scholarly journals Natural Selection on MHC IIb in Parapatric Lake and Stream Stickleback: Balancing, Divergent, Both, or Neither?

2016 ◽  
Author(s):  
William E. Stutz ◽  
Daniel I. Bolnick
Keyword(s):  
Allelic Variation ◽  
Balancing Selection ◽  
Divergent Selection ◽  
Parasite Communities ◽  
Mhc Genes ◽  
Mhc Polymorphism ◽  
Novel Strategy ◽  
Spatially Varying ◽  
Mhc Alleles ◽  
Mhc Iib

AbstractMajor histocompatibility (MHC) genes encode proteins that play a central role in vertebrates’ adaptive immunity to parasites. MHC loci are among the most polymorphic in vertebrates’ genomes, inspiring many studies to identify evolutionary processes driving MHC polymorphism within populations, and divergence between populations. Leading hypotheses include balancing selection favoring rare alleles within populations, and spatially divergent selection. These hypotheses do not always produce diagnosably distinct predictions, causing many studies of MHC to yield inconsistent or ambiguous results. We suggest a novel strategy to distinguish balancing versus divergent selection on MHC, taking advantage of natural admixture between parapatric populations. With divergent selection, immigrant alleles will be more infected and less fit because they are susceptible to novel parasites in their new habitat. With balancing selection, locally-rare immigrant alleles will be more fit (less infected). We tested these contrasting predictions using threespine stickleback from three replicate pairs of parapatric lake and stream habitats. We found numerous positive and negative associations between particular MHC IIβ alleles and particular parasite taxa. A few allele-parasite comparisons supported balancing selection, others supported divergent selection between habitats. But, there was no overall tendency for fish with immigrant MHC alleles to be more or less heavily infected. Instead, locally rare MHC alleles (not necessarily immigrants) were associated with heavier infections. Our results illustrate the complex relationship between MHC IIβ allelic variation and spatially varying multi-species parasite communities: different hypotheses may be concurrently true for different allele-parasite combinations.

scholarly journals Diversity of MHC IIB genes and parasitism in hybrids of evolutionarily divergent cyprinoid species indicate heterosis advantage

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Andrea Šimková ◽  
Lenka Gettová ◽  
Kristína Civáňová ◽  
Mária Seifertová ◽  
Michal Janáč ◽  
...  
Keyword(s):  
Seasonal Effect ◽  
Parasite Communities ◽  
Histocompatibility Complex ◽  
Interspecies Hybrids ◽  
Allele Expression ◽  
In The Wild ◽  
Species Specific ◽  
Mhc Alleles ◽  
Mhc Iib ◽  
Mhc Supertypes

AbstractThe genes of the major histocompatibility complex (MHC) are an essential component of the vertebrate immune system and MHC genotypes may determine individual susceptibility to parasite infection. In the wild, selection that favors MHC variability can create situations in which interspecies hybrids experience a survival advantage. In a wild system of two naturally hybridizing leuciscid fish, we assessed MHC IIB genetic variability and its potential relationships to hosts’ ectoparasite communities. High proportions of MHC alleles and parasites were species-specific. Strong positive selection at specific MHC codons was detected in both species and hybrids. MHC allele expression in hybrids was slightly biased towards the maternal species. Controlling for a strong seasonal effect on parasite communities, we found no clear associations between host-specific parasites and MHC alleles or MHC supertypes. Hybrids shared more MHC alleles with the more MHC-diverse parental species, but expressed intermediate numbers of MHC alleles and positively selected sites. Hybrids carried significantly fewer ectoparasites than either parent species, suggesting a hybrid advantage via potential heterosis.

scholarly journals Chasing the genes that control resistance to gastrointestinal nematodes

2003 ◽  
Vol 77 (2) ◽  
pp. 99-109 ◽  
Author(s):  
J.M. Behnke ◽  
F. Iraqi ◽  
D. Menge ◽  
R.L. Baker ◽  
J. Gibson ◽  
...  
Keyword(s):  
Immune Response ◽  
Egg Production ◽  
Allelic Variation ◽  
Control Strategies ◽  
Domestic Animals ◽  
Gastrointestinal Nematodes ◽  
Comparative Genomic ◽  
Human Beings ◽  
Signalling Molecules ◽  
Mhc Genes

