| 1. |
- Christmas, Matthew J, et al.
(författare)
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Chromosomal inversions associated with environmental adaptation in honeybees
- 2019
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Ingår i: Molecular Ecology. - : WILEY. - 0962-1083 .- 1365-294X. ; 28:6, s. 1358-1374
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Tidskriftsartikel (refereegranskat)abstract
- Chromosomal inversions can facilitate local adaptation in the presence of gene flow by suppressing recombination between well-adapted native haplotypes and poorly adapted migrant haplotypes. East African mountain populations of the honeybee Apis mellifera are highly divergent from neighbouring lowland populations at two extended regions in the genome, despite high similarity in the rest of the genome, suggesting that these genomic regions harbour inversions governing local adaptation. Here, we utilize a new highly contiguous assembly of the honeybee genome to characterize these regions. Using whole-genome sequencing data from 55 highland and lowland bees, we find that the highland haplotypes at both regions are present at high frequencies in three independent highland populations but extremely rare elsewhere. The boundaries of both divergent regions are characterized by regions of high homology with each other positioned in opposite orientations and contain highly repetitive, long inverted repeats with homology to transposable elements. These regions are likely to represent inversion breakpoints that participate in nonallelic homologous recombination. Using long-read data, we confirm that the lowland samples are contiguous across breakpoint regions. We do not find evidence for disruption of functional sequence by these breakpoints, which suggests that the inversions are likely maintained due to their allelic content conferring local adaptation in highland environments. Finally, we identify a third divergent genomic region, which contains highly divergent segregating haplotypes that also may contain inversion variants under selection. The results add to a growing body of evidence indicating the importance of chromosomal inversions in local adaptation.
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| 2. |
- Christmas, Matthew, et al.
(författare)
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Social Parasitism in the Honeybee (Apis mellifera) Is Not Controlled by a Single SNP
- 2019
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Ingår i: Molecular biology and evolution. - : Oxford University Press (OUP). - 0737-4038 .- 1537-1719. ; 36:8, s. 1764-1767
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Tidskriftsartikel (refereegranskat)abstract
- The Cape bee (Apis mellifera capensis) is a subspecies of the honeybee, in which workers commonly lay diploid unfertilized eggs via a process known as thelytoky. A recent study aimed to map the genetic basis of this trait in the progeny of a single capensis queen where workers laid either diploid (thelytokous) or haploid (arrhenotokous) eggs. A nonsynonymous single nucleotide polymorphism (SNP) in a gene of unknown function was reported to be strongly associated with thelytoky in this colony. Here, we analyze genome sequences from a global sample of A. mellifera and identify populations where the proposed thelytoky allele at this SNP is common but thelytoky is absent. We also analyze genome sequences of three capensis queens produced by thelytoky and find that, contrary to predictions, they do not carry the proposed thelytoky allele. The proposed SNP is therefore neither sufficient nor required to produce thelytoky in A. mellifera.
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| 3. |
- Jones, Julia C., et al.
(författare)
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Extreme Differences in Recombination Rate between the Genomes of a Solitary and a Social Bee
- 2019
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Ingår i: Molecular biology and evolution. - : Oxford University Press (OUP). - 0737-4038 .- 1537-1719. ; 36:10, s. 2277-2291
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Tidskriftsartikel (refereegranskat)abstract
- Social insect genomes exhibit the highest rates of crossing over observed in plants and animals. The evolutionary causes of these extreme rates are unknown. Insight can be gained by comparing recombination rate variation across the genomes of related social and solitary insects. Here, we compare the genomic recombination landscape of the highly social honey bee, Apis mellifera, with the solitary alfalfa leafcutter bee, Megachile rotundata, by analyzing patterns of linkage disequilibrium in population-scale genome sequencing data. We infer that average recombination rates are extremely elevated in A. mellifera compared with M. rotundata. However, our results indicate that similar factors control the distribution of crossovers in the genomes of both species. Recombination rate is significantly reduced in coding regions in both species, with genes inferred to be germline methylated having particularly low rates. Genes with worker-biased patterns of expression in A. mellifera and their orthologs in M. rotundata have higher than average recombination rates in both species, suggesting that selection for higher diversity in genes involved in worker caste functions in social taxa is not the explanation for these elevated rates. Furthermore, we find no evidence that recombination has modulated the efficacy of selection among genes during bee evolution, which does not support the hypothesis that high recombination rates facilitated positive selection for new functions in social insects. Our results indicate that the evolution of sociality in insects likely entailed selection on modifiers that increased recombination rates genome wide, but that the genomic recombination landscape is determined by the same factors.
