Molecular and Historical Aspects of Corn Belt Dent Diversity

Tens-of-thousands of open-pollinated cultivars of corn (Zea mays L.) are being maintained in germplasm banks. Knowledge of the amount and distribution of genetic variation within and among accessions can aid end users in choosing among them. We estimated molecular genetic variation and looked for influences of pedigree, adaptation, and migration in the genetic makeup of conserved Corn-Belt Dent-related germplasm. Plants sampled from 57 accessions representing Corn-Belt Dents, Northern Flints, Southern Dents, plus 12 public inbreds, were genotyped at 20 simple sequence repeat (SSR) loci. For 47 of the accessions, between 5 and 23 plants per accession were genotyped (mean = 9.3). Mean number of alleles per locus was 6.5 overall, 3.17 within accessions, and 3.20 within pooled inbreds. Mean gene diversity was 0.53 within accessions and 0.61 within pooled inbreds. Open-pollinated accessions showed a tendency toward inbreeding (FIS = 0.09), and 85% of genetic variation was shared among them. A Fitch-Margoliash tree strongly supported the distinctiveness of flint from dent germplasm but did not otherwise reveal evidence of genetic structure. Mantel tests revealed significant correlations between genetic distance and geographical (r = 0.54, P= 0.04) or maturity zone (r = 0.33, P = 0.03) distance only if flint germplasm was included in the analyses. A significant correlation (r = 0.76, P \u3c 0.01) was found between days to pollen shed and maturity zone of accession origin. Pedigree, rather than migration or selection, has most influenced the genetic structure of the extant representatives of the open-pollinated cultivars at these SSR loci

Space Telescope and Optical Reverberation Mapping Project. VII. Understanding the Ultraviolet Anomaly in NGC 5548 with X-Ray Spectroscopy

During the Space Telescope and Optical Reverberation Mapping Project observations of NGC 5548, the continuum and emission-line variability became decorrelated during the second half of the six-month-long observing campaign. Here we present Swift and Chandra X-ray spectra of NGC 5548 obtained as part of the campaign. The Swift spectra show that excess flux (relative to a power-law continuum) in the soft X-ray band appears before the start of the anomalous emission-line behavior, peaks during the period of the anomaly, and then declines. This is a model-independent result suggesting that the soft excess is related to the anomaly. We divide the Swift data into on- and off-anomaly spectra to characterize the soft excess via spectral fitting. The cause of the spectral differences is likely due to a change in the intrinsic spectrum rather than to variable obscuration or partial covering. The Chandra spectra have lower signal-to-noise ratios, but are consistent with the Swift data. Our preferred model of the soft excess is emission from an optically thick, warm Comptonizing corona, the effective optical depth of which increases during the anomaly. This model simultaneously explains all three observations: the UV emission-line flux decrease, the soft-excess increase, and the emission-line anomaly

First record of a Jurassic mammal [?'Peramura'] from Ethiopia

The first record of Mesozoic mammals in Ethiopia is a fragment of a lower mammalian molar discovered in residues left after acid dissociation of a small (ca. 4 kg) geological hand sample of a fine−grained bone bed in the lower part of the Mugher Mudstone exposed in the valley of the Jema River. This bone bed is part of a series of estuarine to fluvial deposits that are thought to be of Late Jurassic (Tithonian) age. The fragment preserves the trigonid of a molar; the distal part of its crown is missing. Morphological characters of the trigonid indicate the specimen (JEM−5/21) documents the presence of a mammal with a dentition at either a derived pretribosphenic or primitive tribosphenic grade of evolution. Absence of a well developed basal cingulid around the mesial end of the crown argues against phylogenetic relationships to the australosphenidans. Loss of the distal portion of the crown removed characters critical for determining its grade of evolution. The working hypothesis that JEM−5/21 represents a “peramuran” is advanced for testing. Hypotheses that it represents a mammal with a more derived grade of molar evolution or a previously unknown group of mammals cannot be excluded. JEM−5/21 establishes the presence of mammals in Ethiopia during the Late Jurassic, and its discovery identifies a fossil locality warranting thorough future exploration