402 research outputs found
Sediment core fossils in ancient Lake Ohrid: testing for faunal change since the Last Interglacial
Ancient Lake Ohrid is probably of early Pleistocene or Pliocene origin and amongst the few lakes in the world harbouring an outstanding degree of endemic biodiversity. Although there is a long history of evolutionary research in Lake Ohrid, particularly on molluscs, a mollusc fossil record has been missing up to date. For the first time, gastropod and bivalve fossils are reported from the basal, calcareous part of a 2.6 m long sediment succession (core Co1200) from the north-eastern part of Lake Ohrid. Electron spin resonance (ESR) dating of mollusc shells from the same stratigraphic level yielded an age of 130 ± 28 ka. Lithofacies III sediments, i.e. a stratigraphic subdivision comprising the basal succession of core Co1200 between 181.5–263 cm, appeared solid, greyish-white, and consisted almost entirely of silt-sized endogenic calcite (CaCO<sub>3</sub>>70%) and intact and broken mollusc shells. Here we compare the faunal composition of the thanatocoenosis with recent mollusc associations in Lake Ohrid. A total of 13 mollusc species (9 gastropod and 4 bivalve species) could be identified within Lithofacies III sediments. The value of sediment core fossils for reconstructing palaeoenvironmental settings was evaluated and the agreement between sediment and palaeontological proxies was tested. <br><br> The study also aims at investigating major faunal changes since the Last Interglacial and searching for signs of extinction events. <br><br> The combined findings of the ecological study and the sediment characteristics suggest deposition in a shallow water environment during the Last Interglacial. The fossil fauna exclusively included species also found in the present fauna, i.e. no extinction events are evident for this site since the Last Interglacial. The thanatocoenosis showed the highest similarity with recent Intermediate Layer (5–25 m water depth) mollusc assemblages. The demonstrated existence of a mollusc fossil record in Lake Ohrid sediment cores also has great significance for future deep drilling projects. It can be hoped that a more far reaching mollusc fossil record will then be obtained, enabling insight into the early evolutionary history of Lake Ohrid
Investigating geographic and temporal genetic variation in the black grouse (Lyrurus tetrix) in the Italian Alps
The black grouse (Lyrurus tetrix) is a Galliform distributed across northern Eurasia, and is a game bird in
most EU countries. Although the species is listed as ‘Least Concern’ by the IUCN, populations at the
western and southern edges of its range are considered ‘Vulnerable’ due to increasing habitat
fragmentation and human disturbance. Between 1995 and 2017, in collaboration with several hunting
associations, we collected more than 600 black grouse samples across seven regions of the Italian Alps.
Ten microsatellite markers (STRs) and 2442 Single Nucleotide Polymorphisms (SNPs) were analysed in
large subsets of the collected data, with the aim of identifying environmental, temporal and anthropic
factors that affect the distribution and level of genomic variation. The main factor shaping the genetic
distances between populations based on STRs is the geographic distance between them (i.e. isolation-bydistance), but even the populations on the two extremes of our sampling area are very similar (Fst between
the two regions = 0.053). SNP data supports the STR analysis. However, isolation-by-resistance methods
for the larger STR data set show that both higher altitudes and urban areas inhibit movement of grouse
between populations. While temporal analysis of STRs for the Trentino-Alto Adige region showed no
significant change in the mean number of alleles and allelic size range between the two time frames
studied (e.g. mean number of alleles 1995-1999: 8.8, 2009-2010: 8.2), and the expected heterozygosity
was high in both time frames (1995-1999: 0.740, 2009-2010: 0.722). While black grouse population size
is reportedly decreasing, our results suggest there is no measurable genetic impact from this trend. Hence
this dataset provides a basis for future monitoring of genetic diversity in this charismatic alpine species
Experimental determination of the complete spin structure for anti-proton + proton -> anti-\Lambda + \Lambda at anti-proton beam momentum of 1.637 GeV/c
The reaction anti-proton + proton -> anti-\Lambda + \Lambda -> anti-proton +
\pi^+ + proton + \pi^- has been measured with high statistics at anti-proton
beam momentum of 1.637 GeV/c. The use of a transversely-polarized frozen-spin
target combined with the self-analyzing property of \Lambda/anti-\Lambda decay
allows access to unprecedented information on the spin structure of the
interaction. The most general spin-scattering matrix can be written in terms of
eleven real parameters for each bin of scattering angle, each of these
parameters is determined with reasonable precision. From these results all
conceivable spin-correlations are determined with inherent self-consistency.
Good agreement is found with the few previously existing measurements of spin
observables in anti-proton + proton -> anti-\Lambda + \Lambda near this energy.
