| 1. |
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| 2. |
- Burri, Reto, et al.
(författare)
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Linked selection and recombination rate variation drive the evolution of the genomic landscape of differentiation across the speciation continuum of Ficedula flycatchers
- 2015
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Ingår i: Genome Research. - : Cold Spring Harbor Laboratory. - 1088-9051 .- 1549-5469. ; 25:11, s. 1656-1665
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Tidskriftsartikel (refereegranskat)abstract
- Speciation is a continuous process during which genetic changes gradually accumulate in the genomes of diverging species. Recent studies have documented highly heterogeneous differentiation landscapes, with distinct regions of elevated differentiation ("differentiation islands") widespread across genomes. However, it remains unclear which processes drive the evolution of differentiation islands; how the differentiation landscape evolves as speciation advances; and ultimately, how differentiation islands are related to speciation. Here, we addressed these questions based on population genetic analyses of 200 resequenced genomes from 10 populations of four Ficedula flycatcher sister species. We show that a heterogeneous differentiation landscape starts emerging among populations within species, and differentiation islands evolve recurrently in the very same genomic regions among independent lineages. Contrary to expectations from models that interpret differentiation islands as genomic regions involved in reproductive isolation that are shielded from gene flow, patterns of sequence divergence (d(XY) relative node depth) do not support a major role of gene flow in the evolution of the differentiation landscape in these species. Instead, as predicted by models of linked selection, genome-wide variation in diversity and differentiation can be explained by variation in recombination rate and the density of targets for selection. We thus conclude that the heterogeneous landscape of differentiation in Ficedula flycatchers evolves mainly as the result of background selection and selective sweeps in genomic regions of low recombination. Our results emphasize the necessity of incorporating linked selection as a null model to identify genome regions involved in adaptation and speciation.
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| 3. |
- Ekblom, Robert, et al.
(författare)
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Balancing selection, sexual selection and geographic structure in MHC genes of Great Snipe
- 2010
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Ingår i: Genetica. - : Springer Science and Business Media LLC. - 0016-6707 .- 1573-6857. ; 138:4, s. 453-461
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Tidskriftsartikel (refereegranskat)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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| 4. |
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| 5. |
- Ekblom, Robert, et al.
(författare)
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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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Ingår i: Molecular Ecology. - 0962-1083 .- 1365-294X. ; 13:12, s. 3821-3828
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Spatial pattern of MHC class II variation in the great snipe (Gallinago media)
- 2007
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Ingår i: Molecular Ecology. - 0962-1083 .- 1365-294X. ; 16:7, s. 1439-1451
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Hoglund, Jacob, et al.
(författare)
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A hybrid snipe Gallinago gallinago x G-media found in the wild
- 2015
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Ingår i: Journal of Ornithology = Journal fur Ornithologie. - : Springer Science and Business Media LLC. - 0021-8375 .- 1439-0361. ; 156:3, s. 819-827
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Tidskriftsartikel (refereegranskat)abstract
- A hybrid snipe male was observed and caught in 2009 in the Norwegian mountains. We report behaviour, vocalizations, morphology, and genetic data for this bird. Mitochondrial and nuclear DNA sequences revealed that the hybrid had a great snipe mother and a common snipe father. The hybrid was intermediate in most measured morphometric traits and showed some intermediate plumage characteristics. The behaviour was similar to that of a great snipe-it displayed and vocalised at a great snipe lek for more than a week. The song was somewhat reminiscent of a great snipe's, but lacked the frequency-modulated whistles that are part of the great snipe song, consisting of more rapid click notes of a narrower frequency spectrum. This is the only putative hybrid that we have found among the more than 4,400 adult individuals we have examined between 1986 and 2014 at great snipe leks in Norway, Sweden, Poland, and Estonia. Common snipes invariably occur near these sites. Reports on putative hybrids among snipe species are very rare, and we question the validity of previous claims. This is the first where the parental origins-and, indeed, the hybrid status-have been unequivocally determined. We speculate on how a great snipe female, known for being extremely choosy about mating, came to mate with a common snipe male. We also note that, although perhaps behaviourally more likely, physical constraints on chick development (caused by the smaller egg size of the common snipe and larger body size of the great snipe) might prevent any successful male great snipe x female common snipe hybridisation-a possible example of an unidirectional post-zygotic barrier.
