The Parallel Magnetoconductance of Interacting Electrons in a Two Dimensional Disordered System

The transport properties of interacting electrons for which the spin degree of freedom is taken into account are numerically studied for small two dimensional diffusive clusters. On-site electron-electron interactions tend to delocalize the electrons, while long-range interactions enhance localization. On careful examination of the transport properties, we reach the conclusion that it does not show a two dimensional metal insulator transition driven by interactions. A parallel magnetic field leads to enhanced resistivity, which saturates once the electrons become fully spin polarized. The strength of the magnetic field for which the resistivity saturates decreases as electron density goes down. Thus, the numerical calculations capture some of the features seen in recent experimental measurements of parallel magnetoconductance.Comment: 10 pages, 6 figure

An updated radiocarbon-based ice margin chronology for the last deglaciation of the North American Ice Sheet Complex

The North American Ice Sheet Complex (NAISC; consisting of the Laurentide, Cordilleran and Innuitian ice sheets) was the largest ice mass to repeatedly grow and decay in the Northern Hemisphere during the Quaternary. Understanding its pattern of retreat following the Last Glacial Maximum is critical for studying many facets of the Late Quaternary, including ice sheet behaviour, the evolution of Holocene landscapes, sea level, atmospheric circulation, and the peopling of the Americas. Currently, the most up-to-date and authoritative margin chronology for the entire ice sheet complex is featured in two publications (Geological Survey of Canada Open File 1574 [Dyke et al., 2003]; ‘Quaternary Glaciations – Extent and Chronology, Part II’ [Dyke, 2004]). These often-cited datasets track ice margin recession in 36 time slices spanning 18 ka to 1 ka (all ages in uncalibrated radiocarbon years) using a combination of geomorphology, stratigraphy and radiocarbon dating. However, by virtue of being over 15 years old, the ice margin chronology requires updating to reflect new work and important revisions. This paper updates the aforementioned 36 ice margin maps to reflect new data from regional studies. We also update the original radiocarbon dataset from the 2003/2004 papers with 1541 new ages to reflect work up to and including 2018. A major revision is made to the 18 ka ice margin, where Banks and Eglinton islands (once considered to be glacial refugia) are now shown to be fully glaciated. Our updated 18 ka ice sheet increased in areal extent from 17.81 to 18.37 million km2, which is an increase of 3.1% in spatial coverage of the NAISC at that time. Elsewhere, we also summarize, region-by-region, significant changes to the deglaciation sequence. This paper integrates new information provided by regional experts and radiocarbon data into the deglaciation sequence while maintaining consistency with the original ice margin positions of Dyke et al. (2003) and Dyke (2004) where new information is lacking; this is a pragmatic solution to satisfy the needs of a Quaternary research community that requires up-to-date knowledge of the pattern of ice margin recession of what was once the world’s largest ice mass. The 36 updated isochrones are available in PDF and shapefile format, together with a spreadsheet of the expanded radiocarbon dataset (n = 5195 ages) and estimates of uncertainty for each interval

An extended mtDNA phylogeography for the alpine newt illuminates the provenance of introduced populations

Many herpetofauna species have been introduced outside of their native range. MtDNA barcoding is regularly used to determine the provenance of such populations. The alpine newt has been introduced across the Netherlands, the United Kingdom and Ireland. However, geographical mtDNA structure across the natural range of the alpine newt is still incompletely understood and certain regions are severely undersampled. We collect mtDNA sequence data of over seven hundred individuals, from both the native and the introduced range. The main new insights from our extended mtDNA phylogeography are that 1) haplotypes from Spain do not form a reciprocally monophyletic clade, but are nested inside the mtDNA clade that covers western and eastern Europe; and 2) haplotypes from the northwest Balkans form a monophyletic clade together with those from the Southern Carpathians and Apuseni Mountains. We also home in on the regions where the distinct mtDNA clades meet in nature. We show that four out of the seven distinct mtDNA clades that comprise the alpine newt are implicated in the introductions in the Netherlands, United Kingdom and Ireland. In several introduced localities, two distinct mtDNA clades co-occur. As these mtDNA clades presumably represent cryptic species, we urge that the extent of genetic admixture between them is assessed from genome-wide nuclear DNA markers. We mobilized a large number of citizen scientists in this project to support the collection of DNA samples by skin swabbing and underscore the effectiveness of this sampling technique for mtDNA barcoding