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| 4. |
- Montero-Mendieta, Santiago, et al.
(författare)
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The genomic basis of adaptation to high-altitude habitats in the eastern honey bee (Apis cerana)
- 2019
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Ingår i: Molecular Ecology. - : WILEY. - 0962-1083 .- 1365-294X. ; 28:4, s. 746-760
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Tidskriftsartikel (refereegranskat)abstract
- The eastern honey bee (Apis cerana) is of central importance for agriculture in Asia. It has adapted to a wide variety of environmental conditions across its native range in southern and eastern Asia, which includes high-altitude regions. eastern honey bees inhabiting mountains differ morphologically from neighbouring lowland populations and may also exhibit differences in physiology and behaviour. We compared the genomes of 60 eastern honey bees collected from high and low altitudes in Yunnan and Gansu provinces, China, to infer their evolutionary history and to identify candidate genes that may underlie adaptation to high altitude. Using a combination of F-ST-based statistics, long-range haplotype tests and population branch statistics, we identified several regions of the genome that appear to have been under positive selection. These candidate regions were strongly enriched for coding sequences and had high haplotype homozygosity and increased divergence specifically in highland bee populations, suggesting they have been subjected to recent selection in high-altitude habitats. Candidate loci in these genomic regions included genes related to reproduction and feeding behaviour in honey bees. Functional investigation of these candidate loci is necessary to fully understand the mechanisms of adaptation to high-altitude habitats in the eastern honey bee.
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| 5. |
- Baruch, Zdravko, et al.
(författare)
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Functional acclimation across microgeographic scales in Dodonaea viscosa
- 2018
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Ingår i: AoB Plants. - : Oxford University Press (OUP). - 2041-2851. ; 10:3
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Tidskriftsartikel (refereegranskat)abstract
- Intraspecific plant functional trait variation provides mechanistic insight into persistence and can infer population adaptive capacity. However, most studies explore intraspecific trait variation in systems where geographic and environmental distances co-vary. Such a design reduces the certainty of trait-environment associations, and it is imperative for studies that make trait-environment associations be conducted in systems where environmental distance varies independently of geographic distance. Here we explored trait variation in such a system, and aimed to: (i) quantify trait variation of parent and offspring generations, and associate this variation to parental environments; (ii) determine the traits which best explain population differences; (iii) compare parent and offspring trait-trait relationships. We characterized 15 plant functional traits in eight populations of a shrub with a maximum separation ca. 100 km. Populations differed markedly in aridity and elevation, and environmental distance varied independently of geographic distance. We measured traits in parent populations collected in the field, as well as their offspring reared in greenhouse conditions. Parent traits regularly associated with their environment. These associations were largely lost in the offspring generation, indicating considerable phenotypic plasticity. An ordination of parent traits showed clear structure with strong influence of leaf area, specific leaf area, stomatal traits, isotope delta C-13 and delta N-15 ratios, and N-area, whereas the offspring ordination was less structured. Parent trait-trait correlations were in line with expectations from the leaf economic spectrum. We show considerable trait plasticity in the woody shrub over microgeographic scales (<100 km), indicating it has the adaptive potential within a generation to functionally acclimate to a range of abiotic conditions. Since our study shrub is commonly used for restoration in southern Australia and local populations do not show strong genetic differentiation in functional traits, the potential risks of transferring seed across the broad environmental conditions are not likely to be a significant issue.
