations was observed. The diversity and differentiation at neutral loci was similar in the two species. These results indicate that parasite-mediated selection has been acting in dramatically different ways on a given immune gene in ecologically similar and sympatric species. Furthermore, the finding of TLR2 population differentiation at a small geographical scale in bank voles highlights that vertebrate innate immune defense may be evolutionarily more dynamic than has previously been appreciated.
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Affiliation(s)
- Barbara Tschirren
- Molecular Ecology and Evolution Lab, Department of Biology, Lund University, Sölvegatan 37, SE-223 62 Lund, SwedenInstitute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland E-mail:
| | - Martin Andersson
- Molecular Ecology and Evolution Lab, Department of Biology, Lund University, Sölvegatan 37, SE-223 62 Lund, SwedenInstitute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland E-mail:
| | - Kristin Scherman
- Molecular Ecology and Evolution Lab, Department of Biology, Lund University, Sölvegatan 37, SE-223 62 Lund, SwedenInstitute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland E-mail:
| | - Helena Westerdahl
- Molecular Ecology and Evolution Lab, Department of Biology, Lund University, Sölvegatan 37, SE-223 62 Lund, SwedenInstitute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland E-mail:
| | - Lars Råberg
- Molecular Ecology and Evolution Lab, Department of Biology, Lund University, Sölvegatan 37, SE-223 62 Lund, SwedenInstitute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland E-mail:
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108
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Bollmer JL, Ruder EA, Johnson JA, Eimes JA, Dunn PO. Drift and selection influence geographic variation at immune loci of prairie-chickens. Mol Ecol 2011; 20:4695-706. [PMID: 22008237 DOI: 10.1111/j.1365-294x.2011.05319.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Previous studies of immunity in wild populations have focused primarily on genes of the major histocompatibility complex (MHC); however, studies of model species have identified additional immune-related genes that also affect fitness. In this study, we sequenced five non-MHC immune genes in six greater prairie-chicken (Tympanuchus cupido) populations that have experienced varying degrees of genetic drift as a consequence of population bottlenecks and fragmentation. We compared patterns of geographic variation at the immune genes with six neutral microsatellite markers to investigate the relative effects of selection and genetic drift. Global F(ST) outlier tests identified positive selection on just one of five immune genes (IAP-1) in one population. In contrast, at other immune genes, standardized G'(ST) values were lower than those at microsatellites for a majority of pairwise population comparisons, consistent with balancing selection or with species-wide positive or purifying selection resulting in similar haplotype frequencies across populations. The effects of genetic drift were also evident as summary statistics (e.g., Tajima's D) did not differ from neutrality for the majority of cases, and immune gene diversity (number of haplotypes per gene) was correlated positively with population size. In summary, we found that both genetic drift and selection shaped variation at the five immune genes, and the strength and type of selection varied among genes. Our results caution that neutral forces, such as drift, can make it difficult to detect current selection on genes.
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Affiliation(s)
- Jennifer L Bollmer
- Department of Biological Sciences, University of Wisconsin-Milwaukee, P.O. Box 413, Milwaukee, WI 53201, USA.
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109
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MacManes MD. Promiscuity in mice is associated with increased vaginal bacterial diversity. Naturwissenschaften 2011; 98:951-60. [PMID: 21964973 DOI: 10.1007/s00114-011-0848-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2011] [Revised: 09/11/2011] [Accepted: 09/12/2011] [Indexed: 12/15/2022]
Abstract
Differences in the number of sexual partners (i.e., mating system) have the potential to exert a strong influence on the bacterial communities present in reproductive structures like the vagina. Because this structure serves as a conduit for gametes, bacteria present there may have a pronounced, direct effect on host reproductive success. As a first step towards the identification of the relationship between sexual behavior and potentially pathogenic bacterial communities inhabiting vital reproductive structures, as well as their potential effects on fitness, I sought to quantify differences in bacterial diversity in a promiscuous and monogamous mammal species. To accomplish this, I used two sympatric species of Peromyscus rodents--Peromyscus californicus and Peromyscus maniculatus that differ with regard to the number of sexual partners per individual to test the hypothesis that bacterial diversity should be greater in the promiscuous P. maniculatus relative to the monogamous P. californicus. As predicted, phylogenetically controlled and operational taxonomic unit-based indices of bacterial diversity indicated that diversity is greater in the promiscuous species. These results provide important new insights into the effects of mating system on bacterial diversity in free-living vertebrates, and may suggest a potential cost of promiscuity.
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Affiliation(s)
- Matthew David MacManes
- Museum of Vertebrate Zoology and Department of Integrative Biology, University of California, Berkeley, 3101 Valley Life Sciences Building, Berkeley, CA 94720, USA.
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110
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Bordes F, Morand S. The impact of multiple infections on wild animal hosts: a review. Infect Ecol Epidemiol 2011; 1:IEE-1-7346. [PMID: 22957114 PMCID: PMC3426331 DOI: 10.3402/iee.v1i0.7346] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2011] [Revised: 08/11/2011] [Accepted: 08/25/2011] [Indexed: 12/23/2022] Open
Abstract
Field parasitological studies consistently demonstrate the reality of polyparasitism in natural systems. However, only recently, studies from ecological and evolutionary fields have emphasised a broad spectrum of potential multiple infections-related impacts. The main goal of our review is to reunify the different approaches on the impacts of polyparasitism, not only from laboratory or human medical studies but also from field or theoretical studies. We put forward that ecological and epidemiological determinants to explain the level of polyparasitism, which regularly affects not only host body condition, survival or reproduction but also host metabolism, genetics or immune investment. Despite inherent limitations of all these studies, multiple infections should be considered more systematically in wildlife to better appreciate the importance of parasite diversity in wildlife, cumulative effects of parasitism on the ecology and evolution of their hosts.
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Affiliation(s)
- Frédéric Bordes
- Institut des Sciences de l'Evolution, CNRS-UM2, CC65, Université de Montpellier, Montpellier, France
| | - Serge Morand
- Institut des Sciences de l'Evolution, CNRS-UM2, CC65, Université de Montpellier, Montpellier, France
- UR22 AGIRs, CIRAD, Campus International de Baillarguet, 34398, Montpellier, France
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111
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Perrier C, Guyomard R, Bagliniere JL, Evanno G. Determinants of hierarchical genetic structure in Atlantic salmon populations: environmental factors vs. anthropogenic influences. Mol Ecol 2011; 20:4231-45. [PMID: 21917045 DOI: 10.1111/j.1365-294x.2011.05266.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Disentangling the effects of natural environmental features and anthropogenic factors on the genetic structure of endangered populations is an important challenge for conservation biology. Here, we investigated the combined influences of major environmental features and stocking with non-native fish on the genetic structure and local adaptation of Atlantic salmon (Salmo salar) populations. We used 17 microsatellite loci to genotype 975 individuals originating from 34 French rivers. Bayesian analyses revealed a hierarchical genetic structure into five geographically distinct clusters. Coastal distance, geological substrate and river length were strong predictors of population structure. Gene flow was higher among rivers with similar geologies, suggesting local adaptation to geological substrate. The effect of river length was mainly owing to one highly differentiated population that has the farthest spawning grounds off the river mouth (up to 900km) and the largest fish, suggesting local adaptation to river length. We detected high levels of admixture in stocked populations but also in neighbouring ones, implying large-scale impacts of stocking through dispersal of non-native individuals. However, we found relatively few admixed individuals suggesting a lower fitness of stocked fish and/or some reproductive isolation between wild and stocked individuals. When excluding stocked populations, genetic structure increased as did its correlation with environmental factors. This study overall indicates that geological substrate and river length are major environmental factors influencing gene flow and potential local adaptation among Atlantic salmon populations but that stocking with non-native individuals may ultimately disrupt these natural patterns of gene flow among locally adapted populations.
