| 1. |
- Ekblom, Robert, et al.
(author)
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Balancing selection, sexual selection and geographic structure in MHC genes of Great Snipe
- 2010
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In: Genetica. - : Springer Science and Business Media LLC. - 0016-6707 .- 1573-6857. ; 138:4, s. 453-461
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Journal article (peer-reviewed)abstract
- Signatures of balancing selection are often found when investigating the extremely polymorphic regions of major histocompatibility complex (MHC) genes, and it is generally accepted that selective forces maintain this polymorphism. However, the exact nature of the selection is controversial. Theoretical studies have mainly focused on overdominance and/or frequency dependent selection while laboratory studies have emphasised the role of mate choice. Empirical field data, on the other hand, have been relatively scarce. Previously we have found that geographic structure in MHC class II genes of the Great Snipe (Gallinago media) is too pronounced to be explained by neutral forces alone. Here we test the hypothesis that sexual selection on MHC alleles may be influencing this geographic structure between mountain and lowland populations. We found evidence of balancing selection acting on MHC genes in the form of a higher rate of amino-acid changing substitutions compared to silent substitutions in the peptide binding regions. Not only natural selection but also sexual selection may influence MHC polymorphism in this bird because certain MHC alleles have been found to be associated with higher male mating success. Contrary to predictions from negative frequency dependent selection, males carrying locally rare alleles did not have a mating advantage. Instead, the mating success of alleles in a mountain population was positively correlated to their relative frequency in the mountains compared to the lowlands, implying that locally adapted MHC alleles may also be favoured by sexual selection.
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| 2. |
- Ekblom, Robert, et al.
(author)
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Female choice and male humoral immune response in the lekking great snipe (Gallinago media)
- 2005
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In: Behavioral Ecology. - : Oxford University Press (OUP). - 1045-2249 .- 1465-7279. ; 16:2, s. 346-351
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Journal article (peer-reviewed)abstract
- Parasites and diseases constitute major evolutionary forces in many natural populations, and thus having an efficient immune defense to resist infections is crucial for many organisms. Properties of the immune response may also influence mate choice decisions in many animals. Theory predicts several advantages for females when choosing males with superior immune systems. These benefits can be both direct (e.g. increased paternal care and reduced disease transmission) and indirect (good genes). We have investigated female choice with respect to antibody response to two novel antigens in males of a lekking bird, the great snipe (Gallinago media). Because of the lek mating system, female choice probably mainly incurs indirect (genetic) rather than direct benefits. Males responded to vaccination with diphtheria and tetanus toxoids by producing specific antibodies to both antigens. Triggering the immune system had no negative impact on display activities or survival. Males that were chosen by females as mates had on average higher antibody response to the tetanus antigen than their neighbors. We did not, however, find any covariance between the strength of the antibody response and male mating success.
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| 3. |
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| 4. |
- Ekblom, Robert, 1976-
(author)
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Immunoecology of the Great Snipe (Gallinago media) : Mate Choice, MHC Variation, and Humoral Immunocompetence in a Lekking Bird
- 2004
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Doctoral thesis (other academic/artistic)abstract
- At the centre of the vertebrate immune system is a group of proteins called MHC (major histocompatibility complex) molecules. These function in self – non self recognition and activation of the immune defence against intruding parasites and pathogens. In this thesis I have investigated individual variation in MHC class II genes and antibody producing ability in relation to ecology and behaviour in the great snipe (Gallinago media), a lekking bird, breeding in northern Europe. There was much variation in the MHC genes of the great snipe and the sequence data show that balancing selection has been acting on these genes. I found genetic differentiation in the MHC between two separate geographic regions of the great snipe distribution. Furthermore, this structure was more pronounced than that previously found in neutral genetic markers, suggesting that different selection pressures (possibly resulting from variation in parasitic fauna) are acting in these different regions. The birds produced specific antibodies following injection with two novel antigens. Males that were chosen as mates, had higher antibody titers than their neighbouring males, suggesting that this ability may be important in female mate choice. Such choice could give the offspring an enhanced immune system or could favour females directly by avoidance of sexually transmitted diseases. Females choosing to mate with a male having a different set of MHC genes than their own could give the offspring immune system the ability to react to a wide range of parasites. No such mate choice could, however, be found in the great snipe. Instead, females preferred males with certain MHC alleles, irrespective of their own MHC type. If those alleles confer resistance to parasites currently prevailing in the population, such resistance would be inherited by the offspring, thereby enhancing their fitness.
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| 5. |
- Ekblom, Robert, et al.
