Rise and Fall of the Beringian Steppe Bison

The widespread extinctions of large mammals at the end of the Pleistocene epoch have often been attributed to the depredations of humans; here we present genetic evidence that questions this assumption. We used ancient DNA and Bayesian techniques to reconstruct a detailed genetic history of bison throughout the late Pleistocene and Holocene epochs. Our analyses depict a large diverse population living throughout Beringia until around 37,000 years before the present, when the population’s genetic diversity began to decline dramatically. The timing of this decline correlates with environmental changes associated with the onset of the last glacial cycle, whereas archaeological evidence does not support the presence of large populations of humans in Eastern Beringia until more than 15,000 years later.   Article Summary by Jonathan C. Driver, May 2015   This article explores the movement of North American bison and the special significance of Tse’K’wa in this research, shedding insight into how the first Paleoindian peoples of Canada arrived at the land. One of the fascinating aspects about archaeology today is the speed with which new scientific techniques are developed and applied to archaeological materials. This paper demonstrates why it is so important to keep material safely stored after it has been excavated – because you never know when it will be valuable to a future researcher or when it can yield new information about the past.   Quite a few years after the excavations at Tse’K’wa were finished I was approached by Alan Cooper and Beth Shapiro of Oxford University about the possibility of sampling early bison bones from the site, to see if they still had DNA preserved. Beth was writing her doctoral thesis on the evolution of bison, and she was being supervised by Alan, a highly accomplished researcher into ancient DNA. It turned out that the Tse’K’wa bison were well preserved, and Beth was able to extract DNA and include it in the study of hundreds of samples from North America and Asia. As an added bonus, Beth and Alan arranged for radiocarbon dates to be run on every bone they studied.This added to our understanding of the age of the site\u27s earliest material.   Beth summarized her doctoral research in this paper, published in the very prestigious journal “Science”. The many contributors to her research were listed as co-authors, recognizing that each of us had contributed in a small way to the research, by sharing samples and ideas.  While the paper mainly deals with Beth’s conclusions about the evolutionary history of bison, for those interested in Tse’K’wa and the history of the early peoples of Canada, there was a fascinating tidbit of information contained in the Tse’K’wa bison DNA – they were from two quite distinct populations.   To understand the significance of this, we must first consider the impact of the extensive ice sheets that formed across Canada about 20,000 years ago. The ice sheets separated North American bison into two populations. One group of bison herds lived to the south of the ice sheets, in what is today, the continental USA and very southern parts of Saskatchewan, Alberta and B.C. The other population lived in unglaciated regions of, what is today, Yukon, Alaska and northeast Asia. These two populations can be distinguished by minor differences in their DNA. When Beth studied the bison fossils from across the vast region of their ice-age distribution she found that in every location except one the bison were either northern or southern types. The one exception was Tse’K’wa where bison from both the north and south were found.   The explanation for this seems fairly straightforward. When the western Canadian ice sheets melted and new pastures were developed, northern bison began to move south through the Yukon and into northern and central BC and Alberta. At the same time, the southern bison began to move north, also following pastures that developed on the recently de-glaciated  landcapes.  Finally, the northern and southern populations met in the Peace River region. There is no evidence that they bred with each other, and, based on the genetics of modern bison in North America it appears that the southern form survived and evolved into the bison we are familiar with today.   The Tse’K’wa data suggest the meeting of bison populations must have occurred around the same time the site was first occupied by humans, as it is very unlikely that two genetically distinct populations of bison could have lived in the same environment without interbreeding or one of them becoming extinct. This means the establishment of a viable migration route for animals (and people) from Alaska through Yukon, B.C., Alberta and into continental USA must have happened after the dates of the earliest human presence in the continental USA and South America. Therefore, the first people to enter North America could not have migrated through an ice-free corridor along the eastern slopes of the Rockies. Assuming they entered the Americas during the last ice age, then the most likely route would be down the coast of Alaska and British Columbia. Interestingly, this hypothesis was proposed by the director of the 1983 Tse’K’wa excavations, Knut Fladmark, in a paper published in 1979!   The Tse’K’wa stone artifacts lend support to this scenario. The earliest spear point at the site – the “fluted point” – is stylistically very similar to artifacts found in the south, which date a little earlier than those at Tse’K’wa. This supports the notion that the earliest inhabitants of the site were part of a human population that began to move north (perhaps out of southern Alberta and northern Montana)  following the bison herds as they moved north to exploit the newly created grassland environments that formed as ice melted and glacial lakes drained away

Local and Global Distinguishability in Quantum Interferometry

A statistical distinguishability based on relative entropy characterises the fitness of quantum states for phase estimation. This criterion is employed in the context of a Mach-Zehnder interferometer and used to interpolate between two regimes, of local and global phase distinguishability. The scaling of distinguishability in these regimes with photon number is explored for various quantum states. It emerges that local distinguishability is dependent on a discrepancy between quantum and classical rotational energy. Our analysis demonstrates that the Heisenberg limit is the true upper limit for local phase sensitivity. Only the `NOON' states share this bound, but other states exhibit a better trade-off when comparing local and global phase regimes.Comment: 4 pages, in submission, minor revision

Effects of noise on convergent game learning dynamics

We study stochastic effects on the lagging anchor dynamics, a reinforcement learning algorithm used to learn successful strategies in iterated games, which is known to converge to Nash points in the absence of noise. The dynamics is stochastic when players only have limited information about their opponents' strategic propensities. The effects of this noise are studied analytically in the case where it is small but finite, and we show that the statistics and correlation properties of fluctuations can be computed to a high accuracy. We find that the system can exhibit quasicycles, driven by intrinsic noise. If players are asymmetric and use different parameters for their learning, a net payoff advantage can be achieved due to these stochastic oscillations around the deterministic equilibrium.Comment: 17 pages, 8 figure