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Affiliation(s)
- Charles Perrier
- INRA, UMR 0985 Ecology and Health of Ecosystems, 35042 Rennes, France.
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112
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de Eyto E, McGinnity P, Huisman J, Coughlan J, Consuegra S, Farrell K, O'Toole C, Tufto J, Megens HJ, Jordan W, Cross T, Stet RJM. Varying disease-mediated selection at different life-history stages of Atlantic salmon in fresh water. Evol Appl 2011; 4:749-62. [PMID: 25568020 PMCID: PMC3352546 DOI: 10.1111/j.1752-4571.2011.00197.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2010] [Accepted: 06/10/2011] [Indexed: 02/03/2023] Open
Abstract
Laboratory studies on associations between disease resistance and susceptibility and major histocompatibility (MH) genes in Atlantic salmon Salmo salar have shown the importance of immunogenetics in understanding the capacity of populations to fight specific diseases. However, the occurrence and virulence of pathogens may vary spatially and temporally in the wild, making it more complicated to predict the overall effect that MH genes exert on fitness of natural populations and over several life-history stages. Here we show that MH variability is a significant determinant of salmon survival in fresh water, by comparing observed and expected genotype frequencies at MH and control microsatellite loci at parr and migrant stages in the wild. We found that additive allelic effects at immunogenetic loci were more likely to determine survival than dominance deviation, and that selection on certain MH alleles varied with life stage, possibly owing to varying pathogen prevalence and/or virulence over time. Our results highlight the importance of preserving genetic diversity (particularly at MH loci) in wild populations, so that they have the best chance of adapting to new and increased disease challenges as a result of projected climate warming and increasing aquaculture.
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Affiliation(s)
| | - Philip McGinnity
- Department of Zoology, Ecology and Plant Science/Aquaculture and Fisheries Development Centre, University College Cork Distillery Fields, North Mall, Cork, Ireland
| | - Jisca Huisman
- Department of Biology, Norwegian University of Science and Technology Trondheim, Norway
| | - Jamie Coughlan
- Department of Zoology, Ecology and Plant Science/Aquaculture and Fisheries Development Centre, University College Cork Distillery Fields, North Mall, Cork, Ireland
| | - Sofia Consuegra
- Aberystwyth University, Institute of Biological, Environmental & Rural Sciences Aberystwyth, UK
| | | | - Ciar O'Toole
- Department of Zoology, Ecology and Plant Science/Aquaculture and Fisheries Development Centre, University College Cork Distillery Fields, North Mall, Cork, Ireland
| | - Jarle Tufto
- Department of Mathematical Sciences, Norwegian University of Science and Technology Trondheim, Norway
| | - Hendrik-Jan Megens
- Department of Animal Sciences, Wageningen University Wageningen, the Netherlands
| | - William Jordan
- Institute of Zoology, Zoological Society of London Regent's Park, London, UK
| | - Tom Cross
- Department of Zoology, Ecology and Plant Science/Aquaculture and Fisheries Development Centre, University College Cork Distillery Fields, North Mall, Cork, Ireland
| | - Rene J M Stet
- Scottish Fish Immunology Research Centre, University of Aberdeen Zoology Building, Tillydrone Avenue, Aberdeen, UK
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113
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Freamo H, O'Reilly P, Berg PR, Lien S, Boulding EG. Outlier SNPs show more genetic structure between two Bay of Fundy metapopulations of Atlantic salmon than do neutral SNPs. Mol Ecol Resour 2011; 11 Suppl 1:254-67. [PMID: 21429179 DOI: 10.1111/j.1755-0998.2010.02952.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Atlantic salmon of Eastern Canada were once of considerable importance to aboriginal, recreational, and commercial fisheries, yet many populations are now in decline, particularly those of the inner Bay of Fundy (iBoF), which were recently listed as endangered. We investigated whether nonneutral SNPs could be used to assign individual Atlantic salmon accurately to either the iBoF or the outer Bay of Fundy (oBoF) metapopulations because this has been difficult with existing neutral markers. We first searched for markers under diversifying selection by genotyping eight captively bred Bay of Fundy (BoF) populations for 320 SNP loci with the Sequenom MassARRAY™ system and then analysed the data set with four different F(ST) outlier detection programs. Three outlier loci were identified by both BayesFST and BayeScan whereas seven outlier loci, including the three previously mentioned, were identified by both Fdist and Arlequin. A subset of 14 nonneutral SNPs was more accurate (85% accuracy) than a subset of 67 neutral SNPs (75% accuracy) at assigning individual salmon back to their metapopulation. We then chose a subset of nine outlier SNP markers and used them to inexpensively genotype archived DNA samples from seven wild BoF populations using Invader™ chemistry. Hierarchical AMOVA of these independent wild samples corroborated our previous findings of significant genetic differentiation between iBoF and oBoF salmon metapopulations. Our research shows that identifying and using outlier loci is an important step towards achieving the goal of consistently and accurately distinguishing iBoF from oBoF Atlantic salmon, which will aid in their conservation.
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Affiliation(s)
- Heather Freamo
- Department of Integrative Biology, University of Guelph, Ontario, Canada
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114
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Evans ML, Dionne M, Miller KM, Bernatchez L. Mate choice for major histocompatibility complex genetic divergence as a bet-hedging strategy in the Atlantic salmon (Salmo salar). Proc Biol Sci 2011; 279:379-86. [PMID: 21697172 DOI: 10.1098/rspb.2011.0909] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Major histocompatibility complex (MHC)-dependent mating preferences have been observed across vertebrate taxa and these preferences are expected to promote offspring disease resistance and ultimately, viability. However, little empirical evidence linking MHC-dependent mate choice and fitness is available, particularly in wild populations. Here, we explore the adaptive potential of previously observed patterns of MHC-dependent mate choice in a wild population of Atlantic salmon (Salmo salar) in Québec, Canada, by examining the relationship between MHC genetic variation and adult reproductive success and offspring survival over 3 years of study. While Atlantic salmon choose their mates in order to increase MHC diversity in offspring, adult reproductive success was in fact maximized between pairs exhibiting an intermediate level of MHC dissimilarity. Moreover, patterns of offspring survival between years 0+ and 1+, and 1+ and 2+ and population genetic structure at the MHC locus relative to microsatellite loci indicate that strong temporal variation in selection is likely to be operating on the MHC. We interpret MHC-dependent mate choice for diversity as a likely bet-hedging strategy that maximizes parental fitness in the face of temporally variable and unpredictable natural selection pressures.
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Affiliation(s)
- Melissa L Evans
- Institut de Biologie Intégrative et des Systèmes, Pavillon Charles-Eugène-Marchand, 1030 Avenue de la Médecine, Université Laval, Québec, Canada.
