| 1. |
- Arlt, D, et al.
(författare)
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Observation of a ZZW female in a natural population: implications for avian sex determination
- 2004
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Ingår i: Royal Society of London. Proceedings B. Biological Sciences. - : The Royal Society. - 1471-2954. ; 271:S4, s. 249-251
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Tidskriftsartikel (refereegranskat)abstract
- Avian sex determination is chromosomal; however, the underlying mechanisms are not yet understood. There is no conclusive evidence for either of two proposed mechanisms: a dominant genetic switch or a dosage mechanism. No dominant sex-determining gene on the female-specific W chromosome has been found. Birds lack inactivation of one of the Z chromosomes in males, but seem to compensate for a double dose of Z-linked genes by other mechanisms. Recent studies showing female-specific expression of two genes may support an active role of the W chromosome. To resolve the question of avian sex determination the investigation of birds with a 2A: ZZW or 2A: Z0 genotype would be decisive. Here, we report the case of an apparent 2A: ZZW great reed warbler (Acrocephalus arundinaceus) female breeding in a natural population, which was detected using Z-linked microsatellites. Our data strongly suggest a role of W-linked genes in avian sex determination.
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| 2. |
- Bensch, Staffan, et al.
(författare)
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Host specificity in avian blood parasites: a study of Plasmodium and Haemoproteus mitochondrial DNA amplified from birds
- 2000
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Ingår i: Royal Society of London. Proceedings B. Biological Sciences. - : The Royal Society. - 1471-2954. ; 267:1452, s. 1583-1589
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Tidskriftsartikel (refereegranskat)abstract
- A fragment of the mitochondrial cytochrome b gene of avian malaria (genera Haemoproteus and Plasmodium) was amplified from blood samples of 12 species of passerine birds from the genera Acrocephalus, Phylloscopus and Parus. By sequencing 478 nucleotides of the obtained fragments, we found 17 different mitocholdrial haplotypes of Haemoproteus or Plasmodium among the 12 bird species investigated. Only one out of the: 17 haplotypes was found in more than one host species, this exception being a haplotype detected in both blue tits (Parus caeruleus) and great tits (Parus major). The phylogenetic tree which was constructed grouped the sequences into two clades, most probably representing Haemoproteus and Plasmodium, respectively. We found two to four different parasite mitochondrial DNA (mtDNA) haplotypes in four bird species. The phylogenetic tree obtained from the mtDNA of the parasites matched the phylogenetic tree of the bird hosts poorly For example, the two tit species and the willow warbler (Phylloscopus troclilus) carried parasites differing by only 0.6% sequence divergence, suggesting that Haemoproteus shift both between species within the same genus and also between species in different families. Hence, host shifts seem to have occurred repeatedly in this parasite-host system. We discuss this in terms of the possilble evolutionary consequences for these bird species.
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| 3. |
- Bonneaud, C, et al.
(författare)
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Diversity of Mhc class I and IIB genes in house sparrows (Passer domesticus)
- 2004
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Ingår i: Immunogenetics. - : Springer Science and Business Media LLC. - 1432-1211 .- 0093-7711. ; 55:12, s. 855-865
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In order to understand the expression and evolution of host resistance to pathogens, we need to examine the links between genetic variability at the major histocompatibility complex (Mhc), phenotypic expression of the immune response and parasite resistance in natural populations. To do so, we characterized the Mhc class I and IIB genes of house sparrows with the goal of designing a PCR-based genotyping method for the Mhc genes using denaturing gradient gel electrophoresis (DGGE). The incredible success of house sparrows in colonizing habitats worldwide allows us to assess the importance of the variability of Mhc genes in the face of various pathogenic pressures. Isolation and sequencing of Mhc class I and IIB alleles revealed that house sparrows have fewer loci and fewer alleles than great reed warblers. In addition, the Mhc class I genes divided in two distinct lineages with different levels of polymorphism, possibly indicating different functional roles for each gene family. This organization is reminiscent of the chicken B complex and Rfp-Y system. The house sparrow Mhc hence appears to be intermediate between the great reed warbler and the chicken Mhc, both in terms of numbers of alleles and existence of within-class lineages. We specifically amplified one Mhc class I gene family and ran the PCR products on DGGE gels. The individuals screened displayed between one and ten DGGE bands, indicating that this method can be used in future studies to explore the ecological impacts of Mhc diversity.
