| 1. |
- von Schantz, Torbjörn, et al.
(författare)
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Artificial selection for increased comb size and its effects on other sexual characters and viability in gallus-domesticus (the domestic chicken)
- 1995
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Ingår i: Heredity. - : Springer Science and Business Media LLC. - 1365-2540 .- 0018-067X. ; 75:5, s. 518-529
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Tidskriftsartikel (refereegranskat)abstract
- The expression of secondary ornaments is often positively correlated with the bearer's condition. So far no study has reported on consequences of directional selection on male sexual ornaments in birds, i.e. it is unknown to what extent male sexual traits are genetically correlated and whether selection for secondary ornaments affects viability. In this study we estimate phenotypic and genotypic parameters of three male sexual traits, namely comb size, spur length and testes mass, by using two different lines of domestic chickens (Gallus domesticus). One of the two lines had been artificially selected for large comb size during nine generations whereas the other line was a randomly mated control line. As a result of the selection, male comb size was almost doubled. Data from the selection line indicate that comb size was negatively genetically correlated with testes mass and spur length. The cockerels from the selection line had accordingly lighter testes and shorter spurs than cockerels from the control line. A simple mate choice experiment with females and males from both lines indicated that preferred males had a larger joint expression of comb size and spur length than nonpreferred males. Data from three different selection lines, all with enlarged comb size, clearly reveal a negative effect of comb size on male viability.
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| 2. |
- von Schantz, Torbjörn, et al.
(författare)
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Good genes, oxidative stress and condition-dependent sexual signals
- 1999
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Ingår i: Royal Society of London. Proceedings B. Biological Sciences. - : The Royal Society. - 1471-2954 .- 0962-8452. ; 266:1, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- The immune and the detoxication systems of animals are characterized by allelic polymorphisms, which underlie individual differences in ability to combat assaults from pathogens and toxic compounds. Previous studies have shown that females may improve offspring survival by selecting mates on the basis of sexual ornaments and signals that honestly reveal health. In many cases the expression of these ornaments appears to be particularly sensitive to oxidative stress. Activated immune and detoxication systems often generate oxidative stress by an extensive production of reactive metabolites and free radicals. Given that tolerance or resistance to toxic compounds and pathogens can be inherited, female choice should promote the evolution of male ornaments that reliably reveal the status of the bearers' level of oxidative stress. Hence, oxidative stress may be one important agent linking the expression of sexual ornaments to genetic variation in fitness-related traits, thus promoting the evolution of female mate choice and male sexual ornamentation, a controversial issue in evolutionary biology ever since Darwin.
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| 3. |
- von Schantz, Torbjörn, et al.
(författare)
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Mate choice, male condition-dependent ornamentation and MHC in the pheasant
- 1997
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Ingår i: Hereditas. - : Springer Science and Business Media LLC. - 1601-5223 .- 0018-0661. ; 127:2, s. 133-140
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Tidskriftsartikel (refereegranskat)abstract
- The Hamilton and Zuk model predicts that genes for resistance to various pathogens may be continuously heritable due to selection disequilibria caused by coadaptional cycles of hosts and pathogens. The model further suggests that the expression of male secondary ornaments is condition-dependent and that only individuals with superior genetic disease resistance and vigour can fully express exaggerated secondary ornaments. Female choice is therefore expected to discriminate among males on the basis of secondary sexual characters in order to pass on genes for disease resistance that improve fitness in the offspring. In wild ring-necked pheasants, Phasianus colchicus, of the Revinge area in southern Sweden, females prefer to mate with long-spurred males and data on reproductive success indicate that they may improve their chicks' survival rate by doing so. Male spur length is positively correlated with age, body size and viability. MHC genotyping for both class I and class II B of pheasant males trapped in the study area identified eight MHC haplotypes and a total of 17 different MHC genotypes. Multivariate analyses revealed that MHC genotype is significantly associated with variation in both male spur length and male viability. These data indicate that polymorphic genes with a central role in immune recognition can be associated with viability and the expression of a condition-dependent intersexually selected male trait, thus supporting essential parts of the Hamilton and Zuk model.
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| 4. |
- von Schantz, Torbjörn, et al.
(författare)
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MHC genotype and male ornamentation: Genetic evidence for the Hamilton-Zuk model
- 1996
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Ingår i: Royal Society of London. Proceedings B. Biological Sciences. - : The Royal Society. - 1471-2954. ; 263:1368, s. 265-271
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Tidskriftsartikel (refereegranskat)abstract
- The major histocompatibility complex (MHC) is an immunologically important cluster of highly variable genes that is known to affect fitness in domesticated mammals and birds. Spur length of male pheasants in southern Sweden correlates with male viability, female mate choice, and offspring survival rate. Here we show by genetic analyses that the MHC genotype is associated with variation in both male spur length and male viability. These are the first data that directly support a 'good genes' hypothesis by Hamilton and Zuk predicting that females discriminate among males on the basis of secondary sexual characters in order to pass on genes for disease resistance that improve fitness in their offspring.
