Hubble Space Telescope Spectroscopy of V471 Tauri: Oversized K Star, Paradoxical White Dwarf

We have used the GHRS onboard the HST to obtain Lyman-alpha spectra of the hot white-dwarf (WD) component of the short-period eclipsing DA+dK2 pre-cataclysmic binary V471 Tauri, a member of the Hyades star cluster. Radial velocities of the WD, combined with ground-based measurements of the dK velocities, eclipse timings, and a determination of the dK star's rotational velocity, yield dynamical masses for the components of M(WD)=0.84 and M(dK)=0.93 Msun. Model-atmosphere fitting of the Ly-alpha profile provides the effective temperature (34,500 K) and surface gravity (log g=8.3) of the WD. The radius of the dK component is 18% larger than that of a normal Hyades dwarf of the same mass. This expansion is attributed to the extensive coverage of the surface by starspots, causing the star to expand in response. The WD radius, determined from a radiometric analysis and from eclipse ingress timings, is 0.0107 Rsun. The position of the star in the M-R plane is in full accord with theory for a degenerate CO WD. The high temperature and mass of the WD present an evolutionary paradox: the WD is the most massive known in the Hyades, but also the hottest and youngest. We suggest that the explanation is that the WD is indeed very young, and is descended from a triple consisting of a blue straggler and a more-distant dK companion. We estimate that the common-envelope efficiency parameter, alpha_CE, was of order 0.3-1.0, in good agreement with recent hydrodynamical simulations.Comment: Astrophysical Journal, in press. 34 text pages, 8 figure

State of the climate in 2018

In 2018, the dominant greenhouse gases released into Earth’s atmosphere—carbon dioxide, methane, and nitrous oxide—continued their increase. The annual global average carbon dioxide concentration at Earth’s surface was 407.4 ± 0.1 ppm, the highest in the modern instrumental record and in ice core records dating back 800 000 years. Combined, greenhouse gases and several halogenated gases contribute just over 3 W m−2 to radiative forcing and represent a nearly 43% increase since 1990. Carbon dioxide is responsible for about 65% of this radiative forcing. With a weak La Niña in early 2018 transitioning to a weak El Niño by the year’s end, the global surface (land and ocean) temperature was the fourth highest on record, with only 2015 through 2017 being warmer. Several European countries reported record high annual temperatures. There were also more high, and fewer low, temperature extremes than in nearly all of the 68-year extremes record. Madagascar recorded a record daily temperature of 40.5°C in Morondava in March, while South Korea set its record high of 41.0°C in August in Hongcheon. Nawabshah, Pakistan, recorded its highest temperature of 50.2°C, which may be a new daily world record for April. Globally, the annual lower troposphere temperature was third to seventh highest, depending on the dataset analyzed. The lower stratospheric temperature was approximately fifth lowest. The 2018 Arctic land surface temperature was 1.2°C above the 1981–2010 average, tying for third highest in the 118-year record, following 2016 and 2017. June’s Arctic snow cover extent was almost half of what it was 35 years ago. Across Greenland, however, regional summer temperatures were generally below or near average. Additionally, a satellite survey of 47 glaciers in Greenland indicated a net increase in area for the first time since records began in 1999. Increasing permafrost temperatures were reported at most observation sites in the Arctic, with the overall increase of 0.1°–0.2°C between 2017 and 2018 being comparable to the highest rate of warming ever observed in the region. On 17 March, Arctic sea ice extent marked the second smallest annual maximum in the 38-year record, larger than only 2017. The minimum extent in 2018 was reached on 19 September and again on 23 September, tying 2008 and 2010 for the sixth lowest extent on record. The 23 September date tied 1997 as the latest sea ice minimum date on record. First-year ice now dominates the ice cover, comprising 77% of the March 2018 ice pack compared to 55% during the 1980s. Because thinner, younger ice is more vulnerable to melting out in summer, this shift in sea ice age has contributed to the decreasing trend in minimum ice extent. Regionally, Bering Sea ice extent was at record lows for almost the entire 2017/18 ice season. For the Antarctic continent as a whole, 2018 was warmer than average. On the highest points of the Antarctic Plateau, the automatic weather station Relay (74°S) broke or tied six monthly temperature records throughout the year, with August breaking its record by nearly 8°C. However, cool conditions in the western Bellingshausen Sea and Amundsen Sea sector contributed to a low melt season overall for 2017/18. High SSTs contributed to low summer sea ice extent in the Ross and Weddell Seas in 2018, underpinning the second lowest Antarctic summer minimum sea ice extent on record. Despite conducive conditions for its formation, the ozone hole at its maximum extent in September was near the 2000–18 mean, likely due to an ongoing slow decline in stratospheric chlorine monoxide concentration. Across the oceans, globally averaged SST decreased slightly since the record El Niño year of 2016 but was still far above the climatological mean. On average, SST is increasing at a rate of 0.10° ± 0.01°C decade−1 since 1950. The warming appeared largest in the tropical Indian Ocean and smallest in the North Pacific. The deeper ocean continues to warm year after year. For the seventh consecutive year, global annual mean sea level became the highest in the 26-year record, rising to 81 mm above the 1993 average. As anticipated in a warming climate, the hydrological cycle over the ocean is accelerating: dry regions are becoming drier and wet regions rainier. Closer to the equator, 95 named tropical storms were observed during 2018, well above the 1981–2010 average of 82. Eleven tropical cyclones reached Saffir–Simpson scale Category 5 intensity. North Atlantic Major Hurricane Michael’s landfall intensity of 140 kt was the fourth strongest for any continental U.S. hurricane landfall in the 168-year record. Michael caused more than 30 fatalities and $25 billion (U.S. dollars) in damages. In the western North Pacific, Super Typhoon Mangkhut led to 160 fatalities and$6 billion (U.S. dollars) in damages across the Philippines, Hong Kong, Macau, mainland China, Guam, and the Northern Mariana Islands. Tropical Storm Son-Tinh was responsible for 170 fatalities in Vietnam and Laos. Nearly all the islands of Micronesia experienced at least moderate impacts from various tropical cyclones. Across land, many areas around the globe received copious precipitation, notable at different time scales. Rodrigues and Réunion Island near southern Africa each reported their third wettest year on record. In Hawaii, 1262 mm precipitation at Waipā Gardens (Kauai) on 14–15 April set a new U.S. record for 24-h precipitation. In Brazil, the city of Belo Horizonte received nearly 75 mm of rain in just 20 minutes, nearly half its monthly average. Globally, fire activity during 2018 was the lowest since the start of the record in 1997, with a combined burned area of about 500 million hectares. This reinforced the long-term downward trend in fire emissions driven by changes in land use in frequently burning savannas. However, wildfires burned 3.5 million hectares across the United States, well above the 2000–10 average of 2.7 million hectares. Combined, U.S. wildfire damages for the 2017 and 2018 wildfire seasons exceeded $40 billion (U.S. dollars)