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115
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Moutou KA, Mamuris Z, Firme T, Kontou M, Sarafidou T, Stoumboudi MT. Patterns of variability at the major histocompatibility class I and class II loci in populations of the endangered cyprinid Ladigesocypris ghigii. CONSERV GENET 2011. [DOI: 10.1007/s10592-011-0217-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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116
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Agudo R, Alcaide M, Rico C, Lemus JA, Blanco G, Hiraldo F, Donázar JA. Major histocompatibility complex variation in insular populations of the Egyptian vulture: inferences about the roles of genetic drift and selection. Mol Ecol 2011; 20:2329-40. [PMID: 21535276 DOI: 10.1111/j.1365-294x.2011.05107.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Insular populations have attracted the attention of evolutionary biologists because of their morphological and ecological peculiarities with respect to their mainland counterparts. Founder effects and genetic drift are known to distribute neutral genetic variability in these demes. However, elucidating whether these evolutionary forces have also shaped adaptive variation is crucial to evaluate the real impact of reduced genetic variation in small populations. Genes of the major histocompatibility complex (MHC) are classical examples of evolutionarily relevant loci because of their well-known role in pathogen confrontation and clearance. In this study, we aim to disentangle the partial roles of genetic drift and natural selection in the spatial distribution of MHC variation in insular populations. To this end, we integrate the study of neutral (22 microsatellites and one mtDNA locus) and MHC class II variation in one mainland (Iberia) and two insular populations (Fuerteventura and Menorca) of the endangered Egyptian vulture (Neophron percnopterus). Overall, the distribution of the frequencies of individual MHC alleles (n=17 alleles from two class II B loci) does not significantly depart from neutral expectations, which indicates a prominent role for genetic drift over selection. However, our results point towards an interesting co-evolution of gene duplicates that maintains different pairs of divergent alleles in strong linkage disequilibrium on islands. We hypothesize that the co-evolution of genes may counteract the loss of genetic diversity in insular demes, maximize antigen recognition capabilities when gene diversity is reduced, and promote the co-segregation of the most efficient allele combinations to cope with local pathogen communities.
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Affiliation(s)
- Rosa Agudo
- Department of Conservation Biology, Doñana Biological Station-CSIC, Avenida Américo Vespucio s/n, E-41092 Sevilla, Spain.
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117
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Keller I, Taverna A, Seehausen O. Evidence of neutral and adaptive genetic divergence between European trout populations sampled along altitudinal gradients. Mol Ecol 2011; 20:1888-904. [PMID: 21418113 DOI: 10.1111/j.1365-294x.2011.05067.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Species with a wide geographical distribution are often composed of distinct subgroups which may be adapted to their local environment. European trout (Salmo trutta species complex) provide an example of such a complex consisting of several genetically and ecologically distinct forms. However, trout populations are strongly influenced by human activities, and it is unclear to what extent neutral and adaptive genetic differences have persisted. We sampled 30 Swiss trout populations from heterogeneous environments along replicated altitudinal gradients in three major European drainages. More than 850 individuals were genotyped at 18 microsatellite loci which included loci diagnostic for evolutionary lineages and candidate markers associated with temperature tolerance, reproductive timing and immune defence. We find that the phylogeographic structure of Swiss trout populations has not been completely erased by stocking. Distinct genetic clusters corresponding to the different drainages could be identified, although nonindigenous alleles were clearly present, especially in the two Mediterranean drainages. We also still detected neutral genetic differentiation within rivers which was often associated with the geographical distance between populations. Five loci showed evidence of divergent selection between populations with several drainage-specific patterns. Lineage-diagnostic markers, a marker linked to a quantitative trait locus for upper temperature tolerance in other salmonids and a marker linked to the major histocompatibility class I gene were implicated in local adaptation and some patterns were associated with altitude. In contrast, tentative evidence suggests a signal of balancing selection at a second immune relevant gene (TAP2). Our results confirm the persistence of both neutral and potentially adaptive genetic differences between trout populations in the face of massive human-mediated dispersal.
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Affiliation(s)
- I Keller
- Department of Fish Ecology and Evolution, EAWAG Swiss Federal Institute of Aquatic Science and Technology, Center of Ecology, Evolution and Biochemistry, Seestrasse 79, CH-6047 Kastanienbaum, Switzerland.
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Gomez-Uchida D, Seeb JE, Smith MJ, Habicht C, Quinn TP, Seeb LW. Single nucleotide polymorphisms unravel hierarchical divergence and signatures of selection among Alaskan sockeye salmon (Oncorhynchus nerka) populations. BMC Evol Biol 2011; 11:48. [PMID: 21332997 PMCID: PMC3049142 DOI: 10.1186/1471-2148-11-48] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2010] [Accepted: 02/18/2011] [Indexed: 01/17/2023] Open
Abstract
Background Disentangling the roles of geography and ecology driving population divergence and distinguishing adaptive from neutral evolution at the molecular level have been common goals among evolutionary and conservation biologists. Using single nucleotide polymorphism (SNP) multilocus genotypes for 31 sockeye salmon (Oncorhynchus nerka) populations from the Kvichak River, Alaska, we assessed the relative roles of geography (discrete boundaries or continuous distance) and ecology (spawning habitat and timing) driving genetic divergence in this species at varying spatial scales within the drainage. We also evaluated two outlier detection methods to characterize candidate SNPs responding to environmental selection, emphasizing which mechanism(s) may maintain the genetic variation of outlier loci. Results For the entire drainage, Mantel tests suggested a greater role of geographic distance on population divergence than differences in spawn timing when each variable was correlated with pairwise genetic distances. Clustering and hierarchical analyses of molecular variance indicated that the largest genetic differentiation occurred between populations from distinct lakes or subdrainages. Within one population-rich lake, however, Mantel tests suggested a greater role of spawn timing than geographic distance on population divergence when each variable was correlated with pairwise genetic distances. Variable spawn timing among populations was linked to specific spawning habitats as revealed by principal coordinate analyses. We additionally identified two outlier SNPs located in the major histocompatibility complex (MHC) class II that appeared robust to violations of demographic assumptions from an initial pool of eight candidates for selection. Conclusions First, our results suggest that geography and ecology have influenced genetic divergence between Alaskan sockeye salmon populations in a hierarchical manner depending on the spatial scale. Second, we found consistent evidence for diversifying selection in two loci located in the MHC class II by means of outlier detection methods; yet, alternative scenarios for the evolution of these loci were also evaluated. Both conclusions argue that historical contingency and contemporary adaptation have likely driven differentiation between Kvichak River sockeye salmon populations, as revealed by a suite of SNPs. Our findings highlight the need for conservation of complex population structure, because it provides resilience in the face of environmental change, both natural and anthropogenic.
