scholarly journals Borrelia Infection in Bank Voles Myodes glareolus Is Associated With Specific DQB Haplotypes Which Affect Allelic Divergence Within Individuals

2021 ◽  
Vol 12 ◽  
Author(s):  
Kristin Scherman ◽  
Lars Råberg ◽  
Helena Westerdahl
Keyword(s):  
Mhc Class Ii ◽  
Balancing Selection ◽  
Sequence Divergence ◽  
Myodes Glareolus ◽  
Heterozygote Advantage ◽  
Allelic Polymorphism ◽  
Risk Of Infection ◽  
Fluctuating Selection ◽  
Bank Voles ◽  
Infection Resistance

The high polymorphism of Major Histocompatibility Complex (MHC) genes is generally considered to be a result of pathogen-mediated balancing selection. Such selection may operate in the form of heterozygote advantage, and/or through specific MHC allele–pathogen interactions. Specific MHC allele–pathogen interactions may promote polymorphism via negative frequency-dependent selection (NFDS), or selection that varies in time and/or space because of variability in the composition of the pathogen community (fluctuating selection; FS). In addition, divergent allele advantage (DAA) may act on top of these forms of balancing selection, explaining the high sequence divergence between MHC alleles. DAA has primarily been thought of as an extension of heterozygote advantage. However, DAA could also work in concert with NFDS though this is yet to be tested explicitly. To evaluate the importance of DAA in pathogen-mediated balancing selection, we surveyed allelic polymorphism of MHC class II DQB genes in wild bank voles (Myodes glareolus) and tested for associations between DQB haplotypes and infection by Borrelia afzelii, a tick-transmitted bacterium causing Lyme disease in humans. We found two significant associations between DQB haplotypes and infection status: one haplotype was associated with lower risk of infection (resistance), while another was associated with higher risk of infection (susceptibility). Interestingly, allelic divergence within individuals was higher for voles with the resistance haplotype compared to other voles. In contrast, allelic divergence was lower for voles with the susceptibility haplotype than other voles. The pattern of higher allelic divergence in individuals with the resistance haplotype is consistent with NFDS favouring divergent alleles in a natural population, hence selection where DAA works in concert with NFDS.

scholarly journals Genotype-environment interaction and the maintenance of genetic variation: an empirical study of Lobelia inflata (Campanulaceae)

2020 ◽  
Vol 7 (3) ◽  
pp. 191720 ◽  
Author(s):  
Kristen Côté ◽  
Andrew M. Simons
Keyword(s):  
Genetic Variation ◽  
Balancing Selection ◽  
Rank Order ◽  
Empirical Test ◽  
Heterozygote Advantage ◽  
Environment Interaction ◽  
Fluctuating Selection ◽  
Long Term Study ◽  
Genotype Environment Interaction ◽  
Lobelia Inflata

High levels of genetic variation are often observed in natural populations, suggesting the action of processes such as frequency-dependent selection, heterozygote advantage and variable selection. However, the maintenance of genetic variation in fitness-related traits remains incompletely explained. The extent of genetic variation in obligately self-fertilizing populations of Lobelia inflata (Campanulaceae L.) strongly implies balancing selection. Lobelia inflata thus offers an exceptional opportunity for an empirical test of genotype-environment interaction (G × E) as a variance-maintaining mechanism under fluctuating selection: L. inflata is monocarpic and reproduces only by seed, facilitating assessment of lifetime fitness; genome-wide homozygosity precludes some mechanisms of balancing selection, and microsatellites are, in effect, genotypic lineage markers. Here, we find support for the temporal G × E hypothesis using a manipulated space-for-time approach across four environments: a field environment, an outdoor experimental plot and two differing growth-chamber environments. High genetic variance was confirmed: 83 field-collected individuals consisted of 45 distinct microsatellite lineages with, on average, 4.5 alleles per locus. Rank-order fitness, measured as lifetime fruit production in 16 replicated multilocus genotypes, changed significantly across environments. Phenotypic differences among microsatellite lineages were detected. Results thus support the G × E hypothesis in principle. However, the evaluation of the effect size of this mechanism and fitness effects of life-history traits will require a long-term study of fluctuating selection on labelled genotypes in the field.