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| 8. |
- Höglund, Jacob, et al.
(författare)
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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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Ingår i: Molecular Ecology. - : Wiley. - 0962-1083 .- 1365-294X. ; 26:13, s. 3458-3471
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Tidskriftsartikel (refereegranskat)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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| 9. |
- Kölzsch, Andrea, et al.
(författare)
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Population fluctuations and regulation in great snipe : a time-series analysis
- 2007
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Ingår i: Journal of Animal Ecology. - : Wiley. - 0021-8790 .- 1365-2656. ; 76:4, s. 740-749
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Tidskriftsartikel (refereegranskat)abstract
- 1. During the last centuries, the breeding range of the great snipe Gallinago media has declined dramatically in the western part of its distribution. To examine present population dynamics in the Scandinavian mountains, we collected and analysed a 19-year time series of counts of great snipe males at leks in central Norway, 1987-2005. 2. The population showed large annual fluctuations in the number of males displaying at lek sites (range 45-90 males at the peak of the mating season), but no overall trend. 3. We detected presence of direct density-dependent mechanisms regulating this population. Inclusion of the density-dependent term in a Ricker-type model significantly improved the fit with observed data (evaluated with Parametric Bootstrap Likelihood Ratio tests and Akaike's Information Criterion for small sample size). 4. An analysis of (a number of a priori likely) environmental covariates suggests that the population dynamics were affected by conditions influencing reproduction and survival of offspring during the summer, but not by conditions influencing survival at the wintering grounds in Africa. This is in contrast to many altricial birds breeding in the northern hemisphere, and supports the idea that population dynamics of migratory nidifugous birds are more influenced by conditions during reproduction. 5. Inclusion of these external factors into our model improved the detectability of density dependence. This illustrates that allowing for external effects may increase statistical power of density dependence tests and thus be of particular importance in relatively short time series. 6. In our best model of the population dynamics, two likely density-independent offspring survival covariates explained 47·3% of the variance in great snipe numbers (predation pressure estimated by willow grouse reproductive success and food availability estimated by the amount of precipitation in June), whereas density dependence explained 35·5%. Demographic stochasticity and unidentified environmental stochasticity may account for the remaining 17·2%.
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| 10. |
- Qvarnström, Anna, et al.
(författare)
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Song similarity predicts hybridization in flycatchers
- 2006
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Ingår i: Journal of Evolutionary Biology. - : Wiley. - 1010-061X .- 1420-9101. ; 19:4, s. 1202-1209
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Tidskriftsartikel (refereegranskat)abstract
- Given that population divergence in sexual signals is an important prerequisite for reproductive isolation, a key prediction is that cases of signal convergence should lead to hybridization. However, empirical studies that quantitatively demonstrate links between phenotypic characters of individuals and their likelihood to hybridize are rare. Here we show that song convergence between sympatric pied (Ficedula hypoleuca) and collared flycatchers (F. albicollis) influence social and sexual interactions between the two species. In sympatry, the majority of male pied flycatchers (65%) include various parts of collared flycatcher song in their song repertoire (but not vice versa). Playback experiments on male interactions demonstrate that male collared flycatchers respond similarly to this 'mixed' song as to conspecific song. Long-term data on pairing patterns show that males singing a converged song attract females of the other species: female collared flycatchers only pair with male pied flycatchers if the males sing the mixed song type. From the perspective of a male pied flycatcher, singing a mixed song type is associated with 30% likelihood of hybridization. This result, combined with our estimates of the frequency of mixed singers, accurately predicts the observed occurrence of hybridization among male pied flycatchers in our study populations (20.45% of 484 pairs; predicted 19.5%). Our results support the suggestion that song functions as the most important prezygotic isolation mechanism in many birds.
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