| 1. |
- Lindholm, Anna K., et al.
(författare)
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The Ecology and Evolutionary Dynamics of Meiotic Drive
- 2016
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Ingår i: Trends in Ecology & Evolution. - : Elsevier BV. - 0169-5347 .- 1872-8383. ; 31:4, s. 315-326
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Forskningsöversikt (refereegranskat)abstract
- Meiotic drivers are genetic variants that selfishly manipulate the production of gametes to increase their own rate of transmission, often to the detriment of the rest of the genome and the individual that carries them. This genomic conflict potentially occurs whenever a diploid organism produces a haploid stage, and can have profound evolutionary impacts on gametogenesis, fertility, individual behaviour, mating system, population survival, and reproductive isolation. Multiple research teams are developing artificial drive systems for pest control, utilising the transmission advantage of drive to alter or exterminate target species. Here, we review current knowledge of how natural drive systems function, how drivers spread through natural populations, and the factors that limit their invasion.
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| 2. |
- Abdo, A. A., et al.
(författare)
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Multi-wavelength observations of the flaring gamma-ray blazar 3C 66A in 2008 October
- 2011
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 726:1, s. 43-
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Tidskriftsartikel (refereegranskat)abstract
- The BL Lacertae object 3C 66A was detected in a flaring state by the Fermi Large Area Telescope (LAT) and VERITAS in 2008 October. In addition to these gamma-ray observations, F-GAMMA, GASP-WEBT, PAIRITEL, MDM, ATOM, Swift, and Chandra provided radio to X-ray coverage. The available light curves show variability and, in particular, correlated flares are observed in the optical and Fermi-LAT gamma-ray band. The resulting spectral energy distribution can be well fitted using standard leptonic models with and without an external radiation field for inverse Compton scattering. It is found, however, that only the model with an external radiation field can accommodate the intra-night variability observed at optical wavelengths.
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| 3. |
- Abeysekara, A. U., et al.
(författare)
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VERITAS and Fermi-LAT Observations of TeV Gamma-Ray Sources Discovered by HAWC in the 2HWC Catalog
- 2018
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Ingår i: Astrophysical Journal. - : Institute of Physics Publishing. - 0004-637X .- 1538-4357. ; 866:1
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Tidskriftsartikel (refereegranskat)abstract
- The High Altitude Water Cherenkov (HAWC) collaboration recently published their 2HWC catalog, listing 39 very high energy (VHE; >100 GeV) gamma-ray sources based on 507 days of observation. Among these, 19 sources are not associated with previously known teraelectronvolt (TeV) gamma-ray sources. We have studied 14 of these sources without known counterparts with VERITAS and Fermi-LAT. VERITAS detected weak gamma-ray emission in the 1 TeV-30 TeV band in the region of DA 495, a pulsar wind nebula coinciding with 2HWC J1953+294, confirming the discovery of the source by HAWC. We did not find any counterpart for the selected 14 new HAWC sources from our analysis of Fermi-LAT data for energies higher than 10 GeV. During the search, we detected gigaelectronvolt (GeV) gamma-ray emission coincident with a known TeV pulsar wind nebula, SNR G54.1+0.3 (VER J1930+188), and a 2HWC source, 2HWC J1930+188. The fluxes for isolated, steady sources in the 2HWC catalog are generally in good agreement with those measured by imaging atmospheric Cherenkov telescopes. However, the VERITAS fluxes for SNR G54.1+0.3, DA 495, and TeV J2032+4130 are lower than those measured by HAWC, and several new HAWC sources are not detected by VERITAS. This is likely due to a change in spectral shape, source extension, or the influence of diffuse emission in the source region.
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| 4. |
- Acciari, V. A., et al.
(författare)
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Discovery of very high energy gamma rays from PKS 1424+240 and multiwavelength constraints on ITS redshift
- 2010
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Ingår i: ASTROPHYSICAL JOURNAL LETTERS. - 2041-8205. ; 708:2, s. L100-L106
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Tidskriftsartikel (refereegranskat)abstract
- We report the first detection of very high energy(83) (VHE) gamma-ray emission above 140 GeV from PKS 1424+240, a BL Lac object with an unknown redshift. The photon spectrum above 140 GeV measured by VERITAS is well described by a power law with a photon index of 3.8 +/- 0.5(stat) +/- 0.3(syst) and a flux normalization at 200 GeV of (5.1 +/- 0.9(stat) +/- 0.5(syst)) x 10(-11) TeV-1 cm(-2) s(-1), where stat and syst denote the statistical and systematical uncertainties, respectively. The VHE flux is steady over the observation period between MJD 54881 and 55003 (from 2009 February 19 to June 21). Flux variability is also not observed in contemporaneous high-energy observations with the Fermi Large Area Telescope. Contemporaneous X-ray and optical data were also obtained from the Swift XRT and MDM observatory, respectively. The broadband spectral energy distribution is well described by a one-zone synchrotron self-Compton model favoring a redshift of less than 0.1. Using the photon index measured with Fermi in combination with recent extragalactic background light absorption models it can be concluded from the VERITAS data that the redshift of PKS 1424+240 is less than 0.66.