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119
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Contrasting responses to selection in class I and class IIα major histocompatibility-linked markers in salmon. Heredity (Edinb) 2011; 107:143-54. [PMID: 21266985 DOI: 10.1038/hdy.2010.177] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Comparison of levels and patterns of genetic variation in natural populations either across loci or against neutral expectation can yield insight into locus-specific differences in the strength and direction of evolutionary forces. We used both approaches to test the hypotheses on patterns of selection on major histocompatibility (MH)-linked markers. We performed temporal analyses of class I and class IIα MH-linked markers and eight microsatellite loci in two Atlantic salmon populations in Ireland on two temporal scales: over six decades and 9 years in the rivers Burrishoole and Delphi, respectively. We also compared contemporary Burrishoole and Delphi samples with nearby populations for the same loci. On comparing patterns of temporal and spatial differentiation among classes of loci, the class IIα MH-linked marker was consistently identified as an outlier compared with patterns at the other microsatellite loci or neutral expectation. We found higher levels of temporal and spatial heterogeneity in heterozygosity (but not in allelic richness) for the class IIα MH-linked marker compared with microsatellites. Tests on both within- and among-population differentiation are consistent with directional selection acting on the class IIα-linked marker in both temporal and spatial comparisons, but only in temporal comparisons for the class I-linked marker. Our results indicate a complex pattern of selection on MH-linked markers in natural populations of Atlantic salmon. These findings highlight the importance of considering selection on MH-linked markers when using these markers for management and conservation purposes.
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120
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Fraser DJ, Weir LK, Bernatchez L, Hansen MM, Taylor EB. Extent and scale of local adaptation in salmonid fishes: review and meta-analysis. Heredity (Edinb) 2011; 106:404-20. [PMID: 21224881 DOI: 10.1038/hdy.2010.167] [Citation(s) in RCA: 239] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
What is the extent and scale of local adaptation (LA)? How quickly does LA arise? And what is its underlying molecular basis? Our review and meta-analysis on salmonid fishes estimates the frequency of LA to be ∼55-70%, with local populations having a 1.2 times average fitness advantage relative to foreign populations or to their performance in new environments. Salmonid LA is evident at a variety of spatial scales (for example, few km to>1000 km) and can manifest itself quickly (6-30 generations). As the geographic scale between populations increases, LA is generally more frequent and stronger. Yet the extent of LA in salmonids does not appear to differ from that in other assessed taxa. Moreover, the frequency with which foreign salmonid populations outperform local populations (∼23-35%) suggests that drift, gene flow and plasticity often limit or mediate LA. The relatively few studies based on candidate gene and genomewide analyses have identified footprints of selection at both small and large geographical scales, likely reflecting the specific functional properties of loci and the associated selection regimes (for example, local niche partitioning, pathogens, parasites, photoperiodicity and seasonal timing). The molecular basis of LA in salmonids is still largely unknown, but differential expression at the same few genes is implicated in the convergent evolution of certain phenotypes. Collectively, future research will benefit from an integration of classical and molecular approaches to understand: (i) species differences and how they originate, (ii) variation in adaptation across scales, life stages, population sizes and environmental gradients, and (iii) evolutionary responses to human activities.
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Affiliation(s)
- D J Fraser
- Department of Biology, Concordia University, Montreal, Québec, Canada.
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121
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McCairns RJS, Bourget S, Bernatchez L. Putative causes and consequences of MHC variation within and between locally adapted stickleback demes. Mol Ecol 2010; 20:486-502. [PMID: 21134013 DOI: 10.1111/j.1365-294x.2010.04950.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Genes of the major histocompatibility complex (MHC) have been a source of considerable research interest, owing in large part to the growing body of evidence that they may be subject to both natural and sexual selection. However, much remains to be learned about the dynamics of MHC genes in subdivided populations, particularly those characterized by divergent ecological pressures. In this study, we attempt to disentangle the relative roles of both parasite-mediated selection and MHC-mediated mate choice in an open estuarine system inhabited by two parapatric, adaptively divergent threespine stickleback (Gasterosteus aculeatus) demes. We sequenced the putative peptide-binding region (PBR) of an estimated four Class IIβ loci from 127 individuals, identifying 329 sequence variants (276 translated amino acid sequences). Demes differed significantly both in the frequency of MHC alleles and in the communities of helminth parasites infecting resident sticklebacks. Strong signatures of natural selection were inferred from analyses of codon substitutions, particularly in the derived (freshwater) rather than the ancestral (marine) deme. Relationships between parasite load and MHC diversity were indicative of balancing selection, but only within the freshwater deme. Signals of MHC-mediated mate choice were weak and differed significantly between demes. Moreover, MHC-mediated mate choice was significantly influenced by environmental salinity and appeared of secondary importance to tendencies towards assortative mating. We discuss the implications of these findings in respect to ecological adaptation and the potential demographic consequences of possible outcomes of MHC-mediated mate choice.
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122
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Jeukens J, Renaut S, St-Cyr J, Nolte AW, Bernatchez L. The transcriptomics of sympatric dwarf and normal lake whitefish (Coregonus clupeaformis spp., Salmonidae) divergence as revealed by next-generation sequencing. Mol Ecol 2010; 19:5389-403. [PMID: 21087448 DOI: 10.1111/j.1365-294x.2010.04934.x] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Gene expression divergence is one of the mechanisms thought to be involved in the emergence of incipient species. Next-generation sequencing has become an extremely valuable tool for the study of this process by allowing whole transcriptome sequencing, or RNA-Seq. We have conducted a 454 GS-FLX pyrosequencing experiment to refine our understanding of adaptive divergence between dwarf and normal lake whitefish species (Coregonus clupeaformis spp.). The objectives were to: (i) investigate transcriptomic divergence as measured by liver RNA-Seq; (ii) test the correlation between divergence in expression and sequence polymorphism; and (iii) investigate the extent of allelic imbalance. We also compared the results of RNA-seq with those of a previous microarray study performed on the same fish. Following de novo assembly, results showed that normal whitefish overexpressed more contigs associated with protein synthesis while dwarf fish overexpressed more contigs related to energy metabolism, immunity and DNA replication and repair. Moreover, 63 SNPs showed significant allelic imbalance, and this phenomenon prevailed in the recently diverged dwarf whitefish. Results also showed an absence of correlation between gene expression divergence as measured by RNA-Seq and either polymorphism rate or sequence divergence between normal and dwarf whitefish. This study reiterates an important role for gene expression divergence, and provides evidence for allele-specific expression divergence as well as evolutionary decoupling of regulatory and coding sequences in the adaptive divergence of normal and dwarf whitefish. It also demonstrates how next-generation sequencing can lead to a more comprehensive understanding of transcriptomic divergence in a young species pair.
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Affiliation(s)
- Julie Jeukens
- Institut de Biologie Intégrative et des Systèmes (IBIS), Québec-Océan, Université Laval, Québec, QC, Canada.
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123
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Narum SR, Campbell NR, Kozfkay CC, Meyer KA. Adaptation of redband trout in desert and montane environments. Mol Ecol 2010; 19:4622-37. [PMID: 20880387 DOI: 10.1111/j.1365-294x.2010.04839.x] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Natural populations that evolve under extreme climates are likely to diverge because of selection in local environments. To explore whether local adaptation has occurred in redband trout (Oncorhynchus mykiss gairdneri) occupying differing climate regimes, we used a limited genome scan approach to test for candidate markers under selection in populations occurring in desert and montane streams. An environmental approach to identifying outlier loci, spatial analysis method and linear regression of minor allele frequency with environmental variables revealed six candidate markers (P < 0.01). Putatively neutral markers identified high genetic differentiation among desert populations relative to montane sites, likely due to intermittent flows in desert streams. Additionally, populations exhibited a highly significant pattern of isolation by temperature (P< 0.0001) and those adapted to the same environment had similar allele frequencies across candidate markers, indicating selection for differing climates. These results imply that many genes are involved in the adaptation of redband trout to differing environments, and selection acts to reinforce localization. The potential to predict genetic adaptability of individuals and populations to changing environmental conditions may have profound implications for species that face extensive anthropogenic disturbances.