(author)
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Major histocompatibility complex variation and mate choice in a lekking bird, the great snipe (Gallinago media)
- 2004
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In: Molecular Ecology. - 0962-1083 .- 1365-294X. ; 13:12, s. 3821-3828
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Journal article (peer-reviewed)abstract
- Genes of the major histocompatibility complex (MHC) play a major part in the activation of the vertebrate immune system. In addition, they also appear to function as cues for mate choice. In mammals especially, several kinds of MHC-dependent mate choice have been hypothesized and observed. These include choice of mates that share no or few alleles with the choosing individual, choice of mates with alleles that differ as much as possible from the choosing individual, choice of heterozygous mates, choice of certain genotypes and choice of rare alleles. We investigated these different aspects of mate choice in relation to MHC in a lekking bird species, the great snipe (Gallinago media). We found no evidence for MHC disassortative mating, no preference for males with many MHC alleles and no preference for rare alleles. However, we did find that some allelic lineages were more often found in males with mating success than in males without mating success. Females do not seem to use themselves as references for the MHC-dependent mate choice, rather they seem to prefer males with certain allele types. We speculate that these alleles may be linked to resistance to common parasites.
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| 6. |
- Ekblom, Robert, et al.
(author)
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Patterns of polymorphism in the MHC class II of a non-passerine bird, the great snipe (Gallinago media)
- 2003
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In: Immunogenetics. - : Springer Science and Business Media LLC. - 0093-7711 .- 1432-1211. ; 54:10, s. 734-741
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Journal article (peer-reviewed)abstract
- The genomic organisation of the major histocompatibility complex (MHC) seems to vary considerably between different bird species. In order to understand this variation it is important to gather information from different species. We have, for the first time, investigated MHC class 11 polymorphism in a wader species, the great snipe (Gallinago media). Eleven alleles were found in five sequenced individuals; these come from at least three different loci, but RFLP data suggest that a larger number of genes may be present. For MHC genes, amino acid substitutions followed the, for MHC genes, general pattern of high non-synonymous substitution rates in peptide-binding regions, suggesting that the sequenced alleles may be expressed. The number of genes, lengths of introns and exon sequences of the great snipe MHC seem to be intermediate between those of chicken and passerine birds.
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| 7. |
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| 8. |
- Ekblom, Robert, et al.
(author)
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Spatial pattern of MHC class II variation in the great snipe (Gallinago media)
- 2007
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In: Molecular Ecology. - 0962-1083 .- 1365-294X. ; 16:7, s. 1439-1451
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Journal article (peer-reviewed)abstract
- The genes of the major histocompatibility complex (MHC) code for proteins involved in antigen recognition and triggering of the adaptive immune response, and are therefore likely to be under selection from parasites. These selection regimes may vary in space and time. Here we report a strong geographical structure in MHC class II B genes of a migrating bird, the great snipe (Gallinago media). Genetic differentiation in the MHC between two ecologically distinct distributional regions (Scandinavian mountain populations vs. East European lowland populations) was still present after statistically controlling for the effect of selectively neutral variation (microsatellites) using partial Mantel tests. This suggests a role for selection in generating this spatial structure and that it represents local adaptation to different environments. Differentiation between populations within the two regions was negligible. Overall, we found a high number of MHC alleles (50, from 175 individuals). This, together with a tendency for a higher rate of nonsynonymous than synonymous substitutions in the peptide binding sites, and high Tajima's D in certain regions of the gene, suggests a history of balancing selection. MHC variation is often thought to be maintained by some form of balancing selection, but the nature of this selection remains unclear. Our results support the hypothesis that spatial variation in selection regimes contributes to the high polymorphism.
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| 9. |
- Höglund, Jacob, et al.
(author)
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Blood transcriptomes and de novo identification of candidate loci for mating success in lekking great snipe (Gallinago media)
- 2017
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In: Molecular Ecology. - : Wiley. - 0962-1083 .- 1365-294X. ; 26:13, s. 3458-3471
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Journal article (peer-reviewed)abstract
- We assembled the great snipe blood transcriptome using data from fourteen lekking males, in order to de novo identify candidate genes related to sexual selection, and determined the expression profiles in relation to mating success. The three most highly transcribed genes were encoding different haemoglobin subunits. All tended to be overexpressed in males with high mating success. We also called single nucleotide polymorphisms (SNPs) from the transcriptome data and found considerable genetic variation for many genes expressed during lekking. Among these, we identified 14 polymorphic candidate SNPs that had a significant genotypic association with mating success (number of females mated with) and/or mating status (mated or not). Four of the candidate SNPs were found in HBAA (encoding the haemoglobin a-chain). Heterozygotes for one of these and one SNP in the gene PABPC1 appeared to enjoy higher mating success compared to males homozygous for either of the alleles. In a larger data set of individuals, we genotyped 38 of the identified SNPs but found low support for consistent selection as only one of the zygosities of previously identified candidate SNPs and none of their genotypes were associated with mating status. However, candidate SNPs generally showed lower levels of spatial genetic structure compared to noncandidate markers. We also scored the prevalence of avian malaria in a subsample of birds. Males infected with avian malaria parasites had lower mating success in the year of sampling than noninfected males. Parasite infection and its interaction with specific genes may thus affect performance on the lek.
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| 10. |
- Saether, Stein Are, et al.
(author)
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Direct and indirect mate choice on leks.
- 2005
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In: The American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 166, s. 145-157
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Journal article (peer-reviewed)
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