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| 4. |
- Bonneaud, C, et al.
(författare)
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Terminal investment induced by immune challenge and fitness traits associated with major histocompatibility complex in the house sparrow
- 2004
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Ingår i: Evolution. - 1558-5646. ; 58:12, s. 2823-2830
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Tidskriftsartikel (refereegranskat)abstract
- The terminal investment hypothesis predicts that individuals should invest more in their present reproduction if they are less likely to survive to future reproductive events. Infections, which reduce viability, may be used by individuals as a cue of a diminishing residual reproductive value and could therefore theoretically trigger an intensification of breeding effort. We tested this hypothesis in a natural population of house sparrows (Passer domesticus). We manipulated the immune system of breeding females by injecting them with a vaccine against the Paramyxo virus, the agent of Newcastle disease. Females were captured and treated immediately after completion of their first clutch either with the vaccine (NDV) or with phosphate buffered saline (PBS). The entire clutch was subsequently removed. We also screened Mhc class I genes of females to assess possible genotype-by-immune treatment interactions on reproductive investment. Our results indicate that vaccinated females were more likely to lay replacement clutches and that the difference in number of eggs between first and replacement clutches was greater for NDV females than for controls. In addition, chick size, both in terms of tarsus length and body mass, was affected by immune activation but in interaction with nestling age and female body mass, respectively. Mhc genotype-by-immune treatment interactions were never significant; however, allelic diversity was positively correlated with nestling survival. These results show that immune system activation is potentially used as a cue of reduced survival prospect and appears to induce a costly terminal investment behavior, and Mhc diversity might be under selection in a natural population of house sparrows.
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| 5. |
- Hansson, Bengt, et al.
(författare)
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Does linkage disequilibrium generate heterozygosity-fitness correlations in great reed warblers?
- 2004
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Ingår i: Evolution. - 1558-5646. ; 58:4, s. 870-879
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Tidskriftsartikel (refereegranskat)abstract
- Heterozygosity-fitness correlations (HFCs) at noncoding genetic markers are commonly assumed to reflect fitness effects of heterozygosity at genomewide distributed genes in partially inbred populations. However, in populations with much linkage disequilibrium (LD), HFCs may arise also as a consequence of selection on fitness loci in the local chromosomal vicinity of the markers. Recent data suggest that relatively high levels of LD may prevail in many ecological situations. Consequently, LD may be an important factor, together with partial inbreeding, in causing HFCs in natural populations. In the present study, we evaluate whether LD can generate HFCs in a small and newly founded population of great reed warblers (Acrocephalus arundinaceus). For this purpose dyads of full siblings of which only one individual survived to adult age (i.e., returned to breed at the study area) were scored at 19 microsatellite loci, and at a gene region of hypothesized importance for survival, the major histocompatibility complex (MHC). By examining siblings, we controlled for variation in the inbreeding coefficient and thus excluded genome-wide fitness effects in our analyses. We found that recruited individuals had significantly higher multilocus heterozygosity (MLH), and mean d(2) (a microsatellite-specific variable), than their nonrecruited siblings. There was a tendency for the survivors to have a more diverse MHC than the nonsurvivors. Single-locus analyses showed that the strength of the genotype-survival association was especially pronounced at four microsatellite loci. By using genotype data from the entire breeding population, we detected significant LD between five of 162 pairs of microsatellite loci after accounting for multiple tests. Our present finding of a significant within-family multilocus heterozygosity-survival association in a nonequilibrium population supports the view that LD generates HFCs in natural populations.