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Affiliation(s)
- Shawn R Narum
- Columbia River Inter-Tribal Fish Commission, Hagerman Fish Culture Experiment Station, 3059F National Fish Hatchery Road, Hagerman, ID 83332, USA.
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124
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Jia Z, Chi X, Li C, Shi L. Development of MHC class I and II B primers in common carp and its molecular characterization. Biochem Genet 2010; 48:690-5. [PMID: 20524055 DOI: 10.1007/s10528-010-9351-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2009] [Accepted: 03/02/2010] [Indexed: 11/30/2022]
Abstract
The major histocompatibility complex (MHC) has an important role in immune response and is known as the most polymorphic locus in vertebrates. We developed three pairs of polymerase chain reaction primers of the alpha-2 domain (exon 3) of MHC class I and the beta-2 (exon 3) and beta-3 domains (exon 4) of MHC class II B gene in the German mirror common carp (Cyprinus carpio L.). We analyzed the three loci in a population of 65 individuals that had suffered the serious disease of gill rot. Five to six variable nucleotide sites and two to six variable amino acid sites (71.43%) were detected in the exon sequence of the sampled populations, indicating that many of them corresponded to amino acids involved in antigen recognition. Deviation from Hardy-Weinberg equilibrium and linkage disequilibrium were differentially found in some loci, which will be important for further study of disease resistance/susceptibility and population evolution.
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Affiliation(s)
- Zhiying Jia
- Heilongjiang River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Harbin, China
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125
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Radwan J, Biedrzycka A, Babik W. Does reduced MHC diversity decrease viability of vertebrate populations? BIOLOGICAL CONSERVATION 2010; 143:537-544. [PMID: 32226082 PMCID: PMC7092871 DOI: 10.1016/j.biocon.2009.07.026] [Citation(s) in RCA: 167] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2009] [Revised: 07/09/2009] [Accepted: 07/27/2009] [Indexed: 05/12/2023]
Abstract
Loss of genetic variation may render populations more vulnerable to pathogens due to inbreeding depression and depletion of variation in genes responsible for immunity against parasites. Here we review the evidence for the significance of variation in genes of the Major Histocompatibility Complex (MHC) for conservation efforts. MHC molecules present pathogen-derived antigens to the effector cells of the immune system and thus trigger the adaptive immune response. Some MHC genes are the most variable functional genes in the vertebrate genome. Their variation is clearly of adaptive significance and there is considerable evidence that its maintenance is mainly due to balancing selection imposed by pathogens. However, while the evidence for selection shaping MHC variation on the historical timescale is compelling, a correlation between levels of MHC variation and variation at neutral loci is often observed, indicating that on a shorter timescale drift also substantially affects MHC, leading to depletion of MHC diversity. The evidence that the loss of MHC variation negatively affects population survival is so far equivocal and difficult to separate from effects of general inbreeding. Some species with depleted MHC variation seem to be particularly susceptible to infection, but other species thrive and expand following severe bottlenecks that have drastically limited their MHC variation. However, while the latter demonstrate that MHC variation is not always critical for population survival, these species may in fact represent rare examples of survival despite of the loss of MHC variation. There is clearly a compelling need for data that would disclose the possible consequences of MHC diversity for population viability. In particular, we need more data on the impact of MHC allelic richness on the abundance of parasites or prevalence of disease in populations, while controlling for the role of general inbreeding. Before such evidence accumulates, captive breeding programs and other conservation measures aimed at inbreeding avoidance should be favoured over those protecting only MHC variation, especially since inbreeding avoidance programs would usually conserve both types of genetic diversity simultaneously.
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Affiliation(s)
- Jacek Radwan
- Institute of Nature Conservation, Polish Academy of Sciences, Al. Mickiewicza 33, 31-120 Kraków, Poland
| | - Aleksandra Biedrzycka
- Institute of Nature Conservation, Polish Academy of Sciences, Al. Mickiewicza 33, 31-120 Kraków, Poland
| | - Wiesław Babik
- Institute of Systematics and Evolution of Animals, Polish Academy of Sciences, Sławkowska 17, 31-016 Kraków, Poland
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126
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Tonteri A, Vasemägi A, Lumme J, Primmer CR. Beyond MHC: signals of elevated selection pressure on Atlantic salmon (Salmo salar) immune-relevant loci. Mol Ecol 2010; 19:1273-82. [PMID: 20196809 DOI: 10.1111/j.1365-294x.2010.04573.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Using Atlantic salmon (Salmo salar) as a model system, we investigated whether 18 microsatellites tightly linked to immune-relevant genes have experienced different selection pressures than 76 loci with no obvious association with immune function. Immune-relevant loci were identified as outliers by two outlier tests significantly more often than nonimmune linked loci (22% vs. 1.6%). In addition, the allele frequencies of immune relevant markers were more often correlated with latitude and temperature. Combined, these results support the hypothesis that immune-relevant loci more frequently exhibit footprints of selection than other loci. They also indicate that the correlation between immune-relevant loci and latitude may be due to temperature-induced differences in pathogen-driven selection or some other environmental factor correlated with latitude.
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Affiliation(s)
- A Tonteri
- Division of Genetics and Physiology, Department of Biology, University of Turku, FIN-20014 Turku, Finland
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127
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ALCAIDE MIGUEL, LEMUS JESÚSA, BLANCO GUILLERMO, TELLA JOSÉL, SERRANO DAVID, NEGRO JUANJ, RODRÍGUEZ AIRAM, GARCÍA-MONTIJANO MARINO. Retracted:MHC diversity and differential exposure to pathogens in kestrels (Aves:Falconidae). Mol Ecol 2010; 19:691-705. [DOI: 10.1111/j.1365-294x.2009.04507.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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128
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Schemske DW, Mittelbach GG, Cornell HV, Sobel JM, Roy K. Is There a Latitudinal Gradient in the Importance of Biotic Interactions? ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2009. [DOI: 10.1146/annurev.ecolsys.39.110707.173430] [Citation(s) in RCA: 808] [Impact Index Per Article: 53.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Douglas W. Schemske
- Department of Plant Biology and W.K. Kellogg Biological Station, Michigan State University, East Lansing, Michigan 48824;
| | - Gary G. Mittelbach
- W.K. Kellogg Biological Station and Department of Zoology, Michigan State University, Hickory Corners, Michigan 49060;
| | - Howard V. Cornell
- Department of Environmental Science and Policy, University of California, Davis, California 95616;
| | - James M. Sobel
- Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824;
| | - Kaustuv Roy
- Section of Ecology, Behavior, and Evolution, University of California, San Diego, La Jolla, California 92093;
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129
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Evans ML, Neff BD. Major histocompatibility complex heterozygote advantage and widespread bacterial infections in populations of Chinook salmon (Oncorhynchus tshawytscha). Mol Ecol 2009; 18:4716-29. [PMID: 19821902 DOI: 10.1111/j.1365-294x.2009.04374.x] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Despite growing evidence for parasite-mediated selection on the vertebrate major histocompatibility complex (MHC), little is known about variation in the bacterial parasite community within and among host populations or its influence on MHC evolution. In this study, we characterize variation in the parasitic bacterial community associated with Chinook salmon (Oncorhynchus tshawytscha) fry in five populations in British Columbia (BC), Canada across 2 years, and examine whether bacterial infections are a potential source of selection on the MHC. We found an unprecedented diversity of bacteria infecting fry with a total of 55 unique bacteria identified. Bacterial infection rates varied from 9% to 29% among populations and there was a significant isolation by distance relationship in bacterial community phylogenetic similarity across the populations. Spatial variation in the frequency of infections and in the phylogenetic similarity of bacterial communities may result in differential parasite-mediated selection at the MHC across populations. Across all populations, we found evidence of a heterozygote advantage at the MHC class II, which may be a source of balancing selection on this locus. Interestingly, a co-inertia analysis indicated only susceptibility associations between a few of the MHC class I and II alleles and specific bacterial parasites; there was no evidence that any of the alleles provided resistance to the bacteria. Our results reveal a complex bacterial community infecting populations of a fish and underscore the importance of considering the role of multiple pathogens in the evolution of host adaptations.