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| 5. |
- Acciari, V. A., et al.
(författare)
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THE DISCOVERY OF gamma-RAY EMISSION FROM THE BLAZAR RGB J0710+591
- 2010
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Ingår i: ASTROPHYSICAL JOURNAL LETTERS. - 2041-8205. ; 715:1, s. L49-L55
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Tidskriftsartikel (refereegranskat)abstract
- The high-frequency-peaked BL Lacertae object RGB J0710+591 was observed in the very high-energy (VHE; E > 100 GeV) wave band by the VERITAS array of atmospheric Cherenkov telescopes. The observations, taken between 2008 December and 2009 March and totaling 22.1 hr, yield the discovery of VHE gamma rays from the source. RGB J0710+591 is detected at a statistical significance of 5.5 standard deviations (5.5 sigma) above the background, corresponding to an integral flux of (3.9 +/- 0.8) x 10(-12) cm(-2) s(-1) (3% of the Crab Nebula's flux) above 300 GeV. The observed spectrum can be fit by a power law from 0.31 to 4.6 TeV with a photon spectral index of 2.69 +/- 0.26(stat) +/- 0.20(sys). These data are complemented by contemporaneous multiwavelength data from the Fermi Large Area Telescope, the Swift X-ray Telescope, the Swift Ultra-Violet and Optical Telescope, and the Michigan-Dartmouth-MIT observatory. Modeling the broadband spectral energy distribution (SED) with an equilibrium synchrotron self-Compton model yields a good statistical fit to the data. The addition of an external-Compton component to the model does not improve the fit nor brings the system closer to equipartition. The combined Fermi and VERITAS data constrain the properties of the high-energy emission component of the source over 4 orders of magnitude and give measurements of the rising and falling sections of the SED.
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| 6. |
- Ament-Velásquez, S. Lorena, Ph.D. 1988-, et al.
(författare)
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Allorecognition genes drive reproductive isolation in Podospora anserina
- 2022
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Ingår i: Nature Ecology & Evolution. - : Springer Nature. - 2397-334X. ; 6:7, s. 910-923
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Tidskriftsartikel (refereegranskat)abstract
- Allorecognition, the capacity to discriminate self from conspecific non-self, is a ubiquitous organismal feature typically governed by genes evolving under balancing selection. Here, we show that in the fungus Podospora anserina, allorecognition loci controlling vegetative incompatibility (het genes), define two reproductively isolated groups through pleiotropic effects on sexual compatibility. These two groups emerge from the antagonistic interactions of the unlinked loci het-r (encoding a NOD-like receptor) and het-v (encoding a methyltransferase and an MLKL/HeLo domain protein). Using a combination of genetic and ecological data, supported by simulations, we provide a concrete and molecularly defined example whereby the origin and coexistence of reproductively isolated groups in sympatry is driven by pleiotropic genes under balancing selection.
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| 7. |
- Ament-Velásquez, Sandra Lorena, M.Sc. 1988-
(författare)
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Drivers of evolutionary change in Podospora anserina
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Genomic diversity is shaped by a myriad of forces acting in different directions. Some genes work in concert with the interests of the organism, often shaped by natural selection, while others follow their own interests. The latter genes are considered “selfish”, behaving either neutrally to the host, or causing it harm. In this thesis, I focused on genes that have substantial fitness effects on the fungus Podospora anserina and relatives, but whose effects are very contrasting. In Papers I and II, I explored the evolution of a particular type of selfish genetic elements that cause meiotic drive. Meiotic drivers manipulate the outcome of meiosis to achieve overrepresentation in the progeny, thus increasing their likelihood of invading and propagating in a population. In P. anserina there are multiple meiotic drivers but their genetic basis was previously unknown. In Paper I, we demonstrated that drive is caused by members of the Spok gene family. We discovered two new Spok genes, Spok3 and Spok4, which locate in different chromosomes in different strains. In Paper II, we showed that Spok3 and Spok4 are found on a gigantic (up to 247 Kb long) variant of Enterprise, a Crypton-like transposable element. Enterprise likely mobilize through the action of a putative tyrosine-recombinase that we call Kirc. When carrying the Spoks, this element has double selfish properties: transposition and meiotic drive. In addition, we found that homologs of the Spoks (Paper I) and of Kirc (Paper II) are widespread in fungi but their phylogenies are discordant with that of the species, suggesting that they have undergone horizontal gene transfer. In Papers III and IV, I turned the focus into genes that have an adaptive function. In fungi, the het genes control conspecific self/non-self recognition. Such genes are expected to evolve under frequency-dependent balancing selection. In Paper III, we found evidence of balancing selection acting on some het genes across the P. anserina species complex. Unexpectedly, we also discovered that het genes of the HNWD gene family are duplicated in a transposon-like manner, broadening our understanding of their potential fitness effects. Finally, in Paper IV we show how het genes with pleiotropic effects on sexual recognition lead to the evolution of strong reproductive isolation, and hence speciation. Overall, the results of my thesis highlight the functional intersection between mobile selfish genetic elements and other genes, either selfish or adaptive, and their effects on genome architecture and population structure.
