| 1. |
- Hansson, Bengt, et al.
(författare)
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Contrasting results from GWAS and QTL mapping on wing length in great reed warblers
- 2018
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Ingår i: Molecular Ecology Resources. - : Wiley. - 1755-098X .- 1755-0998. ; 18:4, s. 867-876
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Tidskriftsartikel (refereegranskat)abstract
- A major goal in evolutionary biology is to understand the genetic basis of adaptive traits. In migratory birds, wing morphology is such a trait. Our previous work on the great reed warbler (Acrocephalus arundinaceus) shows that wing length is highly heritable and under sexually antagonistic selection. Moreover, a quantitative trait locus (QTL) mapping analysis detected a pronounced QTL for wing length on chromosome 2, suggesting that wing morphology is partly controlled by genes with large effects. Here, we re-evaluate the genetic basis of wing length in great reed warblers using a genomewide association study (GWAS) approach based on restriction site-associated DNA sequencing (RADseq) data. We use GWAS models that account for relatedness between individuals and include covariates (sex, age and tarsus length). The resulting association landscape was flat with no peaks on chromosome 2 or elsewhere, which is in line with expectations for polygenic traits. Analysis of the distribution of p-values did not reveal biases, and the inflation factor was low. Effect sizes were however not uniformly distributed on some chromosomes, and the Z chromosome had weaker associations than autosomes. The level of linkage disequilibrium (LD) in the population decayed to background levels within c. 1 kbp. There could be several reasons to why our QTL study and GWAS gave contrasting results including differences in how associations are modelled (cosegregation in pedigree vs. LD associations), how covariates are accounted for in the models, type of marker used (multi- vs. biallelic), difference in power or a combination of these. Our study highlights that the genetic architecture even of highly heritable traits is difficult to characterize in wild populations.
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| 2. |
- Ponnikas, Suvi, et al.
(författare)
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Turnover and post-bottleneck genetic structure in a recovering population of Peregrine Falcons Falco peregrinus
- 2017
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Ingår i: Ibis. - : Wiley. - 0019-1019. ; 159:2, s. 311-323
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Tidskriftsartikel (refereegranskat)abstract
- Dispersal is a process that increases genetic diversity and genetic connectivity of populations. We studied the turnover rate of breeding adults and genetic population structure to estimate dispersal in Peregrine Falcons in Finland. We used relatedness estimates among Finnish Peregrine Falcons over a 5-year period, genotyping over 500 nestlings with 10 microsatellite loci to reveal the rate of turnover. Our results reveal a high turnover rate (21.7%) that does not seem to be correlated with the breeding success of the previous year. The extent of population genetic structure and diversity, and possible signs of the population crash during the 1970s, was assessed with a reduced dataset, excluding relatives. We found genetic diversity to be similar to previously studied falcon populations (expected heterozygosity of 0.581) and no population genetic structuring among our sampled populations. We did not find a genetic imprint of the past population bottleneck that the Finnish Peregrine population experienced. We conclude that high dispersal rates are likely to have contributed to maintaining genetic diversity across the landscape, by mixing individuals within the species' distribution in Finland and thus preventing genetic structuring and negative effects associated with the population decline in the 1970s.
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| 3. |
- Ponnikas, Suvi, et al.
(författare)
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Why Do Sex Chromosomes Stop Recombining?
- 2018
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Ingår i: Trends in Genetics. - : Elsevier BV. - 0168-9525. ; 34:7, s. 492-503
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Tidskriftsartikel (refereegranskat)abstract
- It is commonly assumed that sex chromosomes evolve recombination suppression because selection favours linkage between sex-determining and sexually antagonistic genes. However, although the role of sexual antagonism during sex chromosome evolution has attained strong support from theory, experimental and observational evidence is rare or equivocal. Here, we highlight alternative, often neglected, hypotheses for recombination suppression on sex chromosomes, which invoke meiotic drive, heterozygote advantage, and genetic drift, respectively. We contrast the hypotheses, the situations when they are likely to be of importance, and outline why it is surprisingly difficult to test them. Lastly, we discuss future research directions (including modelling, population genomics, comparative approaches, and experiments) to disentangle the different hypotheses of sex chromosome evolution.
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| 4. |
- Sigeman, Hanna, et al.
(författare)
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Insights into avian incomplete dosage compensation : Sex-biased gene expression coevolves with sex chromosome degeneration in the common whitethroat
- 2018
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Ingår i: Genes. - : MDPI AG. - 2073-4425. ; 9:8
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Tidskriftsartikel (refereegranskat)abstract
- Non-recombining sex chromosomes (Y and W) accumulate deleterious mutations and degenerate. This poses a problem for the heterogametic sex (XY males; ZW females) because a single functional gene copy often implies less gene expression and a potential imbalance of crucial expression networks. Mammals counteract this by dosage compensation, resulting in equal sex chromosome expression in males and females, whereas birds show incomplete dosage compensation with significantly lower expression in females (ZW). Here, we study the evolution of Z and W sequence divergence and sex-specific gene expression in the common whitethroat (Sylvia communis), a species within the Sylvioidea clade where a neo-sex chromosome has been formed by a fusion between an autosome and the ancestral sex chromosome. In line with data from other birds, females had lower expression than males at the majority of sex-linked genes. Results from the neo-sex chromosome region showed thatWgametologs have diverged functionally to a higher extent than their Z counterparts, and that the female-to-male expression ratio correlated negatively with the degree of functional divergence of these gametologs. We find it most likely that sex-linked genes are being suppressed in females as a response to W chromosome degradation, rather than that these genes experience relaxed selection, and thus diverge more, by having low female expression. Overall, our data of this unique avian neo-sex chromosome system suggest that incomplete dosage compensation evolves, at least partly, through gradual accumulation of deleterious mutations at the W chromosome and declining female gene expression.
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| 5. |
- Sigeman, Hanna, et al.
(författare)
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Repeated sex chromosome evolution in vertebrates supported by expanded avian sex chromosomes
- 2019
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Ingår i: Royal Society of London. Proceedings B. Biological Sciences. - : The Royal Society. - 1471-2954. ; 286:1916
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Tidskriftsartikel (refereegranskat)abstract
- Sex chromosomes have evolved from the same autosomes multiple times across vertebrates, suggesting that selection for recombination suppression has acted repeatedly and independently on certain genetic backgrounds. Here, we perform comparative genomics of a bird clade (larks and their sister lineage; Alaudidae and Panuridae) where multiple autosome-sex chromosome fusions appear to have formed expanded sex chromosomes. We detected the largest known avian sex chromosome (195.3 Mbp) and show that it originates from fusions between parts of four avian chromosomes: Z, 3, 4A and 5. Within these four chromosomes, we found evidence of five evolutionary strata where recombination had been suppressed at different time points, and show that stratum age explained the divergence rate of Z-W gametologs. Next, we analysed chromosome content and found that chromosome 3 was significantly enriched for genes with predicted sex-related functions. Finally, we demonstrate extensive homology to sex chromosomes in other vertebrate lineages: chromosomes Z, 3, 4A and 5 have independently evolved into sex chromosomes in fish (Z), turtles (Z, 5), lizards (Z, 4A), mammals (Z, 4A) and frogs (Z, 3, 4A, 5). Our results provide insights into and support for repeated evolution of sex chromosomes in vertebrates.
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