Evolutionary biology: sex change and relative body size in animals

Organisms that change sex during their lifetime use a variety of strategies--they may be female first, male first or even repetitive sex changers. Natural selection should favour those individuals that change sex at a time when it increases their reproductive value. Allsop and West claim that the relative timing of sex change is invariant across all animals, with individuals changing sex at 72% of their maximum body size, and infer that natural selection for sex change must therefore be fundamentally similar across animals. Here we explain why we believe that Allsop and West's claims are not supported by their analysis or by their empirical data.     

Epigenetics in human disease and prospects for epigenetic therapy

Epigenetic mechanisms, which involve DNA and histone modifications, result in the heritable silencing of genes without a change in their coding sequence. The study of human disease has focused on genetic mechanisms, but disruption of the balance of epigenetic networks can cause several major pathologies, including cancer, syndromes involving chromosomal instabilities, and mental retardation. The development of new diagnostic tools might reveal other diseases that are caused by epigenetic alterations. Great potential lies in the development of 'epigenetic therapies'--several inhibitors of enzymes controlling epigenetic modifications, specifically DNA methyltransferases and histone deacetylases, have shown promising anti-tumorigenic effects for some malignancies.     

VEGF delivery with retrogradely transported lentivector prolongs survival in a mouse ALS model

Amyotrophic lateral sclerosis (ALS) causes adult-onset, progressive motor neuron degeneration in the brain and spinal cord, resulting in paralysis and death three to five years after onset in most patients. ALS is still incurable, in part because its complex aetiology remains insufficiently understood. Recent reports have indicated that reduced levels of vascular endothelial growth factor (VEGF), which is essential in angiogenesis and has also been implicated in neuroprotection, predispose mice and humans to ALS. However, the therapeutic potential of VEGF for the treatment of ALS has not previously been assessed. Here we report that a single injection of a VEGF-expressing lentiviral vector into various muscles delayed onset and slowed progression of ALS in mice engineered to overexpress the gene coding for the mutated G93A form of the superoxide dismutase-1 (SOD1(G93A)) (refs 7-10), even when treatment was only initiated at the onset of paralysis. VEGF treatment increased the life expectancy of ALS mice by 30 per cent without causing toxic side effects, thereby achieving one of the most effective therapies reported in the field so far.     

Millennial and orbital variations of El Niño/Southern Oscillation and high-latitude climate in the last glacial period

The El Ni?o/Southern Oscillation (ENSO) phenomenon is believed to have operated continuously over the last glacial-interglacial cycle. ENSO variability has been suggested to be linked to millennial-scale oscillations in North Atlantic climate during that time, but the proposals disagree on whether increased frequency of El Ni?o events, the warm phase of ENSO, was linked to North Atlantic warm or cold periods. Here we present a high-resolution record of surface moisture, based on the degree of peat humification and the ratio of sedges to grass, from northern Queensland, Australia, covering the past 45,000 yr. We observe millennial-scale dry periods, indicating periods of frequent El Ni?o events (summer precipitation declines in El Ni?o years in northeastern Australia). We find that these dry periods are correlated to the Dansgaard-Oeschger events--millennial-scale warm events in the North Atlantic climate record--although no direct atmospheric connection from the North Atlantic to our site can be invoked. Additionally, we find climatic cycles at a semiprecessional timescale (approximately 11,900 yr). We suggest that climate variations in the tropical Pacific Ocean on millennial as well as orbital timescales, which determined precipitation in northeastern Australia, also exerted an influence on North Atlantic climate through atmospheric and oceanic teleconnections.     

商业伦理的形而上学基础

考虑到形而上学和伦理的原则是人类所有理论知识与实践选择的首要而有效的方法,通过考察古代对形而上学和商业伦理的哲学反思,人自身、人的才能和商业伦理,西塞罗、亚里士多德和中世纪关于人自身的反思,训练智力和伦理美德的商业教育,从无创造、道成肉身和现代商业伦理,基督教、有限管理和现代商业伦理,现代企业的成功及商业伦理等,揭示出健康的政治经济秩序是建立在好的形而上学原则之上的.     

Determinants of woody cover in African savannas

Savannas are globally important ecosystems of great significance to human economies. In these biomes, which are characterized by the co-dominance of trees and grasses, woody cover is a chief determinant of ecosystem properties. The availability of resources (water, nutrients) and disturbance regimes (fire, herbivory) are thought to be important in regulating woody cover, but perceptions differ on which of these are the primary drivers of savanna structure. Here we show, using data from 854 sites across Africa, that maximum woody cover in savannas receiving a mean annual precipitation (MAP) of less than approximately 650 mm is constrained by, and increases linearly with, MAP. These arid and semi-arid savannas may be considered 'stable' systems in which water constrains woody cover and permits grasses to coexist, while fire, herbivory and soil properties interact to reduce woody cover below the MAP-controlled upper bound. Above a MAP of approximately 650 mm, savannas are 'unstable' systems in which MAP is sufficient for woody canopy closure, and disturbances (fire, herbivory) are required for the coexistence of trees and grass. These results provide insights into the nature of African savannas and suggest that future changes in precipitation may considerably affect their distribution and dynamics.     

Global hotspots of species richness are not congruent with endemism or threat

Biodiversity hotspots have a prominent role in conservation biology, but it remains controversial to what extent different types of hotspot are congruent. Previous studies were unable to provide a general answer because they used a single biodiversity index, were geographically restricted, compared areas of unequal size or did not quantitatively compare hotspot types. Here we use a new global database on the breeding distribution of all known extant bird species to test for congruence across three types of hotspot. We demonstrate that hotspots of species richness, threat and endemism do not show the same geographical distribution. Only 2.5% of hotspot areas are common to all three aspects of diversity, with over 80% of hotspots being idiosyncratic. More generally, there is a surprisingly low overall congruence of biodiversity indices, with any one index explaining less than 24% of variation in the other indices. These results suggest that, even within a single taxonomic class, different mechanisms are responsible for the origin and maintenance of different aspects of diversity. Consequently, the different types of hotspots also vary greatly in their utility as conservation tools.     

Trace element signature of subduction-zone fluids, melts and supercritical liquids at 120-180 km depth

Fluids and melts liberated from subducting oceanic crust recycle lithophile elements back into the mantle wedge, facilitate melting and ultimately lead to prolific subduction-zone arc volcanism. The nature and composition of the mobile phases generated in the subducting slab at high pressures have, however, remained largely unknown. Here we report direct LA-ICPMS measurements of the composition of fluids and melts equilibrated with a basaltic eclogite at pressures equivalent to depths in the Earth of 120-180 km and temperatures of 700-1,200 degrees C. The resultant liquid/mineral partition coefficients constrain the recycling rates of key elements. The dichotomy of dehydration versus melting at 120 km depth is expressed through contrasting behaviour of many trace elements (U/Th, Sr, Ba, Be and the light rare-earth elements). At pressures equivalent to 180 km depth, however, a supercritical liquid with melt-like solubilities for the investigated trace elements is observed, even at low temperatures. This mobilizes most of the key trace elements (except the heavy rare-earth elements, Y and Sc) and thus limits fluid-phase transfer of geochemical signatures in subduction zones to pressures less than 6 GPa.