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| 8. |
- Ament-Velásquez, Sandra Lorena, Ph.D. 1988-, et al.
(författare)
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High-Quality Genome Assemblies of 4 Members of the Podospora anserina Species Complex
- 2024
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Ingår i: Genome Biology and Evolution. - : Oxford University Press. - 1759-6653. ; 16:3
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Tidskriftsartikel (refereegranskat)abstract
- The filamentous fungus Podospora anserina is a model organism used extensively in the study of molecular biology, senescence, prion biology, meiotic drive, mating-type chromosome evolution, and plant biomass degradation. It has recently been established that P. anserina is a member of a complex of 7 closely related species. In addition to P. anserina, high-quality genomic resources are available for 2 of these taxa. Here, we provide chromosome-level annotated assemblies of the 4 remaining species of the complex, as well as a comprehensive data set of annotated assemblies from a total of 28 Podospora genomes. We find that all 7 species have genomes of around 35 Mb arranged in 7 chromosomes that are mostly collinear and less than 2% divergent from each other at genic regions. We further attempt to resolve their phylogenetic relationships, finding significant levels of phylogenetic conflict as expected from a rapid and recent diversification.
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| 9. |
- Ament-Velásquez, Sandra Lorena, M.Sc. 1988-, et al.
(författare)
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The evolution of the allorecognition gene repertoire in the Podospora anserina species complex
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Across the Tree of Life, self/non-self recognition is typically achieved through highly polymorphic loci under balancing selection. In fungi, vegetative conspecific recognition, or allorecognition, is defined by the compatibility interactions between loci known as het genes. In this study we explore the evolution of the het genes in the model fungus Podospora anserina and its closest relatives (the Podospora anserina species complex). First, we used chromosome-level genome assemblies to resolve their phylogenetic relationships. We found that the species in the complex are well defined but diversified recently and rapidly, leading to high degrees of conflict at deep branches of the phylogeny. Unlike typical orthologous genes from the complex, some allorecognition genes (het-z and het-s) show trans-species polymorphism, a hallmark of long-term balancing selection. By contrast, the het genes belonging to the HNWD family exhibit a high turn-over, with losses and duplications happening often. In particular, the species P. pseudocomata has a considerable increase of HNWD genes. Unexpectedly, we show that the HNWD paralogs have clean defined boundaries flanked by a target site duplication (TSD), implicating a DNA transposon-like mechanism in the genesis of new duplicates. Overall, our data highlights the diversity of evolutionary histories behind individual self/non-self recognition genes at short evolutionary timescales.
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| 10. |
- Ament-Velásquez, Sandra Lorena, Ph.D. 1988-, et al.
(författare)
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The plot thickens : haploid and triploid-like thalli, hybridization, and biased mating type ratios in Letharia
- 2021
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Ingår i: Frontiers in Fungal Biology. - : Frontiers Media S.A.. - 2673-6128. ; 2
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Tidskriftsartikel (refereegranskat)abstract
- The study of the reproductive biology of lichen fungal symbionts has been traditionally challenging due to their complex lifestyles. Against the common belief of haploidy, a recent genomic study found a triploid-like signal in Letharia. Here, we infer the genome organization and reproduction in Letharia by analyzing genomic data from a pure culture and from thalli, and performing a PCR survey of the MAT locus in natural populations. We found that the read count variation in the four Letharia specimens, including the pure culture derived from a single sexual spore of L. lupina, is consistent with haploidy. By contrast, the L. lupina read counts from a thallus’ metagenome are triploid-like. Characterization of the mating-type locus revealed a conserved heterothallic configuration across the genus, along with auxiliary genes that we identified. We found that the mating-type distributions are balanced in North America for L. vulpina and L. lupina, suggesting widespread sexual reproduction, but highly skewed in Europe for L. vulpina, consistent with predominant asexuality. Taken together, we propose that Letharia fungi are heterothallic and typically haploid, and provide evidence that triploid-like individuals are hybrids between L. lupina and an unknown Letharia lineage, reconciling classic systematic and genetic studies with recent genomic observations.
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