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Affiliation(s)
- Melissa L Evans
- Department of Biology, University of Western Ontario, 1151 Richmond St. N, London, ON, N6A 5B7, Canada
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130
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Diversity and evolution of MHII β genes in a non-model percid species—The Eurasian perch (Perca fluviatilis L.). Mol Immunol 2009; 46:3399-410. [DOI: 10.1016/j.molimm.2009.07.012] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2009] [Revised: 07/14/2009] [Accepted: 07/16/2009] [Indexed: 11/20/2022]
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131
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Evans ML, Neff BD, Heath DD. MHC genetic structure and divergence across populations of Chinook salmon (Oncorhynchus tshawytscha). Heredity (Edinb) 2009; 104:449-59. [PMID: 19773808 DOI: 10.1038/hdy.2009.121] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
The major histocompatibility complex (MHC) is thought to be under strong selection pressure because of its integral role in pathogen recognition. Consequently, patterns of MHC genetic variation should reflect selection pressures across the landscape. We examined genetic variation and population genetic structure at the MHC class I-A1 and class II-B1 exons in five Chinook salmon (Oncorhynchus tshawytscha) populations from two geographic regions in British Columbia, Canada. We then compared estimates of population structure at the MHC genes with neutral estimates based on microsatellites to examine the potential for local adaptation at the MHC. Chinook salmon are in decline throughout much of their native range and understanding the degree of local adaptation exhibited by the MHC may be important in conservation planning. Comparisons among populations yielded higher G'(ST) estimates for the MHC class I than expected under neutrality based on the microsatellites. In contrast, the MHC class II tended to exhibit lower G'(ST) values than did the microsatellites. These results suggest that across populations unique selection pressures are driving allele frequency differences at the MHC class I but that the MHC class II may be the subject of homogenizing selection. Rates of nonsynonymous versus synonymous substitutions found in codons associated within the MHC class I and II peptide-binding regions provided strong evidence of positive selection. Together, these results support the hypothesis that selection is influencing genetic variation at the MHC, but suggest that selection pressures may vary at the two classes of loci both at the sequence and population levels.
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Affiliation(s)
- M L Evans
- Department of Biology, University of Western Ontario, Ontario, Canada
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132
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Dionne M, Miller KM, Dodson JJ, Bernatchez L. MHC standing genetic variation and pathogen resistance in wild Atlantic salmon. Philos Trans R Soc Lond B Biol Sci 2009; 364:1555-65. [PMID: 19414470 DOI: 10.1098/rstb.2009.0011] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Pathogens are increasingly emerging in human-altered environments as a serious threat to biodiversity. In this context of rapid environmental changes, improving our knowledge on the interaction between ecology and evolution is critical. The objective of this study was to evaluate the influence of an immunocompetence gene, the major histocompatibility complex (MHC) class IIbeta, on the pathogen infection levels in wild Atlantic salmon populations, Salmo salar, and identify selective agents involved in contemporary coevolution. MHC variability and bacterial infection rate were determined throughout the summer in juvenile salmon from six rivers belonging to different genetic and ecological regions in Québec, Canada. A total of 13 different pathogens were identified in kidney by DNA sequence analysis, including a predominant myxozoa, most probably recently introduced in North America. Infection rates were the highest in southern rivers at the beginning of the summer (average 47.6+/-6.3% infected fish). One MHC allele conferred a 2.9 times greater chance of being resistant to myxozoa, while another allele increased susceptibility by 3.4 times. The decrease in frequency of the susceptibility allele but not other MHC or microsatellite alleles during summer was suggestive of a mortality event from myxozoa infection. These results supported the hypothesis of pathogen-driven selection in the wild by means of frequency-dependent selection or change in selection through time and space rather than heterozygous advantage, and underline the importance of MHC standing genetic variation for facing pathogens in a changing environment.
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Affiliation(s)
- Mélanie Dionne
- Département de Biologie, Université Laval, Québec, Canada.
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133
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Selection at the MHC class IIB locus across guppy (Poecilia reticulata) populations. Heredity (Edinb) 2009; 104:155-67. [DOI: 10.1038/hdy.2009.99] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
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134
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Tunsjø HS, Paulsen SM, Berg K, Sørum H, L'Abée-Lund TM. The winter ulcer bacterium Moritella viscosa demonstrates adhesion and cytotoxicity in a fish cell model. Microb Pathog 2009; 47:134-42. [PMID: 19539022 DOI: 10.1016/j.micpath.2009.06.005] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2009] [Revised: 05/28/2009] [Accepted: 06/04/2009] [Indexed: 10/20/2022]
Abstract
Moritella viscosa is considered the main aetiological agent of 'winter ulcer' disease in farmed salmonid fish. To further understand the pathogenesis of this disease, M. viscosa interaction with fish cells was studied using a Chinook salmon embryo cell line (CHSE-214). As winter ulcer appears exclusively at temperatures below 7-8 degrees C, we attempted to identify if this connection is explained by temperature regulated bacterial virulence. Therefore, infection studies were performed at a temperature range from 4 to 15 degrees C. At all temperatures, M. viscosa caused CHSE cells to retract and round up, lose their attachment abilities and finally disintegrate. The bacterium adhered to CHSE cells and caused changes to the cytoskeleton, however, it did not invade the cells. Increased adherence was demonstrated at 4 degrees C compared to adherence at higher temperatures. Extracellular proteins exerted rapid pore formation and lysis of CHSE cells at a temperature range from 4 to 22 degrees C. Furthermore, only small differences were found comparing extracellular proteomes of M. viscosa from 4 and 15 degrees C. We propose that the pathogenic mechanisms exerted by M. viscosa on CHSE cells are disruption of the cytoskeleton which affects cell rigidity and structure, followed by pore formation and lysis caused by secreted products from the bacterium. These processes can also occur at temperatures above those experienced from winter ulcer outbreaks. However, the adhesion mechanisms appear to be temperature regulated and may contribute to temperature dependent disease outbreaks.
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Affiliation(s)
- Hege Smith Tunsjø
- Norwegian School of Veterinary Science, Department of Food Safety and Infection Biology, Oslo, Norway.
