163 research outputs found
Populationsgenetisk kartlÀggning av VÀnerlax
I VÀnern finns tvÄ av vÀrldens fÄ kvarvarande bestÄnd av storvuxen insjölevande Atlantisk lax samt ett antal storvuxna öringstammar. Sedan 1800-talet har omfattande exploatering av lek- och uppvÀxtomrÄden i tillrinnande vattendrag kraftigt försÀmrat laxfiskens naturliga förutsÀttningar, och en majoritet av VÀnernomrÄdets ursprungliga laxfiskstammar Àr idag utdöda. För att kompensera produktionsbortfall orsakade av vattenkraftens utbyggnad pÄgÄr sedan lÀnge omfattande odlings- och utsÀttningsverksamhet baserad pÄ lax och öring med ursprung frÄn KlarÀlven och GullspÄngsÀlven. I dessa vattendrag förekommer Àven vild produktion av lax, och dÀr finns ocksÄ de idag viktigaste uppvÀxtomrÄdena för sjövandrande vildfödd öring.
KlarĂ€lvens och GullspĂ„ngsĂ€lvens lax- och öringstammar anses ha högt bevarandevĂ€rde. De utgör samtidigt vĂ€rdefulla biologiska resurser för fisket. LĂ„ngvarigt svaga vilda bestĂ„nd, en odlingsverksamhet som lĂ€nge baserade sig pĂ„ ett lĂ„gt antal avelsfiskar, förekomst av stamkorsningar samt genutbyte mellan odlad och vild fisk förvĂ€ntas ha förĂ€ndrat stammarnas genetiska sammansĂ€ttning. Hittills har det emellertid varit oklart hur stora förĂ€ndringar som Ă€gt rum och hur âgenetiskt ursprungligaâ dagens stammar Ă€r. I denna rapport presenteras en omfattande genetisk kartlĂ€ggning av vild och odlad lax och öring av GullspĂ„ngs- respektive KlarĂ€lvsstam. Genom att jĂ€mföra genetisk information (mikrosatellit-DNA) som extraherats frĂ„n fjĂ€llprover insamlade under tidigare decennier med nutida material har det varit möjligt att analysera hur stammarna förĂ€ndrats. Samma information har Ă€ven anvĂ€nts för att skatta stammarnas genetiskt effektiva populationsstorlekar samt graden av genflöde och genetisk stamblandning (hybridisering).
Resultaten visar att GullspĂ„ngsĂ€lvens och KlarĂ€lvens lax- och öringstammar har förĂ€ndrats sedan 1960-talet tack vare en kombination av genflöde och slumpmĂ€ssiga genetiska förĂ€ndringar orsakade av fĂ„ förĂ€ldrafiskar (s.k. genetisk drift). Trots att förĂ€ndringarna i flera fall har varit pĂ„tagliga Ă„terstĂ„r Ă€nnu tydliga stamskillnader, och det Ă€r sĂ„ledes befogat att Ă€ven fortsĂ€ttningsvis betrakta VĂ€nerstammarna som genetiskt unika och skyddsvĂ€rda. Resultaten Ă€r samtidigt mycket bekymmersamma. Exempelvis har andelen âursprungliga generâ hos dagens GullspĂ„ngslax skattats till endast ca 70 %, vilket motsvarar ett tillskott av omkring 6â9 % âKlarĂ€lvsgenerâ per generation sedan 1960-talet â en mycket hög nivĂ„. Avslutningsvis ges ett antal rekommendationer som syftar till att skydda och bevara VĂ€nerstammarnas genetiska status mer effektivt Ă€n hittills. Ett framgĂ„ngsrikt framtida bevarandearbete utgör en nödvĂ€ndighet för den vilda och odlade laxens och öringens lĂ„ngsiktiga produktionsförmĂ„ga och fortlevnad, och Ă€r dĂ€rigenom Ă€ven en grundförutsĂ€ttning för ett lĂ„ngsiktligt hĂ„llbart laxfiske i VĂ€nern
trans-Dichloridobis[dicycloÂhexÂyl(4-isopropylÂphenÂyl)phosphane-ÎșP]platinum(II) acetone monosolvate
The title compound, [PtCl2(C21H33P)2]·C3H6O, crystallizes with an accompanying acetone solvent molÂecule. The metal atom shows a distorted square-planar coordination environment, with a PâPtâP angle of 172.41â
(3)° as the most prominent feature. Both isopropyl fragments were treated as disordered over two conformations with occupancy ratios of 0.55â
(2):0.45â
(2) and 0.58â
(2):0.42â
(2). The solvent molÂecule was also disordered over two orientations in a 1:1 ratio. The crystal studied was a non-merohedral twin with a twin component of 32.4%
Resolution of the type material of the Asian elephant, Elephas maximus Linnaeus, 1758 (Proboscidea, Elephantidae)
The understanding of Earthâs biodiversity depends critically on the accurate identification and nomenclature of