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| 6. |
- Christmas, Matthew, et al.
(författare)
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Measuring genome-wide genetic variation to reassess subspecies classifications in Dodonaea viscosa (Sapindaceae)
- 2018
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Ingår i: Australian Journal of Botany. - : CSIRO PUBLISHING. - 0067-1924 .- 1444-9862. ; 66:4, s. 287-297
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Tidskriftsartikel (refereegranskat)abstract
- Subspecies are traditionally defined on the basis of geographic discontinuities in phenotypic traits, and their circumscription is useful to distinguish morphologically differentiated populations. However, the robustness of morphology-based subspecies classifications in the genomics era is coming under increasing scrutiny, and phylogenies inferred from molecular data may not match with morphological approaches. The division of the shrub Dodonaea viscosa into seven subspecies within Australia has been based mainly on variation in leaf shape, which is a notably variable phenotypic character in this species. So as to assess the alignment between genetic variation and subspecies assignment, we genotyped 67 D. viscosa plants, including representatives from each of the seven subspecies, for 941 single nucleotide polymorphisms. Weused network-and Bayesian-based methods to assess genetic relatedness between sampled individuals. Structure analysis identified two genetic clusters, with a further substructure being identified within one of the clusters. Genetic clusters partially aligned with subspecies classifications, particularly for the three most morphologically distinct subspecies (ssp. mucronata, ssp. viscosa and ssp. burmanniana). Subspecies inhabiting the arid zone (ssp. mucronata and ssp. angustissima) exhibited the most distinct genetic clustering. For subspecies inhabiting more temperate regions of its range (ssp. angustifolia, ssp. cuneata and ssp. spatulata), genetic groups did not correspond well with subspecies classifications, but rather were better explained by the geographic origin of individuals. We suggest that the current subspecific classification of the hopbush does not accurately reflect the evolutionary history of this species, and recommend that phenotypic variation be reassessed in light of the genetic structure we describe here. The roles of environmental change, selection and geographic isolation are discussed in an attempt to explain the contemporary distribution of genetic variation in D. viscosa in Australia.
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| 7. |
- Kireta, Dona, et al.
(författare)
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Disentangling the evolutionary history of three related shrub species using genome-wide molecular markers
- 2019
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Ingår i: Conservation Genetics. - : Springer Science and Business Media LLC. - 1566-0621 .- 1572-9737. ; 20:5, s. 1101-1112
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Tidskriftsartikel (refereegranskat)abstract
- Understanding population genetic structure provides insight into historic population connectivity, and is largely driven by migration, population size, and species life history. During the last glacial maximum, sea levels around the biogeographically interesting, but poorly studied, South Australian coastal plains and geosyncline were thought to be sufficiently low that three prominent peninsulas (Fleurieu, Yorke, Eyre) and a large offshore island (Kangaroo Island) formed a continuous landmass. However, the degree to which population genetic structure in this region has been shaped by biogeography remains largely untested. Here, we use genome-wide SNP data from three Goodenia shrub species with contrasting growth forms to assess how historical and contemporary processes have shaped population genetic structure. These species occur commonly throughout South Australia and are used extensively in revegetation. The two woody species (Goodenia varia, G. ovata) displayed low genetic differentiation across the southern parts of the peninsulas and island, reflecting historical landscape connectivity. The third more-herbaceous species (G. amplexans) displayed higher genetic structure across the land features, reflecting contemporary disconnectivity. Kangaroo Island and the southern Flinders Ranges had relatively high genetic diversity, providing further evidence that they were important putative Pleistocene refugia. We demonstrate that historic changes in landscape and possible migration to and from refugia, have shaped the population genetic structure in these closely related shrubs, which may have been influenced by contemporary factors and small population sizes. We highlight the importance of using multi-species designs when studying historical population connectivity in understudied regions of the world.
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