AbstractThe host-protective immune response to infection with gastrointestinal (GI) nematodes involves a range of interacting processes that begin with recognition of the parasite's antigens and culminate in an inflammatory reaction in the intestinal mucosa. Precisely which immune effectors are responsible for the loss of specific worms is still not known although many candidate effectors have been proposed. However, it is now clear that many different genes regulate the response and that differences between hosts (fast or strong versus slow or weak responses) can be explained by allelic variation in crucial genes associated with the gene cascade that accompanies the immune response and/or genes encoding constitutively expressed receptor/signalling molecules. Major histocompatibility complex (MHC) genes have been recognized for some time as decisive in controlling immunity, and evidence that non-MHC genes are equally, if not more important in this respect has also been available for two decades. Nevertheless, whilst the former have been mapped in mice, only two candidate loci have been proposed for non-MHC genes and relatively little is known about their roles. Now, with the availability of microsatellite markers, it is possible to exploit linkage mapping techniques to identify quantitative trait loci (QTL) responsible for resistance to GI nematodes. Four QTL for resistance to Heligmosomoides polygyrus, and additional QTL affecting faecal egg production by the worms and the accompanying immune responses, have been identified. Fine mapping and eventually the identification of the genes (and their alleles) underlying QTL for resistance/susceptibility will permit informed searches for homologues in domestic animals, and human beings, through comparative genomic maps. This information in turn will facilitate targeted breeding to improve resistance in domestic animals and, in human beings, focused application of treatment and control strategies for GI nematodes.

Balancing selection, sexual selection and geographic structure in MHC genes of Great Snipe

Genetica ◽  
2008 ◽  
Vol 138 (4) ◽  
pp. 453-461 ◽  
Author(s):  
Robert Ekblom ◽  
Stein Are Sæther ◽  
Peder Fiske ◽  
John Atle Kålås ◽  
Jacob Höglund
Keyword(s):  
Sexual Selection ◽  
Balancing Selection ◽  
Mhc Genes ◽  
Geographic Structure

scholarly journals Effects of Population Bottleneck and Balancing Selection on the Chinese Alligator Are Revealed by Locus-Specific Characterization of MHC Genes

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
Teng Zhai ◽  
Hai-Qiong Yang ◽  
Rui-Can Zhang ◽  
Li-Ming Fang ◽  
Guo-Heng Zhong ◽  
...  
Keyword(s):  
Balancing Selection ◽  
Population Bottleneck ◽  
Mhc Genes ◽  
Chinese Alligator

scholarly journals Diversity and selection of MHC class I genes in the Godlewski's bunting

2020 ◽  
Author(s):  
Wei Huang ◽  
Boye Liu ◽  
Tobias Lenz ◽  
Yangyang Peng ◽  
Yan-Yun Zhang ◽  
...  
Keyword(s):  
Amino Acid ◽  
Mhc Class I ◽  
Biological Diversity ◽  
Balancing Selection ◽  
Class I ◽  
Immune Gene ◽  
Amino Acid Polymorphism ◽  
Mountain Area ◽  
Mhc Genes ◽  
High Amino Acid

The major histocompatibility complex (MHC) is a multiple-copy immune gene family in vertebrates. Its genes are highly variable and code for antigen-presenting molecules. Characterization of MHC genes in different species and investigating the mechanisms that shape MHC diversity is an important goal in understanding the evolution of biological diversity. Here we developed a next generation sequencing (NGS) protocol to genotype the MHC class I genes of 326 Godlewski’s buntings (Emberiza godlewskii) sampled in the Western mountain area of Beijing from 2014 to 2016. A total of 184 functional alleles were identified, including both non-classical and classical alleles. Classical alleles could be clustered into nine supertypes. Compared with other passerine birds, the individual diversity of MHC class I genes in Godlewski’s buntings is intermediate. Ten amino acid sites in the antigen-binding domain showed signatures of positive selection and eight of them exhibit high amino acid polymorphism. These findings indicate the action of balancing selection and provide a framework for subsequent investigation of selection acting on MHC genes in Godlewski’s buntings.