Duplication and Retention Biases of Essential and Non-Essential Genes Revealed by Systematic Knockdown Analyses

When a duplicate gene has no apparent loss-of-function phenotype, it is commonly considered that the phenotype has been masked as a result of functional redundancy with the remaining paralog. This is supported by indirect evidence showing that multi-copy genes show loss-of-function phenotypes less often than single-copy genes and by direct tests of phenotype masking using select gene sets. Here we take a systematic genome-wide RNA interference approach to assess phenotype masking in paralog pairs in the Caenorhabditis elegans genome. Remarkably, in contrast to expectations, we find that phenotype masking makes only a minor contribution to the low knockdown phenotype rate for duplicate genes. Instead, we find that non-essential genes are highly over-represented among duplicates, leading to a low observed loss-of-function phenotype rate. We further find that duplicate pairs derived from essential and non-essential genes have contrasting evolutionary dynamics: whereas non-essential genes are both more often successfully duplicated (fixed) and lost, essential genes are less often duplicated but upon successful duplication are maintained over longer periods. We expect the fundamental evolutionary duplication dynamics presented here to be broadly applicableclose9

Phylogenetic reassignment of basal cyclostome braconid parasitoid wasps (Hymenoptera) with description of a new, enigmatic Afrotropical tribe with a highly anomalous 28S D2 secondary structure

A new tribe of braconid wasps provisionally included in the Rhyssalinae, Laibaleini trib. nov., type genus Laibalea gen. nov. (type species Laibalea enigmatica sp. nov.), from Kenya and the Central African Republic, is described. A molecular dataset, with emphasis on basally derived taxa based on four gene fragments (28S D2–D3 expansion region, COI barcode, elongation factor 1-alpha and 16S ribosomal DNA), was analysed both alone and in combination with a morphological dataset. Molecular phylogenetic placement of the new species into an existing subfamily is complicated by the extreme sequence divergence of the three sequences obtained for Laibalea. In both the combined sequence analysis and the combined DNA plus morphological tree, Laibalea is recovered as a sister group to the Rhyssalinae plus all non-cyclostome lineage braconids excluding Mesostoinae, Maxfischeriinae and Aphidiinae. A consensus of morphological characters and molecular analyses suggests inclusion of Laibalea either in the otherwise principally Holarctic subfamily Rhyssalinae or perhap more basally, in the principally Gondwanan Mesostoinae s.l., although we cannot exclude the possibility that it might represent a separate basal lineage. We place Laibalea in its own tribe, provisionally included in Rhyssalinae. The DNA sequence data are presented for several genera for the first time. Avga, the type genus of Avgini, is shown not to belong to Mesostoinae s.l. or Hormiinae, but its exact relationships remain uncertain. The generic compositions of Rhyssalinae and Mesostoinae s.l. are revised. Anachyra, Apoavga, Neptihormius, Neoavga and Opiopterus are shown to belong to Mesostoinae s.s. A key to the tribes of Rhyssalinae is provided

Dual origins of functionally distinct O-LM interneurons revealed by differential 5-HT3AR expression

Forebrain circuits rely upon a relatively small but remarkably diverse population of GABAergic interneurons to bind and entrain large principal cell assemblies for network synchronization and rhythmogenesis. Despite the high degree of heterogeneity across cortical interneurons, members of a given subtype typically exhibit homogeneous developmental origins, neuromodulatory response profiles, morphological characteristics, neurochemical signatures, and electrical features. Here we report a surprising divergence amongst hippocampal oriens-lacunosum moleculare (O-LM) projecting interneurons that have hitherto been considered a homogeneous cell population. Combined immunocytochemical, anatomical, and electrophysiological interrogation of Htr3a-GFP and Nkx2-1-cre:RCE mice revealed that O-LM cells parse into caudal ganglionic eminence-derived 5-HT(3A)R-expressing, and medial ganglionic eminence- derived 5-HT(3A)R-lacking subpopulations. These two cohorts differentially participate in network oscillations with 5-HT(3A)R-containing O-LM cell recruitment dictated by serotonergic tone. Thus, members of a seemingly uniform interneuron population can exhibit unique circuit functions and neuromodulatory properties dictated by disparate developmental origins