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135
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Kekäläinen J, Vallunen JA, Primmer CR, Rättyä J, Taskinen J. Signals of major histocompatibility complex overdominance in a wild salmonid population. Proc Biol Sci 2009; 276:3133-40. [PMID: 19515657 DOI: 10.1098/rspb.2009.0727] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The major histocompatibility complex (MHC) contains the most variable genes in vertebrates, but despite extensive research, the mechanisms maintaining this polymorphism are still unresolved. One hypothesis is that MHC polymorphism is a result of balancing selection operating by overdominance, but convincing evidence for overdominant selection in natural populations has been lacking. We present strong evidence consistent with MHC-specific overdominance in a free-living population of Arctic charr (Salvelinus alpinus) in northernmost Europe. In this population, where just two MHC alleles were observed, MHC heterozygous fish had a lower parasite load, were in better condition (as estimated by a fatness indicator) and had higher survival under stress than either of the homozygotes. Conversely, there was no consistent association between these fitness measures and assumedly neutral microsatellite variability, indicating an MHC-specific effect. Our results provide convincing empirical evidence consistent with the notion that overdominance can be an important evolutionary mechanism contributing to MHC polymorphism in wild animal populations. They also support a recent simulation study indicating that the number of alleles expected to be maintained at an MHC loci can be low, even under strong heterozygote advantage.
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Affiliation(s)
- Jukka Kekäläinen
- Department of Biological and Environmental Science, University of Jyväskylä, PO Box 35 (YAC-315.2), 40014 Jyväskylä, Finland.
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136
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Yeates SE, Einum S, Fleming IA, Megens HJ, Stet RJ, Hindar K, Holt WV, Van Look KJ, Gage MJ. Atlantic salmon eggs favour sperm in competition that have similar major histocompatibility alleles. Proc Biol Sci 2009; 276:559-66. [PMID: 18854296 PMCID: PMC2592554 DOI: 10.1098/rspb.2008.1257] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2008] [Accepted: 09/23/2008] [Indexed: 12/02/2022] Open
Abstract
Polyandry and post-copulatory sexual selection provide opportunities for the evolution of female differential sperm selection. Here, we examined the influence of variation in major histocompatibility (MH) class I allelic composition upon sperm competition dynamics in Atlantic salmon. We ran in vitro fertilization competitions that mimicked the gametic microenvironment, and replicated a paired-male experimental design that allowed us to compare differences in sperm competition success among males when their sperm compete for eggs from females that were genetically either similar or dissimilar at the MH class I locus. Concurrently, we measured variation in spermatozoal traits that are known to influence relative fertilization success under these conditions. Contrary to the findings demonstrating mechanisms that promote MH complex heterozygosity, our results showed that males won significantly greater relative fertilization success when competing for eggs from genetically similar females at the MH class I. This result also showed covariation with the known influences of sperm velocity on relative fertilization success. We discuss these unexpected findings in relation to sperm-egg recognition and hybridization avoidance mechanisms based upon immunogenetic variation.
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Affiliation(s)
- Sarah E. Yeates
- School of Biological Sciences, Norwich Research Park, University of East AngliaNorwich NR4 7TJ, UK
| | - Sigurd Einum
- Department of Biology, Norwegian University of Science and Technology, NO-7491Tungasletta 2, 7485 Trondheim, Norway
| | - Ian A. Fleming
- Ocean Sciences Centre, Memorial University of NewfoundlandSt. John's, Newfoundland, Canada A1C 5S7
| | - Hendrik-Jan Megens
- Animal Breeding and Genomics Centre, Wageningen UniversityPO Box 338, 6700AH Wageningen, The Netherlands
| | - René J.M. Stet
- Cell Biology and Immunology Group, Wageningen Agricultural UniversityPO Box 9101, 6700 HB Wageningen, The Netherlands
| | - Kjetil Hindar
- Department of Biology, Norwegian University of Science and Technology, NO-7491Tungasletta 2, 7485 Trondheim, Norway
| | - William V. Holt
- Institute of Zoology, Zoological Society of LondonRegent's Park, London NW1 4RY, UK
| | | | - Matthew J.G. Gage
- School of Biological Sciences, Norwich Research Park, University of East AngliaNorwich NR4 7TJ, UK
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137
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Hutchinson WF. The dangers of ignoring stock complexity in fishery management: the case of the North Sea cod. Biol Lett 2009; 4:693-5. [PMID: 18782730 DOI: 10.1098/rsbl.2008.0443] [Citation(s) in RCA: 98] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The plight of the marine fisheries is attracting increasing attention as unsustainably high exploitation levels, exacerbated by more extreme climatic conditions, are driving stocks to the point of collapse. The North Atlantic cod (Gadus morhua), a species which until recently formed a major component of the demersal fisheries, has undergone significant declines across its range. The North Sea stock is typical of many, with a spawning stock biomass that has remained below the safe biological limit since 2000 and recruitment levels near the lowest on record. Cod within the North Sea are currently managed as a single stock, and yet mounting empirical evidence supports the existence of a metapopulation of regionally variable, genetically distinct, sub-stocks. Applying the same management strategies to multiple stocks that differ in their resilience to exploitation inevitably results in the overfishing and likely collapse of the weaker components. Indeed, recent studies have identified two North Sea spawning stocks that have undergone disproportionally large collapses with very substantial reductions in egg production. Similarly affected cod stocks in the northwest Atlantic have shown little evidence of recovery, despite fishery closures. The possible implications of ignoring sub-structuring within management units for biocomplexity, local adaptation and ecosystem stability are considered.
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138
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Cheviron ZA, Brumfield RT. Migration-selection balance and local adaptation of mitochondrial haplotypes in rufous-collared sparrows (Zonotrichia capensis) along an elevational gradient. Evolution 2009; 63:1593-605. [PMID: 19187247 DOI: 10.1111/j.1558-5646.2009.00644.x] [Citation(s) in RCA: 116] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Variable selection pressures across heterogeneous landscapes can lead to local adaptation of populations. The extent of local adaptation depends on the interplay between natural selection and gene flow, but the nature of this relationship is complex. Gene flow can constrain local adaptation by eroding differentiation driven by natural selection, or local adaptation can itself constrain gene flow through selection against maladapted immigrants. Here we test for evidence that natural selection constrains gene flow among populations of a widespread passerine bird (Zonotrichia capensis) that are distributed along an elevational gradient in the Peruvian Andes. Using multilocus sequences and microsatellites screened in 142 individuals collected along a series of replicate transects, we found that mitochondrial gene flow was significantly reduced along elevational transects relative to latitudinal control transects. Nuclear gene flow, however, was not similarly reduced. Clines in mitochondrial haplotype frequency were strongly associated with transitions in environmental variables along the elevational transects, but this association was not observed for the nuclear markers. These results suggest that natural selection constrains mitochondrial gene flow along elevational gradients and that the mitonuclear discrepancy may be due to local adaptation of mitochondrial haplotypes.
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Affiliation(s)
- Zachary A Cheviron
- Louisiana State University Museum of Natural Science, 119 Foster Hall, Baton Rouge, Louisiana 70803, USA.