scholarly journals Diverse Functions Associate With Non-Coding Trans-species Polymorphisms in Humans

2021 ◽  
Author(s):  
Keila Velazquez-Arcelay ◽  
Mary Lauren Benton ◽  
John A. Capra
Keyword(s):  
Immune System ◽  
Allelic Variation ◽  
Balancing Selection ◽  
Association Studies ◽  
Regulatory Function ◽  
Genome Wide Association Studies ◽  
Functional Annotations ◽  
Coding Regions ◽  
Genome Wide ◽  
Mhc Locus

Abstract Background: Long-term balancing selection (LTBS) can maintain allelic variation at a locus over millions of years and through speciation events. Variants shared between species, hereafter “trans-species polymorphisms” (TSPs), often result from LTBS due to host-pathogen interactions. For instance, the major histocompatibility complex (MHC) locus contains TSPs present across primates. Several hundred candidate TSPs have been identified in humans and chimpanzees; however, because many are in non-coding regions of the genome, the functions and adaptive roles for most TSPs remain unknown. Results: We integrated diverse genomic annotations, with a focus on non-coding regions, to explore the functions of 125 previously identified regions containing multiple TSPs in humans and chimpanzees. We analyzed genome-wide functional assays, expression quantitative trait loci (eQTL), genome-wide association studies (GWAS), and phenome-wide association studies (PheWAS). We identify functional annotations for 119 TSP regions, including 71 with evidence of gene regulatory function from GTEx or genome-wide functional genomics data and 21 with evidence of trait association from GWAS and PheWAS. TSPs in humans associate with many immune system phenotypes, including response to pathogens, but we also find associations with a range of other phenotypes, including body mass, alcohol intake, urate levels, chronotype, and risk-taking behavior. Conclusions: The diversity of traits associated with non-coding human TSPs further support previous hypotheses that functions beyond the immune system are subject to LTBS. Furthermore, several of these trait associations provide support and candidate genetic loci for previous hypothesis about behavioral diversity in great ape populations, such as the importance of variation in sleep cycles and risk sensitivity.

scholarly journals Associations between malaria and MHC genes in a migratory songbird

2005 ◽  
Vol 272 (1571) ◽  
pp. 1511-1518 ◽  
Author(s):  
Helena Westerdahl ◽  
Jonas Waldenström ◽  
Bengt Hansson ◽  
Dennis Hasselquist ◽  
Torbjörn von Schantz ◽  
...  
Keyword(s):  
Positive Association ◽  
Malaria Parasites ◽  
Mhc Genes ◽  
Long Term Study ◽  
Histocompatibility Complex ◽  
Study Population ◽  
Migratory Songbird ◽  
Avian Populations ◽  
Mhc Alleles

Malaria parasites are a widespread and species-rich group infecting many wild populations of mammals, birds and reptiles. Studies on humans have demonstrated that genetic factors play a key role in the susceptibility and outcome of malaria infections. Until the present study, it has not been examined whether genetic variation in hosts is important for the outcome of malaria infections in natural avian populations. We investigated associations between major histocompatibility complex (MHC) genes and prevalence of three different avian malaria parasites ( Haemoproteus payevskyi (GRW1), Plasmodium sp. (GRW2) and Plasmodium sp. (GRW4)) in a long-term study of great reed warblers Acrocephalus arundinaceus . We hypothesized that the MHC genes could either give full protection against a malaria infection, or confer protection against lethal malaria and direct the infection towards being milder. We found a positive association between numbers of MHC class I alleles (a measure of level of heterozygosity) and prevalence of the GRW2 parasite, suggesting the latter scenario. There was also a positive association between a specific MHC allele (B4b), previously shown to be under frequency-dependent selection in the study population, and prevalence of GRW2. These associations suggest that individuals carrying either a large number of MHC alleles or a specific MHC allele are protected against lethal malaria infections.