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| 6. |
- Richardson, David, et al.
(författare)
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MHC diversity in two Acrocephalus species: the outbred Great reed warbler and the inbred Seychelles warbler
- 2003
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Ingår i: Molecular Ecology. - 0962-1083. ; 12:12, s. 3523-3529
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Tidskriftsartikel (refereegranskat)abstract
- The Great reed warbler (GRW) and the Seychelles warbler (SW) are congeners with markedly different demographic histories. The GRW is a normal outbred bird species while the SW population remains isolated and inbred after undergoing a severe population bottleneck. We examined variation at Major Histocompatibility Complex (MHC) class I exon 3 using restriction fragment length polymorphism, denaturing gradient gel electrophoresis and DNA sequencing. Although genetic variation was higher in the GRW, considerable variation has been maintained in the SW. The ten exon 3 sequences found in the SW were as diverged from each other as were a random sub-sample of the 67 sequences from the GRW. There was evidence for balancing selection in both species, and the phylogenetic analysis showing that the exon 3 sequences did not separate according to species, was consistent with transspecies evolution of the MHC.
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| 7. |
- Westerdahl, Helena
(författare)
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Avian MHC: variation and selection in the wild
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In vertebrates the Major Histocompatibility Complex (MHC) plays a central role in the specific immune defence against various pathogens. Compared with other coding genes the MHC genes exhibit an extremely high level of polymorphism that is maintained by balancing selection. The importance in the immune defence and the polymorphism make these genes interesting to study from an ecological and evolutionary perspective in populations subject to natural selection. In my thesis I have studied MHC in a population of wild songbirds, great reed warblers Acrocephalus arundinaceus. Firstly, I characterized parts of the MHC class I and II genes and I focused especially on transcribed genes since these are likely to be under selection. Then I developed a PCR-based screening method for investigating the MHC class I polymorphism in our study population. In the great reed warbler genome there was a large number of MHC class I and II genes and there was also evidence of balancing selection in these genes. There was a surprisingly high level of variation in the MHC genes in the great reed warblers within the study population considering the limited variation that have been detected using neutral markers. Secondly, I searched for evidence of selection on the MHC genes and for associations between life-history data and MHC genes. I found evidence that there is selection on the MHC class I alleles in great reed warblers. Avian malaria could be one such selective force since great reed warblers that had a large number of MHC alleles (heterozygous individuals) survived an infection with avian malaria (GRW2) more often than individuals with fewer MHC alleles. Hence, a large number of MHC alleles seem critical for survival. However, we did not find that MHC-compatibility is involved in female mate choice in the great reed warblers, as has been found in humans and mice, despite the fact that more MHC heterozygous great reed warbler siblings do survive more often. Finally, associations between certain MHC alleles, or a large number of MHC alleles, and resistance to specific diseases have so far been found in a handful of species. Most of these associations involve humans or are experiments that have been done under controlled conditions. To me it is compelling that the selection pressure from pathogens on MHC genes can be visualised also under natural conditions in wild populations, as e.g. the great reed warblers.
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| 8. |
- Westerdahl, Helena, et al.
(författare)
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Between-year variation of MHC allele frequencies in great reed warblers: selection or drift?