21-cm cosmology

Imaging the Universe during the first hundreds of millions of years remains one of the exciting challenges facing modern cosmology. Observations of the redshifted 21 cm line of atomic hydrogen offer the potential of opening a new window into this epoch. This would transform our understanding of the formation of the first stars and galaxies and of the thermal history of the Universe. A new generation of radio telescopes is being constructed for this purpose with the first results starting to trickle in. In this review, we detail the physics that governs the 21 cm signal and describe what might be learnt from upcoming observations. We also generalize our discussion to intensity mapping of other atomic and molecular lines.Comment: 64 pages, 20 figures, submitted to Reports on Progress in Physics, comments welcom

Sympatric Speciation: When Is It Possible in Bacteria?

This study investigated a potential auditory illusion in duration perception induced by rhythmic temporal contexts. Listeners with or without musical training performed a duration discrimination task for a silent period in a rhythmic auditory sequence. The critical temporal interval was presented either within a perceptual group or between two perceptual groups. We report the just-noticeable difference (difference limen, DL) for temporal intervals and the point of subjective equality (PSE) derived from individual psychometric functions based on performance of a two-alternative forced choice task. In musically untrained individuals, equal temporal intervals were perceived as significantly longer when presented between perceptual groups than within a perceptual group (109.25% versus 102.5% of the standard duration). Only the perceived duration of the between-group interval was significantly longer than its objective duration. Musically trained individuals did not show this effect. However, in both musically trained and untrained individuals, the relative difference limens for discriminating the comparison interval from the standard interval were larger in the between-groups condition than in the within-group condition (7.3% vs. 5.6% of the standard duration). Thus, rhythmic grouping affected sensitivity to duration changes in all listeners, with duration differences being harder to detect at boundaries of rhythm groups than within rhythm groups. Our results show for the first time that temporal Gestalt induces auditory duration illusions in typical listeners, but that musical experts are not susceptible to this effect of rhythmic grouping.Ellison Medical FoundationSwiss National Science Foundation (PA00P1_131448/1

Platelet factor XIII-A regulates platelet function and promotes clot retraction and stability.

Factor XIII (FXIII) is an important proenzyme in the hemostatic system. The plasma-derived enzyme activated FXIII cross-links fibrin fibers within thrombi to increase their mechanical strength and cross-links fibrin to fibrinolytic inhibitors, specifically α2-antiplasmin, to increase resistance to fibrinolysis. We have previously shown that cellular FXIII (factor XIII-A [FXIII-A]), which is abundant in the platelet cytoplasm, is externalized onto the activated membrane and cross-links extracellular substrates. The contribution of cellular FXIII-A to platelet activation and platelet function has not been extensively studied. This study aims to identify the role of platelet FXIII-A in platelet function. We used normal healthy platelets with a cell permeable FXIII inhibitor and platelets from FXIII-deficient patients as a FXIII-free platelet model in a range of platelet function and clotting tests. Our data demonstrate that platelet FXIII-A enhances fibrinogen binding to the platelet surface upon agonist stimulation and improves the binding of platelets to fibrinogen and aggregation under flow in a whole-blood thrombus formation assay. In the absence of FXIII-A, platelets show reduced sensitivity to agonist stimulation, including decreased P-selectin exposure and fibrinogen binding. We show that FXIII-A is involved in platelet spreading where a lack of FXIII-A reduces the ability of platelets to fully spread on fibrinogen and collagen. Our data demonstrate that platelet FXIII-A is important for clot retraction where clots formed in its absence retracted to a lesser extent. Overall, this study shows that platelet FXIII-A functions during thrombus formation by aiding platelet activation and thrombus retraction in addition to its antifibrinolytic roles

Therapy development for the mucopolysaccharidoses : updated consensus recommendations for neuropsychological endpoints

Neurological dysfunction represents a significant clinical component of many of the mucopolysaccharidoses (also known as MPS disorders). The accurate and consistent assessment of neuropsychological function is essential to gain a greater understanding of the precise natural history of these conditions and to design effective clinical trials to evaluate the impact of therapies on the brain. In 2017, an International MPS Consensus Panel published recommendations for best practice in the design and conduct of clinical studies investigating the effects of therapies on cognitive function and adaptive behavior in patients with neuronopathic mucopolysaccharidoses. Based on an International MPS Consensus Conference held in February 2020, this article provides updated consensus recommendations and expands the objectives to include approaches for assessing behavioral and social-emotional state, caregiver burden and quality of life in patients with all mucopolysaccharidoses

The Mock LISA Data Challenges: from Challenge 3 to Challenge 4

The Mock LISA Data Challenges are a program to demonstrate LISA data-analysis capabilities and to encourage their development. Each round of challenges consists of one or more datasets containing simulated instrument noise and gravitational waves from sources of undisclosed parameters. Participants analyze the datasets and report best-fit solutions for the source parameters. Here we present the results of the third challenge, issued in Apr 2008, which demonstrated the positive recovery of signals from chirping Galactic binaries, from spinning supermassive--black-hole binaries (with optimal SNRs between ~ 10 and 2000), from simultaneous extreme-mass-ratio inspirals (SNRs of 10-50), from cosmic-string-cusp bursts (SNRs of 10-100), and from a relatively loud isotropic background with Omega_gw(f) ~ 10^-11, slightly below the LISA instrument noise.Comment: 12 pages, 2 figures, proceedings of the 8th Edoardo Amaldi Conference on Gravitational Waves, New York, June 21-26, 200