scholarly journals Allelic diversity and patterns of selection at the major histocompatibility complex class I and II loci in a threatened shorebird, the Snowy Plover (Charadrius nivosus)

2020 ◽  
Vol 20 (1) ◽  
Author(s):  
Medardo Cruz-López ◽  
Guillermo Fernández ◽  
Helen Hipperson ◽  
Eduardo Palacios ◽  
John Cavitt ◽  
...  
Keyword(s):  
Mhc Class I ◽  
Mhc Class Ii ◽  
Balancing Selection ◽  
Allelic Diversity ◽  
Class Ii ◽  
Class I ◽  
Mhc Genes ◽  
Snowy Plover ◽  
Snowy Plovers ◽  
Private Alleles

Abstract Background Understanding the structure and variability of adaptive loci such as the major histocompatibility complex (MHC) genes is a primary research goal for evolutionary and conservation genetics. Typically, classical MHC genes show high polymorphism and are under strong balancing selection, as their products trigger the adaptive immune response in vertebrates. Here, we assess the allelic diversity and patterns of selection for MHC class I and class II loci in a threatened shorebird with highly flexible mating and parental care behaviour, the Snowy Plover (Charadrius nivosus) across its broad geographic range. Results We determined the allelic and nucleotide diversity for MHC class I and class II genes using samples of 250 individuals from eight breeding population of Snowy Plovers. We found 40 alleles at MHC class I and six alleles at MHC class II, with individuals carrying two to seven different alleles (mean 3.70) at MHC class I and up to two alleles (mean 1.45) at MHC class II. Diversity was higher in the peptide-binding region, which suggests balancing selection. The MHC class I locus showed stronger signatures of both positive and negative selection than the MHC class II locus. Most alleles were present in more than one population. If present, private alleles generally occurred at very low frequencies in each population, except for the private alleles of MHC class I in one island population (Puerto Rico, lineage tenuirostris). Conclusion Snowy Plovers exhibited an intermediate level of diversity at the MHC, similar to that reported in other Charadriiformes. The differences found in the patterns of selection between the class I and II loci are consistent with the hypothesis that different mechanisms shape the sequence evolution of MHC class I and class II genes. The rarity of private alleles across populations is consistent with high natal and breeding dispersal and the low genetic structure previously observed at neutral genetic markers in this species.

The role of infectious disease, inbreeding and mating preferences in maintaining MHC genetic diversity: an experimental test

1994 ◽  
Vol 346 (1317) ◽  
pp. 369-378 ◽  
Keyword(s):  
Genetic Diversity ◽  
Balancing Selection ◽  
Natural Populations ◽  
House Mice ◽  
Heterozygote Advantage ◽  
Immune Recognition ◽  
Mating Preferences ◽  
Conventional View ◽  
Mhc Genes ◽  
Allele Specific

In house mice, and probably most mammals, major histocompatibility complex (MHC) gene products influence both immune recognition and individual odours in an allele-specific fashion. Although it is generally assumed that some form of pathogen-driven balancing selection is responsible for the unprecedented genetic diversity of MHC genes, the MHC-based mating preferences observed in house mice are sufficient to account for the genetic diversity of MHC genes found in this and other vertebrates. These MHC disassortative mating preferences are completely consistent with the conventional view that pathogen-driven MHC heterozygote advantage operates on MHC genes. This is because such matings preferentially produce MHC-heterozygours progeny, which could enjoy enhanced disease resistance. However, such matings could also function to avoid genome-wide inbreeding. To discriminate between these two hypotheses we measured the fitness consequences of both experimentally manipulated levels of inbreeding and MHC homozygosity and heterozygosity in semi-natural populations of wild-derived house mice. We were able to measure a fitness decline associated with inbreeding, but were unable to detect fitness declines associated with MHC homozygosity. These data suggest that inbreeding avoidance may be the most important function of MHC-based mating preferences and therefore the fundamental selective force diversifying MHC genes in species with such mating patterns. Although controversial, this conclusion is consistent with the majority of the data from the inbreeding and immunological literature.

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