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| 5. |
- Westerdahl, Helena, et al.
(författare)
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Polymorphism and transcription of Mhc class I genes in a passerine bird, the great reed warbler
- 1999
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Ingår i: Immunogenetics. - : Springer Science and Business Media LLC. - 1432-1211 .- 0093-7711. ; 49:3, s. 158-170
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Tidskriftsartikel (refereegranskat)abstract
- The class I genes of the major histocompatibility complex (Mhc) are here investigated for the first time in a passerine bird. The great reed warbler is a rare species in Sweden with a few semi-isolated populations. Yet, we found extensive Mhc class I variation in the study population. The variable exon 3, corresponding to the alpha(2) domain, was amplified from genomic DNA with degenerated primers. Seven different genomic class I sequences were detected in a single individual. One of the sequences had a deletion leading to a shift in the reading frame, indicating that it was not a functional gene. A randomly selected clone was used as a probe for restriction fragment length polymorphism (RFLP) studies in combination with the restriction enzyme Pvu II. The RFLP pattern was complex with 21-25 RFLP fragments per individual and extensive variation. Forty-nine RFLP genotypes were detected in 55 tested individuals. To study the number of transcribed genes, we isolated 14 Mhc class I clones from a cDNA library from a single individual. We found eight different sequences of four different lengths (1.3-2.2 kilobases), suggesting there are at least four transcribed loci. The number of nonsynonymous substitutions (d(N)) in the peptide binding region of exon 3 were higher than the number of synonymous substitutions (d(S)), indicating balancing selection in this region. The number of transcribed genes and the numerous RFLP fragments found so far suggest that the great reed warbler does not have a "minimal essential Mhc" as has been suggested for the chicken.
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| 6. |
- Wittzell, Håkan, et al.
(författare)
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Concerted evolution of two Mhc class II B loci in pheasants and domestic chickens
- 1999
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Ingår i: Molecular biology and evolution. - 0737-4038. ; 16:4, s. 479-490
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Tidskriftsartikel (refereegranskat)abstract
- The major histocompatibility complex (Mhc) of the ring-necked pheasant contains two polymorphic Mhc class II B genes. We show here, by screening of a cDNA library and RT-PCR from RNA, that both of these loci, Phco-DAB1 and Phco-DAB2, normally are transcribed in the spleen. They differ mainly in the 3' untranslated (UT) region, with the transcript lengths, not including the poly(A) tails, being 1,100 nt for DAB1 and 955 nt for DAB2. These two loci are orthologous to the B-LBI and B-LBII loci of the domestic chicken, respectively. DAB1 and DAB2 therefore seem to have evolved from a duplication before the split of the evolutionary lineages leading to the pheasant and the domestic chicken ca. 20 MYA. This is the first report of an orthologous relationship between avian Mhc genes. Yet, the third exons of DAB1 and DAB2 were identical in all available sequences and differed at 10 positions from the exon 3 sequences of B-LBI/B-LBII. The species-specific exon 3 suggests that DAB1 and DAB2 are subject to concerted evolution, i.e., interlocus genetic exchange. The exon 2 sequences show characteristic polymorphism, with hypervariable segments occurring in different combinations in different alleles. Given the divergence in the 3'UT region, the finding of the same exon 2 sequence at both the DAB1 and the DAB2 loci in one of the pheasant haplotypes also suggests that interlocus genetic exchange does occur. Accordingly, the exon 2 sequences tended to cluster irrespective of locus in the phylogenetic analyses. Genetic exchange simultaneously involving both exon 2 and exon 3 may be facilitated by the short length of the intervening intron (<100 bp) in pheasants and domestic chickens compared with, e.g., humans (about 3 kb).
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| 7. |
- Wittzell, Håkan, et al.
(författare)
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MHC variation in birds and reptiles
- 1998
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Ingår i: Genetica. - 1573-6857. ; 104:3, s. 301-309
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Tidskriftsartikel (refereegranskat)abstract
- The major histocompatibility complex (MHC) has been studied in a multitude of mammals by now, but much less is known about its organisation and variation in other vertebrate species. The mammalian MHC is organised as a single gene cluster, but recent studies on birds suggest that this paradigm of MHC organisation has to be supplemented. The domestic chicken thus possesses two separate gene clusters which both contain MHC class I and class II B genes, and we have shown that the ring-necked pheasant Phasianus colchicus also has two unlinked clusters of class II B genes. We are studying the effect of the MHC on mate choice, survival and reproductive success in natural populations of birds and reptiles. For this reason, we are developing DNA techniques to determine the animals' MHC genotype. The amplification of the hypervariable exon 3 of the class I gene from songbirds and reptiles has provided us with species specific probes that can be used in Southern blot analysis. The first results indicate very extensive variation in all studied species, that is starlings Sturnus vulgaris, great reed warblers Acrocephalus arundinaceus and water pythons Liasis fuscus. The restriction fragment length polymorphism (RFLP) analysis also suggests that the number of MHC genes is significantly larger in these species than in pheasants and domestic chickens.
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| 8. |
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