species. Many species were described centuries ago, and in a surprising number of cases their nomenclature or type
material remain unclear or inconsistent. A prime example is provided by Elephas maximus, one of the most iconic
and well-known mammalian species, described and named by Linnaeus (1758) and today designating the Asian
elephant. We used morphological, ancient DNA (aDNA), and high-throughput ancient proteomic analyses to
demonstrate that a widely discussed syntype specimen of E. maximus, a complete foetus preserved in ethanol, is
actually an African elephant, genus Loxodonta. We further discovered that an additional E. maximus syntype,
mentioned in a description by John Ray (1693) cited by Linnaeus, has been preserved as an almost complete skeleton
at the Natural History Museum of the University of Florence. Having confirmed its identity as an Asian elephant
through both morphological and ancient DNA analyses, we designate this specimen as the lectotype of E. maximus
Itinerant Electron Ferromagnetism in the Quantum Hall Regime
We report on a study of the temperature and Zeeman-coupling-strength
dependence of the one-particle Green's function of a two-dimensional (2D)
electron gas at Landau level filling factor where the ground state is
a strong ferromagnet. Our work places emphasis on the role played by the
itinerancy of the electrons, which carry the spin magnetization and on
analogies between this system and conventional itinerant electron ferromagnets.
We discuss the application to this system of the self-consistent Hartree-Fock
approximation, which is analogous to the band theory description of metallic
ferromagnetism and fails badly at finite temperatures because it does not
account for spin-wave excitations. We go beyond this level by evaluating the
one-particle Green's function using a self-energy, which accounts for
quasiparticle spin-wave interactions. We report results for the temperature
dependence of the spin magnetization, the nuclear spin relaxation rate, and
2D-2D tunneling conductances. Our calculations predict a sharp peak in the
tunneling conductance at large bias voltages with strength proportional to
temperature. We compare with experiment, where available, and with predictions
based on numerical exact diagonalization and other theoretical approaches.Comment: 29 pages, 20 figure
Understanding the genetic complexity of puberty timing across the allele frequency spectrum
Pubertal timing varies considerably and is associated with later health outcomes. We performed multi-ancestry genetic analyses on ~800,000 women, identifying 1,080 signals for age at menarche. Collectively, these explained 11% of trait variance in an independent sample. Women at the top and bottom 1% of polygenic risk exhibited ~11 and ~14-fold higher risks of delayed and precocious puberty, respectively. We identified several genes harboring rare loss-of-function variants in ~200,000 women, including variants in ZNF483, which abolished the impact of polygenic risk. Variant-to-gene mapping approaches and mouse gonadotropin-releasing hormone neuron RNA sequencing implicated 665 genes, including an uncharacterized G-protein-coupled receptor, GPR83, which amplified the signaling of MC3R, a key nutritional sensor. Shared signals with menopause timing at genes involved in DNA damage response suggest that the ovarian reserve might signal centrally to trigger puberty. We also highlight body size-dependent and independent mechanisms that potentially link reproductive timing to later life disease
Search for dark matter produced in association with bottom or top quarks in âs = 13 TeV pp collisions with the ATLAS detector
A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fbâ1 of protonâproton collision data recorded by the ATLAS experiment at âs = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements
- âŠ