MHC reflects fine-scale habitat structure in white-tailed eagles Haliaeetus albicilla

2021 ◽  
Author(s):  
Piotr Minias ◽  
Aleksandra Janiszewska ◽  
Ewa Pikus ◽  
Tomasz Zadworny ◽  
Dariusz Anderwald
Keyword(s):  
Mhc Class I ◽  
Mhc Class Ii ◽  
Habitat Structure ◽  
Balancing Selection ◽  
Strong Support ◽  
Class Ii ◽  
Class I ◽  
Fluctuating Selection ◽  
Haliaeetus Albicilla ◽  
Habitat Variation

Abstract The Major Histocompatibility Complex (MHC) genes code for key immune receptors responsible for recognition of intra- and extra-cellular pathogens (MHC class I and class II, respectively). It was hypothesized that MHC polymorphism can be maintained via fluctuating selection resulting from between-habitat variation in pathogen regimes. We examined associations between MHC class I and class II genes and habitat structure in an apex avian predator, the white-tailed eagle Haliaeetus albicilla. We genotyped MHC class I and class II genes in ca. 150 white-tailed eagle chicks from nearly one hundred nesting territories distributed across three distinct populations in Poland. Habitat structure was quantified at the levels of foraging territories and directly at the nest sites. We found strong support for associations of habitat traits with diversity and allelic composition at the MHC class II. Forest area within territory and forest productivity were identified as the major habitat predictors of MHC class II polymorphism, while other habitat traits (distance to nearest open water, grassland and water area within territory or understory presence) showed fewer associations with class II alleles. In contrast, there was little support for associations between MHC class I genes and habitat structure. All significant associations were apparent at the within- rather than between-population level. Our results suggest that extra-cellular (rather than intra-cellular) pathogens may exert much stronger selective pressure on the white-tailed eagle. Associations of habitat structure with MHC class II may reflect fluctuating (balancing) selection which maintains MHC diversity within populations.

scholarly journals Contemporary evolution of the viral-sensing TLR3 gene in an isolated vertebrate population

2021 ◽  
Author(s):  
Charli Davies ◽  
Martin Taylor ◽  
Martijn Hammers ◽  
Terry Burke ◽  
J Komdeur ◽  
...  
Keyword(s):  
Positive Selection ◽  
Balancing Selection ◽  
Extended Period ◽  
Lifetime Reproductive Success ◽  
Heterozygote Advantage ◽  
Contemporary Evolution ◽  
Fluctuating Selection ◽  
Functional Variation ◽  
Evolutionary Forces ◽  
Tlr3 Gene

Understanding where and how genetic variation is maintained within populations is important from an evolutionary and conservation perspective. Signatures of past selection suggest that pathogen-mediated balancing selection is a key driver of immunogenetic variation, but studies tracking contemporary evolution are needed to help resolve the evolutionary forces and mechanism at play. Previous work in a bottlenecked population of Seychelles warblers (Acrocephalus sechellensis) show that functional variation has been maintained at the viral-sensing Toll-like receptor 3 (TLR3) gene. Here, we characterise evolution at this TLR3 locus over a 25-year period within the original remnant population of the Seychelles warbler, and in four other derived, contained populations. Results show a significant and consistent temporal decline in the frequency of the TLR3C allele in the original population, and that similar declines in the TLR3C allele frequency occurred in all the derived populations. Individuals (of both sexes) with the TLR3CC genotype had lower survival, and males - but not females - that carry the TLR3C allele had significantly lower lifetime reproductive success than those with only the TLR3A allele. These results indicate that positive selection, caused by an as yet unknown agent, is driving TLR3 evolution in the Seychelles warblers. No evidence of heterozygote advantage was detected. However, whether the positive selection observed is part of a longer-term pattern of balancing selection (through fluctuating selection or rare-allele advantage) cannot be resolved without tracking the TLR3C allele in the populations over an extended period of time.

scholarly journals A rare MHC haplotype confers selective advantage in a free-living ruminant

2020 ◽  
Author(s):  
Wei Huang ◽  
Kara L Dicks ◽  
Jarrod D Hadfield ◽  
Susan E Johnston ◽  
Keith T Ballingall ◽  
...  
Keyword(s):  
Life Span ◽  
Mhc Class Ii ◽  
Balancing Selection ◽  
Natural Populations ◽  
Class Ii ◽  
Ovis Aries ◽  
Fluctuating Selection ◽  
Soay Sheep ◽  
Mhc Genes ◽  
Mhc Class Ii Genes

AbstractThe major histocompatibility complex (MHC) is the most variable gene family known in vertebrates. Parasite-mediated selection (PMS) is believed to be the main force maintaining diversity at MHC genes, but it has proven hard to demonstrate the exact PMS regime that is acting in natural populations. Demonstrating contemporary selection on MHC alleles is not trivial, and previous work has been constrained by limited genetic tools, low sample sizes, short time scales and anticonservative statistical approaches. Here, we use a conservative statistical approach to examine associations between MHC genes and fitness components, using haplotypes of expressed MHC class II genes in a large sample of Soay sheep (Ovis aries) monitored over their lifetimes between 1989 and 2012. Of the eight MHC haplotypes (A-H) identified, we found that haplotype C was associated with decreased male breeding success, haplotype D was associated with increased female life span, and haplotype F was associated with decreased female life span. Consistent with the increased lifespan in females, haplotype D has increased in frequency throughout the study period. Our results suggest the existence of contemporary balancing selection on MHC class II genes in Soay sheep as might be expected under the hypotheses of rare allele advantage or fluctuating selection and do not support an effect of heterozygous advantage.