Existing theoretical models do not give good predictions for those
spin-observables that had not been previously measured.Comment: To be published in Phys. Rev. C. Tables of results (i.e. Ref. 24) are
available at http://www-meg.phys.cmu.edu/~bquinn/ps185_pub/results.tab 24
pages, 16 figure
Single-Pion Production in pp Collisions at 0.95 GeV/c (II)
The single-pion production reactions , and
were measured at a beam momentum of 0.95 GeV/c (
400 MeV) using the short version of the COSY-TOF spectrometer. The central
calorimeter provided particle identification, energy determination and neutron
detection in addition to time-of-flight and angle measurements from other
detector parts. Thus all pion production channels were recorded with 1-4
overconstraints. Main emphasis is put on the presentation and discussion of the
channel, since the results on the other channels have already been
published previously. The total and differential cross sections obtained are
compared to theoretical calculations. In contrast to the channel we
find in the channel a strong influence of the excitation
already at this energy close to threshold. In particular we find a dependence in the pion angular distribution, typical for a
pure s-channel excitation and identical to that observed in the
channel. Since the latter is understood by a s-channel resonance in
the partial wave, we discuss an analogous scenario for the
channel
Measurement of Spin Transfer Observables in Antiproton-Proton -> Antilambda-Lambda at 1.637 GeV/c
Spin transfer observables for the strangeness-production reaction
Antiproton-Proton -> Antilambda-Lambda have been measured by the PS185
collaboration using a transversely-polarized frozen-spin target with an
antiproton beam momentum of 1.637 GeV/c at the Low Energy Antiproton Ring at
CERN. This measurement investigates observables for which current models of the
reaction near threshold make significantly differing predictions. Those models
are in good agreement with existing measurements performed with unpolarized
particles in the initial state. Theoretical attention has focused on the fact
that these models produce conflicting predictions for the spin-transfer
observables D_{nn} and K_{nn}, which are measurable only with polarized target
or beam. Results presented here for D_{nn} and K_{nn} are found to be in
disagreement with predictions from existing models. These results also
underscore the importance of singlet-state production at backward angles, while
current models predict complete or near-complete triplet-state dominance.Comment: 5 pages, 3 figure
On the Production of Pairs in pp Collisions at 0.8 GeV
Data accumulated recently for the exclusive measurement of the reaction at a beam energy of 0.793 GeV using the COSY-TOF
spectrometer have been analyzed with respect to possible events from the reaction channel. The latter is expected to be the only
production channel, which contains no major contributions from
resonance excitation close to threshold and hence should be a good testing
ground for chiral dynamics in the production process. No single event
has been found, which meets all conditions for being a candidate for the reaction. This gives an upper limit for the cross section of
0.16 b (90% C.L.), which is more than an order of magnitude smaller than
the cross sections of the other two-pion production channels at the same
incident energy
Drivers of phytoplankton community structure change with ecosystem ontogeny during the Quaternary
Freshwater species are particularly sensitive to climate fluctuations, but little is known of their response to the large-scale environmental change that took place during the Quaternary. This is partly due to the scarcity of continuously preserved freshwater sedimentary records with orbital chronology. We use a 1.363 Ma high-resolution fossil record of planktonic diatoms from ancient Lake Ohrid to evaluate the role of global and regional versus local-scale environmental change in driving temporal community dynamics. By using a Bayesian joint species distribution model, we found that communities were mostly driven by the local-scale environment. Its effects decreased over time, becoming less important than global and regional environment at the onset of the penultimate glacial, 0.183 Ma. Global and regional control over the environment became important with successive deepening of the lake at around 1.0 Ma, and its influence remained persistent until the present. Our high-resolution data demonstrate the critical role of lake depth and its thermal dynamics in determining phytoplankton response to environmental change by influencing lake mixing, nutrient and light availability. With this study we demonstrate the relative impact of various environmental factors and their scale dependant effect on the phytoplankton communities during the Quaternary, emphasizing the importance of not only considering climate fluctuations in driving their structure and temporal dynamics but also the local environment. (c) 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
The evolution of transmission mode
This article reviews research on the evolutionary mechanisms leading to different transmission modes. Such modes are often under genetic control of the host or the pathogen, and often in conflict with each other via trade-offs. Transmission modes may vary among pathogen strains and among host populations. Evolutionary changes in transmission mode have been inferred through experimental and phylogenetic studies, including changes in transmission associated with host-shifts and with evolution of the unusually complex life cycles of many parasites. Understanding the forces that determine the evolution of particular transmission modes presents a fascinating medley of problems for which there is a lack of good data and often a lack of conceptual understanding or appropriate methodologies. Our best information comes from studies that have been focused on the vertical vs. horizontal transmission dichotomy. With other kinds of transitions, theoretical approaches combining epidemiology and population genetics are providing guidelines for determining when and how rapidly new transmission modes may evolve, but these are still in need of empirical investigation and application to particular cases. Obtaining such knowledge is a matter of urgency in relation to extant disease threats
High-statistics measurements of the p̅p→Λ̅Λ and p̅p→Λ̅Σ0+c.c. reactions at threshold
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