The Complex Demographic History and Evolutionary Origin of the Western Honey Bee, Apis Mellifera.

The western honey bee, Apis mellifera, provides critical pollination services to agricultural crops worldwide. However, despite substantial interest and prior investigation, the early evolution and subsequent diversification of this important pollinator remain uncertain. The primary hypotheses place the origin of A. mellifera in either Asia or Africa, with subsequent radiations proceeding from one of these regions. Here, we use two publicly available whole-genome data sets plus newly sequenced genomes and apply multiple population genetic analysis methods to investigate the patterns of ancestry and admixture in native honey bee populations from Europe, Africa, and the Middle East. The combination of these data sets is critical to the analyses, as each contributes samples from geographic locations lacking in the other, thereby producing the most complete set of honey bee populations available to date. We find evidence supporting an origin of A. mellifera in the Middle East or North Eastern Africa, with the A and Y lineages representing the earliest branching lineages. This finding has similarities with multiple contradictory hypotheses and represents a disentangling of genetic relationships, geographic proximity, and secondary contact to produce a more accurate picture of the origins of A. mellifera. We also investigate how previous studies came to their various conclusions based on incomplete sampling of populations, and illustrate the importance of complete sampling in understanding evolutionary processes. These results provide fundamental knowledge about genetic diversity within Old World honey bee populations and offer insight into the complex history of an important pollinator

p-Type semiconducting properties in lithium-doped MgO single crystals

The phenomenally large enhancement in conductivity observed when Li-doped MgO crystals are oxidized at elevated temperatures was investigated by dc and ac electrical measurements in the temperature interval 250-673 K. The concentration of ([Li]^{0}) centers (Li^{+} ions each with a trapped hole) resulting from oxidation was monitored by optical absorption measurements. Both dc and ac experiments provide consistent values for the bulk resistance. The electricalconductivity of oxidized MgO:Li crystals increases linearly with the concentration of ([Li]^{0}) centers. The conductivity is thermally activated with an activation energy of (0.70 +/- 0.01) eV, which is independent of the ([Li]^{0}) content. The \textit{standard semiconducting} mechanism satisfactorily explains these results. Free holes are the main contribution to band conduction as they are trapped at or released from the ([Li]^{0})-acceptor centers. In as-grown MgO:Li crystals, electrical current increases dramatically with time due to the formation of ([Li]^{0}) centers. The activation energy values between 1.3 and 0.7 eV are likely a combination of the activation energy for the creation of ([Li]^{0}) centers and the activation energy of ionization of these centers. Destruction of ([Li]^{0}) centers can be induced in oxidized crystals by application of an electric field due to Joule heating up to temperatures at which ([Li]^{0}) centers are not stable.Comment: LaTeX, 20 pages, 9 Encapsulated Postscript Format Figures, use the version 4.0 of REVTEX 4 macro packag

Characterization of the known T type dwarfs towards the Sigma Orionis cluster

(Abridged) A total of three T type candidates (SOri70, SOri73, and SOriJ0538-0213) lying in the line of sight towards Sigma Orionis were characterized by means of near-infrared photometric, astrometric, and spectroscopic studies. H-band methane images were collected for all three sources and an additional sample of 15 field T type dwarfs using LIRIS/WHT. J-band spectra of resolution of ~500 were obtained for SOriJ0538-0213 with ISAAC/VLT, and JH spectra of resolution of ~50 acquired with WFC3/HST were employed for the spectroscopic classification of SOri70 and 73. Proper motions with a typical uncertainty of +/-3 mas/yr and a time interval of ~7-9 yr were derived. Using the LIRIS observations of the field T dwarfs, we calibrated this imager for T spectral typing via methane photometry. The three SOri objects were spectroscopically classified as T4.5+/-0.5 (SOri73), T5+/-0.5 (SOriJ0538-0213), and T7$^{+0.5}_{-1.0}$ (SOri70). The similarity between the observed JH spectra and the methane colors and the data of field ultra-cool dwarfs of related classifications suggests that SOri70, 73, and SOriJ053804.65-021352.5 do not deviate significantly in surface gravity in relation to the field. Additionally, the detection of KI at ~1.25 microns in SOriJ0538-0213 points to a high-gravity atmosphere. Only the K-band reddish nature of SOri70 may be consistent with a low gravity atmosphere. The proper motions of SOri70 and 73 are measurable and are larger than that of the cluster by >3.5 sigma. The proper motion of SOriJ0538-0213 is consistent with a null displacement. These observations suggest that none of the three T dwarfs are likely Sigma Orionis members, and that either planetary-mass objects with masses below ~4 MJup may not exist free-floating in the cluster or they may lie at fainter near-infrared magnitudes than those of the targets (this is H>20.6 mag), thus remaining unidentified to date.Comment: Accepted for publication in A&A (2014), corrected typo

Hydrogen and muonium in diamond: A path-integral molecular dynamics simulation

Isolated hydrogen, deuterium, and muonium in diamond have been studied by path-integral molecular dynamics simulations in the canonical ensemble. Finite-temperature properties of these point defects were analyzed in the range from 100 to 800 K. Interatomic interactions were modeled by a tight-binding potential fitted to density-functional calculations. The most stable position for these hydrogenic impurities is found at the C-C bond center. Vibrational frequencies have been obtained from a linear-response approach, based on correlations of atom displacements at finite temperatures. The results show a large anharmonic effect in impurity vibrations at the bond center site, which hardens the vibrational modes with respect to a harmonic approximation. Zero-point motion causes an appreciable shift of the defect level in the electronic gap, as a consequence of electron-phonon interaction. This defect level goes down by 70 meV when replacing hydrogen by muonium.Comment: 11 pages, 8 figure