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139
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Turner SM, Chaves-Campos J, DeWoody JA. Parental relatedness and major histocompatibility effects on early embryo survivorship in Atlantic salmon. Genetica 2009; 137:99-109. [PMID: 19184462 DOI: 10.1007/s10709-009-9354-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2008] [Accepted: 01/16/2009] [Indexed: 11/29/2022]
Abstract
Salmon have provided key insights into the relative influence of natural and sexual selection on major histocompatibility complex (MHC) variation. Natural selection on salmon MHC genes has been demonstrated in pathogen studies, and there is evidence of MHC-based mate choice (sexual selection). We tested whether parental MHC genes affect survivorship of juvenile Atlantic salmon (Salmo salar) by quantifying the influence of parental genome-wide relatedness and MHC genotype on survivorship to the swim-up stage. Thirteen microsatellite loci were used to estimate the influence of genome-wide relatedness between parents on offspring survivorship and MHC genotypes were determined by sequencing part of the class IIbeta gene. Our results revealed no significant relationship between early offspring survivorship and genome-wide relatedness, predicted MHC heterozygosity, or MHC allelic similarity. Overall, our data are consistent with the contention that excess MHC heterozygosity in Atlantic salmon juveniles is due to sexual selection as well as differential survival of offspring due to MHC genotype.
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Affiliation(s)
- Sara M Turner
- Department of Forestry and Natural Resources, Purdue University, West Lafayette, IN 47907, USA.
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140
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Oliver MK, Lambin X, Cornulier T, Piertney SB. Spatio-temporal variation in the strength and mode of selection acting on major histocompatibility complex diversity in water vole (Arvicola terrestris) metapopulations. Mol Ecol 2009; 18:80-92. [PMID: 19140966 DOI: 10.1111/j.1365-294x.2008.04015.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Patterns of spatio-temporal genetic variation at a class II major histocompatibility complex (MHC) locus and multiple microsatellite loci were analysed within and between three water vole metapopulations in Scotland, UK. Comparisons of MHC and microsatellite spatial genetic differentiation, based on standardised tests between two demographically asynchronous zones within a metapopulation, suggested that spatial MHC variation was affected by balancing selection, directional selection and random genetic drift, but that the relative effects of these microevolutionary forces vary temporally. At the metapopulation level, between-year differentiation for MHC loci was significantly correlated with that of microsatellites, signifying that neutral factors such as migration and drift were primarily responsible for overall temporal genetic change at the metapopulation scale. Between metapopulations, patterns of genetic differentiation implied that, at large spatial scales, MHC variation was primarily affected by directional selection and drift. Levels of MHC heterozygosity in excess of Hardy-Weinberg expectations were consistent with overdominant balancing selection operating on MHC variation within metapopulations. However, this effect was not constant among all samples, indicating temporal variation in the strength of selection relative to other factors. The results highlight the benefit of contrasting variation at MHC with neutral markers to separate the effects of stochastic and deterministic microevolutionary forces, and add to a growing body of evidence showing that the mode and relative strength of selection acting on MHC diversity varies both spatially and temporally.
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Affiliation(s)
- Matthew K Oliver
- School of Biological Sciences, University of Aberdeen, Zoology Building, Aberdeen AB24 2TZ, Scotland, UK.
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141
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Comparative survey of within-river genetic structure in Atlantic salmon; relevance for management and conservation. CONSERV GENET 2008. [DOI: 10.1007/s10592-008-9647-5] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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142
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Croisetière S, Tarte PD, Bernatchez L, Belhumeur P. Identification of MHC class IIβ resistance/susceptibility alleles to Aeromonas salmonicida in brook charr (Salvelinus fontinalis). Mol Immunol 2008; 45:3107-16. [PMID: 18455800 DOI: 10.1016/j.molimm.2008.03.007] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2008] [Revised: 03/07/2008] [Accepted: 03/10/2008] [Indexed: 10/22/2022]
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143
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Wegner KM, Kalbe M, Milinski M, Reusch TB. Mortality selection during the 2003 European heat wave in three-spined sticklebacks: effects of parasites and MHC genotype. BMC Evol Biol 2008; 8:124. [PMID: 18447901 PMCID: PMC2386451 DOI: 10.1186/1471-2148-8-124] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2008] [Accepted: 04/30/2008] [Indexed: 11/10/2022] Open
Abstract
Background Ecological interaction strength may increase under environmental stress including temperature. How such stress enhances and interacts with parasite selection is almost unknown. We studied the importance of resistance genes of the major histocompatibility complex (MHC) class II in 14 families of three-spined sticklebacks Gasterosteus aculeatus exposed to their natural macroparasites in field enclosures in the extreme summer of 2003. Results After a mass die-off during the 2003-European heat wave killing 78% of 277 experimental fish, we found strong differences in survival among and within families. In families with higher average parasite load fewer individuals survived. Multivariate analysis revealed that the composition of the infecting parasite fauna was family specific. Within families, individuals with an intermediate number of MHC class IIB sequence variants survived best and had the lowest parasite load among survivors, suggesting a direct functional link between MHC diversity and fitness. The within family MHC effects were, however, small compared to between family effects, suggesting that other genetic components or non-genetic effects were also important. Conclusion The correlation between parasite load and mortality that we found at both individual and family level might have appeared only in the extraordinary heatwave of 2003. Due to global warming the frequency of extreme climatic events is predicted to increase, which might intensify costs of parasitism and enhance selection on immune genes.
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Affiliation(s)
- K Mathias Wegner
- Department of Integrative Biology (IBZ), Experimental Ecology, ETH Zürich, Universitätstrasse 16, CH - 8092 Zürich, Switzerland.
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144
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Dionne M, Caron F, Dodson JJ, Bernatchez L. Landscape genetics and hierarchical genetic structure in Atlantic salmon: the interaction of gene flow and local adaptation. Mol Ecol 2008; 17:2382-96. [PMID: 18430145 DOI: 10.1111/j.1365-294x.2008.03771.x] [Citation(s) in RCA: 176] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Disentangling evolutionary forces that may interact to determine the patterns of genetic differentiation within and among wild populations is a major challenge in evolutionary biology. The objective of this study was to assess the genetic structure and the potential influence of several ecological variables on the extent of genetic differentiation at multiple spatial scales in a widely distributed species, the Atlantic salmon, Salmo salar. A total of 2775 anadromous fish were sampled from 51 rivers along the North American Atlantic coast and were genotyped using 13 microsatellites. A Bayesian analysis clustered these populations into seven genetically and geographically distinct groups, characterized by different environmental and ecological factors, mainly temperature. These groups were also characterized by different extent of genetic differentiation among populations. Dispersal was relatively high and of the same magnitude within compared to among regional groups, which contrasted with the maintenance of a regional genetic structure. However, genetic differentiation was lower among populations exchanging similar rates of local as opposed to inter-regional migrants, over the same geographical scale. This raised the hypothesis that gene flow could be constrained by local adaptation at the regional scale. Both coastal distance and temperature regime were found to influence the observed genetic structure according to landscape genetic analyses. The influence of other factors such as latitude, river length and altitude, migration tactic, and stocking was not significant at any spatial scale. Overall, these results suggested that the interaction between gene flow and thermal regime adaptation mainly explained the hierarchical genetic structure observed among Atlantic salmon populations.
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Affiliation(s)
- Mélanie Dionne
- Département de Biologie, Université Laval, Québec, Canada G1V 0A6.
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