The late winter diets of barren-ground caribou in North-Central Canada

Rumen samples from 104 barren-ground caribou (Rangifer tarandus groenlandicus) collected in March 1980 and 1981 at 18 sites on the winter range in south-central Northwest Territories (NWT) and northern Saskatchewan were examined microscopically for relative occurrence of plant fragments. The composition of plant fragments in the rumens of calves did not differ from that in older caribou. Samples were homogeneous within sites and among them. Therefore we analyzed composite samples for each site and then pooled the data. Terricolous fruticose and foliose lichens averaged 68.5 ± 1.5% (SE) ot tallied fragments at all 18 sites, followed by conifer needles (11.9 ± 1.2%), green leaves of Vactinium spp., Ledum spp., and other shrubs and iorbs (5.6 ± 0.6%), twigs and bark (5.5 ± 0.4%), bryophytes (4.9 ± 0.6%) and 3.6% unidentified. The lichen component consisted of 8.4 ± 1.5% Stereocaulon spp., 46.9 ± 2.6% other fruticose lichens (largely Cladina spp., Cladonia spp., and Cetraria spp.), and 13.2 ± 1.5% foliose lichens (largely Peltigera spp.). A comparison of rumen contents with the average relative abundance of plants found in feeding craters at 13 sites suggests that use of plant species was not always proportionate to their occurrence

In Vitro Digestibilities of Plants Utilized by Barren-Ground Caribou

Rumen fluids of barren-ground caribou (Rangifer tarandus groenlandicus) were used with standard in vitro procedures in March 1981 to investigate the relative digestibilities of forages collected on caribou winter ranges in the southern Northwest Territories. In vitro dry matter disappearance (IVDMD) of the three most abundant arboreal lichens, when fermented in test tubes for 60 h, averaged 67% compared with 43% for the seven most common terricolous lichens. The DMD of leaves of the most common shrubs, Vaccinium vitis-idaea, Empetrum nigrum, Arctostaphylos spp., and Ledum spp. averaged 46% (37-51%). Eight bryophyte species averaged 17% (7-28%) DMD. The DMD of species of three lichen genera with low protein contents, Cladina, Cladonia, and Cetraria, continued to increase with increasing fermentation periods up to 180 h. Nine species of lichens averaged 49% DMD when fermented for 60 h in test tubes, 64% when fermented in Erlenmeyer flasks, and 76% when 60 mg of urea was added to flasks. DMDs of 22 plant species were significantly higher in March 1981 than in similar tests conducted one year earlier. This annual variation in the digestive capacities of ruminal fluids was associated with the physical condition of the caribou and may have been related to their nutritional history.Key words: Canada, caribou, digestibilities, in vitro, lichens, nutrition, RangiferMots clés: Canada, caribou, digestibilité, in vitro, lichens, nutrition, Rangife

Genomics, environment and balancing selection in behaviorally bimodal populations : the caribou case

Selection forces that favor different phenotypes in different environments can change frequencies of genes between populations along environmental clines. Clines are also compatible with balancing forces, such as negative frequency‐dependent selection (NFDS), which maintains phenotypic polymorphisms within populations. For example, NFDS is hypothesized to maintain partial migration, a dimorphic behavioral trait prominent in species where only a fraction of the population seasonally migrates. Overall, NFDS is believed to be a common phenomenon in nature, yet, a scarcity of studies were published linking naturally occurring allelic variation with bimodal or multimodal phenotypes and balancing selection. We applied a Pool‐seq approach and detected selection on alleles associated with environmental variables along a North‐South gradient in western North American caribou, a species displaying partially migratory behavior. On 51 loci, we found a signature of balancing selection, which could be related to NFDS and ultimately the maintenance of the phenotypic polymorphisms known within these populations. Yet, remarkably, we detected directional selection on a locus when our sample was divided in two behaviorally distinctive groups regardless of geographic provenance (a subset of GPS‐collared migratory or sedentary individuals), indicating that, within populations, phenotypically homogeneous groups were genetically distinctive. Loci under selection were linked to functional genes involved in oxidative stress response, body development and taste perception. Overall, results indicated genetic differentiation along an environmental gradient of caribou populations, which we found characterized by genes potentially undergoing balancing selection. We suggest that the underlining balancing force, NFDS plays a strong role within populations harboring multiple haplotypes and phenotypes, as it is the norm in animals, plants and humans too

Dynamics in electron-impact ionization of H(2)O

We present multiply differential cross sections for electron-impact ionization of the water molecule. The experimental results are compared with theoretical cross sections calculated using a recently developed distorted-wave Born approach for molecules. The experimental cross sections exhibit a very large recoil scattering, which is not predicted by the theory. This has implications for applications of this theoretical approach in areas such as modeling of ionization in biological systems.D. S. Milne-Brownlie, S. J. Cavanagh, Birgit Lohmann, C. Champion, P. A. Hervieux, and J. Hansse

Comment on “Experimental and theoretical study of the triple-differential cross section for electron-impact ionization of thymine molecules”

In their recent paper, Bellm et al. [Phys. Rev. A 85, 022710 (2012)] performed (e,2e) experiments on thymine at an incident energy of 250 eV. They wrote in the conclusion that a model based on the first Born approximation using the completely neglected differential overlap description is in very good agreement with the experimental data. On the contrary, we argue that this model fails to describe experiments on water performed at the same incident energy and is unable to explain any shift of the binary or recoil peaks

Optimal protocols and universal time-energy bound in Brownian thermodynamics

We propose an optimization strategy to control the dynamics of a stochastic system transferred from one thermal equilibrium to another and apply it experimentally to a Brownian particle in an optical trap under compression. Based on a variational principle that treats the transfer duration and the expended work on an equal footing, our strategy leads to a family of protocols that are either optimally cheap for a given duration or optimally fast for a given energetic cost. This approach unveils a universal relation $\Delta t\,\Delta W \ge (\Delta t\,\Delta W)_{\rm opt}$ between the transfer duration and the expended work. We verify experimentally that the lower bound is reached only with the optimized protocols.Comment: 10 pages, 14 figure

Development of a PbWO4 Detector for Single-Shot Positron Annihilation Lifetime Spectroscopy at the GBAR Experiment

We have developed a PbWO4 (PWO) detector with a large dynamic range to measure the intensity of a positron beam and the absolute density of the ortho-positronium (o-Ps) cloud it creates. A simulation study shows that a setup based on such detectors may be used to determine the angular distribution of the emission and reflection of o-Ps to reduce part of the uncertainties of the measurement. These will allow to improve the precision in the measurement of the cross-section for the (anti)hydrogen formation by (anti)proton-positronium charge exchange and to optimize the yield of antihydrogen ion which is an essential parameter in the GBAR experiment