Pollen and nectar sources near Rimouski, Quebec, Canada

In 1980, the study of pollen yields and honeys from the same hive was conducted near Rimouski, in the Lower Saint-Laurence River region (fig 1). Pollen yields were collected daily using a trap placed on a new colony. Half of the yields were examined through sorting of pellets (Louveaux, 1958a). Honey samples, covering one week each, were extracted at the end of the season using photographic comparison of honeycombs. Standard meteorological data were recorded daily, and weekly surveys of flowering plants were performed within a 1.5 km radius around the apiary (fig 1). A total of 1 226 g of fresh pollen were extracted from the trap during a 3.5 mth period (table I). Considering the trap efficiency, around 12.5 kg of fresh pollen were collected by the bees for a mean of 3.6 kg/mo. This result is remarkable, considering the restraints imposed on the colony and the bad weather conditions of 1980. On 60 taxa identified in the pellets (fig 2), only 16 displayed individual values greater than 1% of the total pollen crop (table II). The main pollen sources (> 10%) were : Trifolium hybridum / T repens, Cornus stolonifera, and Salix spp. Mixed pollen pellets were recorded in 65% of pollen yields but they represent only 0.4% of the total yield. Thirty-six (36) taxa were identified in mixed pellets (table III). Pollen analysis of 13 successive honeys and 3 annual ones from the same apiary showed the presence of 42 taxa (fig 3). Other information about these honeys is given in table IV. Most of the honeys are poor in pollen grains. Honeys from the beginning of the season are mixed floral; they are replaced by Rubus idaeus monofloral honeys and then by mixed honeys preceding monofloral honeys of Trifolium hybridum / T repens. The last successive honey presents a double dominance with Medicago sativa. Rubus and Trifolium association is also found in the 3 annual honeys. Pollen analysis of successive honeys has demonstrated the contamination of honey by pollen which is part of the bees diet. These phenomena, caused by the bees, would explain the presence in honey of species without floral nectaries and species which were no longer in bloom when the honey super was installed. Most of the plants selected by the bees were present within 500 m of the apiary, were selected from the indigenous or naturalised flora and were visited for both pollen and nectar (table V)

Cuora mouhotii (Gray 1862) – Keeled Box Turtle

– The Keeled Box Turtle, Cuora mouhotii (Family Geoemydidae), is a small (carapace length up to ca. 250 mm), once poorly-known terrestrial species. Recent extensive research on the species in its natural habitat in northern Vietnam and Hainan, China, has significantly increased available knowledge of the species. Cuora mouhotii is a highly terrestrial turtle from the mesic forests of Southeast Asia. Two subspecies have been described, and intergradient populations are known. Relatively widespread, it is apparently abundant nowhere. Omnivorous, at least in captivity, the species is highly carnivorous in the wild but will also take fruit. Clutch size ranges from 1–9 eggs, with egg dimensions ca. 41 x 26 mm; incubation period in captivity varies from 82 to 120 days. Major threats to the species are loss of forest habitat from logging and commercial trade for Traditional Chinese Medicine and food. To a lesser extent capture for local consumption and both national and international pet trade are factors threatening this species

An isolated crested newt population in Dutch coastal dunes: distribution relict or introduction?

Isolated distribution patches may represent local remnants of a formerly wider range or could have originated by human-mediated expansion beyond the natural range. Distinguishing between these two scenarios is not always straightforward. Northern crested newts (Triturus cristatus) in the Dutch coastal dunes are disconnected from the main species range by over 40 kilometres and whether they have been present historically is unclear. We genotyped crested newts from throughout the Netherlands for an mtDNA marker to determine the provenance of the coastal dune population. Because a closely related species, the Italian crested newt (T. carnifex), has an introduction history in the Netherlands, we also screened eight nuclear DNA SNP markers diagnostic for T. cristatus vs. T. carnifex. The crested newts from the coastal dunes carry a single T. cristatus mtDNA haplotype that naturally occurs in the south, but not the east, of the Netherlands. Therefore, we cannot distinguish if the population represents a natural distribution relict or is derived from an introduction. We find no evidence of genetic admixture with T. carnifex in the coastal dunes, but such admixture is apparent at another Dutch locality (far removed from a previously known genetically admixed population). Our study illustrates how difficult it can be to determine the origin of isolated populations. </p