A Chromosomal Region Promoting Outcrossing in a Conifer

Genetics ◽  
2001 ◽  
Vol 159 (3) ◽  
pp. 1283-1289
Author(s):  
Claire G Williams ◽  
Yi Zhou ◽  
Sarah E Hall
Keyword(s):  
Linkage Group ◽  
Chromosomal Region ◽  
Expressed Sequence Tag ◽  
Balancing Selection ◽  
Lethal Factor ◽  
Genetic Mechanism ◽  
Heterozygote Advantage ◽  
Experimental Profile ◽  
Gametic Selection ◽  
Pinus Taeda L

Abstract Prefertilization mechanisms influencing selfing rates are thought to be absent in conifers. Outcrossing in conifers is promoted via an embryo-lethal system, but the genetic mechanism is poorly understood. This study is the first experimental profile of the genetic mechanism promoting outcrossing in conifers. Molecular dissection of a Pinus taeda L. selfed pedigree detected a chromosomal region identified as PtTX3020-RPtest9. Within this region, a semilethal factor was tightly linked (r = 0.0076) to a polymorphic expressed sequence tag (EST). The linkage group flanking the lethal factor showed strong heterozygote advantage. Using genotypic frequencies for the linkage group, three hypotheses about the semilethal factor could be tested: (1) the presence of a balanced lethal system, i.e., a lethal factor present in each of the two marker intervals; (2) gametic selection operative prior to fertilization; and (3) a stage-specific lethal factor. Selection acted via the embryo-lethal system. No support for a genetic mechanism operating prior to fertilization was found. The semilethal factor exerted no effect after embryo maturity. The genetic mechanism promoting outcrossing in P. taeda L. appears to have a balancing selection system due to either pseudo-overdominance or true overdominance.

scholarly journals When does parasitism maintain sex in the absence of Red Queen Dynamics?

2020 ◽  
Author(s):  
Ben Ashby
Keyword(s):  
Population Density ◽  
Sexual Reproduction ◽  
Evolutionary Model ◽  
Niche Overlap ◽  
Disease Prevalence ◽  
Heterozygote Advantage ◽  
Red Queen ◽  
Fluctuating Selection ◽  
Antagonistic Coevolution ◽  
Maintenance Of Sex

AbstractParasites can select for sexual reproduction in host populations, preventing replacement by faster growing asexual lineages. This is usually attributed to so-called “Red Queen Dynamics” (RQD), where antagonistic coevolution causes fluctuating selection in allele frequencies, which provides sex with an advantage over asex. However, parasitism may also maintain sex in the absence of RQD when sexual populations are more genetically diverse – and hence more resistant, on average – than clonal populations, allowing sex and asex to stably coexist. While the maintenance of sex due to RQD has been studied extensively, the conditions that allow sex and asex to stably coexist have yet to be explored in detail. In particular, we lack an understanding of how host demography and parasite epidemiology affect the maintenance of sex in the absence of RQD. Here, I use an eco-evolutionary model to show that both population density and the type and strength of virulence are important for maintaining sex, which can be understood in terms of their effects on disease prevalence and severity. In addition, I show that even in the absence of heterozygote advantage, asexual heterozygosity affects coexistence with sex due to variation in niche overlap. These results reveal which host and parasite characteristics are most important for the maintenance of sex in the absence of RQD, and provide empirically testable predictions for how demography and epidemiology mediate competition between sex and asex.

scholarly journals Seroprevalence of Toxoplasma gondii among sylvatic rodents in Poland

2021 ◽  
Author(s):  
Maciej Grzybek ◽  
Daniela Antolová ◽  
Katarzyna Tołkacz ◽  
Mohammed Alsarraf ◽  
Jolanta Behnke-Borowczyk ◽  
...  
Keyword(s):  
Toxoplasma Gondii ◽  
Rodent Species ◽  
Myodes Glareolus ◽  
Host Age ◽  
Bank Voles ◽  
Vole Species ◽  
Age And Sex

ABSTRACTToxoplasma gondii is a significant pathogen affecting humans and animals. We conducted seromonitoring for T. gondii in four sylvatic rodent species in Poland. We report an overall seroprevalence of 5.5% (3.6% for Myodes glareolus and 20% for other vole species). Seroprevalence in bank voles varied significantly between host age and sex.

Sign in / Sign up

Export Citation Format

Share Document