- 2004
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Ingår i: Journal of evolutionary biology. - : Wiley. - 1420-9101 .- 1010-061X. ; 17:3, s. 485-492
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Tidskriftsartikel (refereegranskat)abstract
- The major histocompatibility complex (MHC) genes are extremely polymorphic and this variation is assumed to be maintained by balancing selection. Cyclic interactions between pathogens and their hosts could generate such selection, and specific MHC alleles or heterozygosity at certain MHC loci have been shown to confer resistance against particular pathogens. Here we compare the temporal variation in allele frequencies of 23 MHC class I alleles with that of 23 neutral microsatellite markers in adult great reed warblers (a passerine bird) in nine successive cohorts. Overall, the MHC alleles showed a significantly higher variation in allele frequencies between cohorts than the microsatellite alleles, using a multi-variate genetic analysis (AMOVA). The frequency of two specific MHC alleles, A3e (P = 0.046) and B4b (P = 0.0018), varied more between cohorts than expected from random, whereas none of the microsatellite alleles showed fluctuations exceeding the expectation from stochastic variation. These results imply that the variation in MHC allele frequencies between cohorts is not a result of demographic events, but rather an effect of selection favouring different MHC alleles in different years.
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| 9. |
- Westerdahl, Helena, et al.
(författare)
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Brood sex ratios, female harem status and resources for nestling provisioning in the great reed warbler (Acrocephalus arundinaceus)
- 2000
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Ingår i: Behavioral Ecology and Sociobiology. - : Springer Science and Business Media LLC. - 1432-0762 .- 0340-5443. ; 47:5, s. 312-318
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Tidskriftsartikel (refereegranskat)abstract
- The theory of parental investment and brood sex ratio manipulation predicts that parents should invest in the more costly sex during conditions when resources are abundant. In the polygynous great reed warbler, Acrocephalus arundinaceus. females of primary harem status have more resources for nestling provisioning than secondary females, because polygynous males predominantly assist the primary female whereas the secondary female has to feed her young alone. Sons weigh significantly more than daughters, and are hence likely to be the more costly sex. In the present study, we measured the brood sex ratio when the chicks were 9 days old, i.e. the fledging sex ratio. As expected from theory, we found that female great reed warblers of primary status had a higher proportion of sons in their broods than females of lower (secondary) harem status. This pattern is in accordance with the results from two other species of marsh-nesting polygynous birds, the oriental reed warbler, Acrocephalus orientalis, and the yellow-headed blackbird Xanthocephalus xanthocephalus. As in the oriental reed warbler, we found that great reed warbler males increased their share of parental care as the proportion of sons in the brood increased. We did not find any difference in fitness of sons and daughters raised in primary and secondary nests. The occurrence of adaptive sex ratio manipulations in birds has been questioned, and it is therefore important that three studies of polygynous bird species, including our own, have demonstrated the same pattern of a male-biased offspring sex ratio in primary compared with secondary nests.
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| 10. |
- Westerdahl, Helena, et al.
(författare)
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MHC class I typing in a songbird with numerous loci and high polymorphism using motif-specific PCR and DGGE
- 2004
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Ingår i: Heredity. - : Springer Science and Business Media LLC. - 1365-2540 .- 0018-067X. ; 92:6, s. 534-542
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Tidskriftsartikel (refereegranskat)abstract
- The major histocompatibility complex (MHC) has a central role in the specific immune defence of vertebrates. Exon 3 of MHC class I genes encodes the domain that binds and presents peptides from pathogens that trigger immune reactions. Here we develop a fast population screening method for detecting genetic variation in the MHC class I genes of birds. We found evidence of at least 15 exon 3 sequences in the investigated great reed warbler individual. The organisation of the great reed warbler MHC class I genes suggested that a locus-specific screening protocol is impractical due to the high similarity between alleles across loci, including the introns flanking exon 3. Therefore, we used motif-specific PCR to amplify two subsets of alleles ( exon 3 sequences) that were separated with by DGGE. The motif-specific primers amplify a substantial proportion of the transcribed class I alleles (2-12 alleles per individual) from as many as six class I loci. Although not exhaustive, this gives a reliable estimate of the class I variation. The method is highly repeatable and more sensitive in detecting genetic variation than the RFLP method. The motif-specific primers also allow us to avoid screening pseudogenes. In our study population of great reed warblers, we found a high level of genetic variation in MHC class I, and no less than 234 DGGE genotypes were detected among 248 screened individuals.
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