Liu T.,Tokyo Institute of Technology |
Kinouchi T.,Tokyo Institute of Technology |
Remote Sensing of Environment | Year: 2013
The changing sizes of glaciers in the Cordillera Real (16.2°S, 68.2°W), Bolivian Andes, between 1987 and 2010 were determined by a band ratio method using cloud-free LANDSAT TM and ALOS AVNIR-2 data. From 1987 to 2010, glacier-covered areas in the Cordillera Real were found to have diminished by more than 30%. The rate of glacierized area shrinkage within this Andean region, and particularly of its glaciers, has significantly increased in the past 5. years. To characterize the change in glacierized area, a changing factor k was introduced to capture the effects of topographic factors, including elevation, slope angle, and aspect as identified using ASTER 30-m Global DEM data on the Huayna Potosi, Mururata, Charquini, Illimani, and Serkhe Khollu glaciers. This study also further analyzed the Huayna Potosi glacier and discussed the inhomogeneity of changes in its area with elevation, slope, aspect, and the distribution of solar radiation. © 2013 Elsevier Inc.
The fibula bone (orange) in Dinosaurs is as long as the tibia and reaches down to the ankle (upper left), whereas in adult birds, it is splinter-like and shorter than the tibia, missing its lower end (upper right). However, bird embryos actually start out like dinosaurs, and then develop their adult anatomy (centre). The transformation can be stopped by experimental inhibition of Indian Hedgehog (IHH), a bone maturation gene, which leads to a bird with a dinosaur-like fibula (lower right) Anyone who has eaten roasted chicken can account for the presence of a long, spine-like bone in the drumstick. This is actually the fibula, one of the two long bones of the lower leg (the outer one). In dinosaurs, the ancestors of birds, this bone is tube-shaped and reaches all the way down to the ankle. However, in the evolution from dinosaurs to birds, it lost its lower end, and no longer connects to the ankle, being shorter than the other bone in the lower leg, the tibia. Scientists noted long ago that bird embryos first develop a tubular, dinosaur-like fibula. Afterward, it becomes shorter than the tibia and acquires its adult, splinter-like shape. Brazilian researcher Joâo Botelho, working at the lab of Alexander Vargas (University of Chile) studied the mechanisms that underlie this transformation. In normal bone development, the shaft matures and ceases growth (cell division) long before the ends do. Botelho found that molecular mechanisms of maturation were active very early at the lower end, ceasing cell division and growth. Inhibiting a maturation gene called Indian Hedgehog resulted in chickens with a tubular fibula as long as the tibia and connected to the ankle, just like a dinosaur. Botelho and collaborators believe that early maturation at the lower end of the fibula occurs because of the influence of a nearby bone in the ankle, the calcaneum. Unlike other animals, the calcaneum in bird embryos presses against the lower end of the fibula: They are so close they have even been mistaken for a single element by some researchers. Botelho proposes that at this stage, the lower end of the fibula receives signals more like those at the bone shaft. In normal development, the calcaneum then becomes detached from the fibula. However, its distal end has already become committed to shaft-like development, and matures early. In the chickens with experimentally dinosaur-like lower legs, the calcaneum was attached to the fibula. Botelho also confirmed the calcaneum strongly expresses PthrP, a gene that allows growth at the ends of bones. Another interesting observation in the experimental chickens was that the other bone of the lower leg, the tibia, was significantly shorter. This suggests that a dinosaur-like fibula connected to the ankle stops the tibia from outgrowing the fibula, as it normally would. Working with Jingmai O'Connor (IVPP, China), the research team realized this was consistent with an evolutionary pattern documented by the fossil record. The earliest forms to evolve reduced fibulas were toothed birds from the early cretaceous age, which lived alongside dinosaurs. These forms had splinter-like fibulas that did not connect to the ankle, but were almost as long as the tibia. The fibula first lost its lower end in evolution. This may have allowed the evolution of tibias that are much longer than the fibula, which occurred afterwards. The results of the entire study have been published this week in the renowned academic journal Evolution . This is the second time Botelho has achieved an experimental reversal to a dinosaur-like trait in birds. Previously, he had managed to undo the evolution of the perching toe of birds to produce a non-twisted, non-opposed toe, as in dinosaurs. Another lab at Yale obtained a dinosaur-like snout by altering gene expression in embryonic chicken. However, these studies are not aimed at producing dinosaurs for commercial or non-scientific purposes, as in the Jurassic Park series. "The experiments are focused on single traits to test specific hypotheses," says Vargas. "Not only do we know a great deal about bird development, but also about the dinosaur-bird transition, which is well-documented by the fossil record. This leads naturally to hypotheses on the evolution of development, that can be explored in the lab." More information: João Francisco Botelho et al. Molecular development of fibular reduction in birds and its evolution from dinosaurs, Evolution (2016). DOI: 10.1111/evo.12882 João Francisco Botelho et al. Skeletal plasticity in response to embryonic muscular activity underlies the development and evolution of the perching digit of birds, Scientific Reports (2015). DOI: 10.1038/srep09840 Bhart-Anjan S. Bhullar et al. A molecular mechanism for the origin of a key evolutionary innovation, the bird beak and palate, revealed by an integrative approach to major transitions in vertebrate history, Evolution (2015). DOI: 10.1111/evo.12684
Gilbert A.,IHH |
Gilbert A.,British Petroleum |
Wagnon P.,LGGE |
Wagnon P.,British Petroleum |
And 4 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2010
In June 1999, a deep (138.7 m) ice core was extracted from the summit glacier of Illimani, Bolivia (6340 m above sea level, 16°39'S, 67°47'W), and an englacial temperature profile was measured in the borehole. Using on-site and regional meteorological data as well as ice core stratigraphy, past surface temperatures were reconstructed with a heat flow model. The englacial temperature measurements exhibit a profile that is far from a steady state, reflecting an increasing atmospheric temperature over several years and nonstationary climatic conditions. Englacial temperature interpretation, using air temperature data, borehole temperature inversion, and melting rate quantification based on ice core density, shows two warming phases from 1900 to 1960 (+0.5 ± 0.3 K starting approximately in 1920-1930) and from 1985 to 1999 (+0.6 ± 0.2 K), corresponding to a mean atmospheric temperature rise of 1.1 ± 0.2 K over the 20th century. According to various climate change scenarios, the future evolution of englacial temperatures was simulated to estimate when and under what conditions this high-elevation site on the Illimani summit glacier could become temperate in the future. Results show that this glacier might remain cold for more than 90 years in the case of a +2 K rise over the 21st century but could become temperate in the first 20 m depth between 2050 and 2060 if warming reaches +5 K. Copyright 2010 by the American Geophysical Union.
Sicart J.E.,Joseph Fourier University |
Sicart J.E.,Grenoble Institute of Technology |
Hock R.,University of Alaska Fairbanks |
Hock R.,Uppsala University |
And 3 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2011
A distributed energy balance model was applied to Zongo Glacier, Bolivia (16°S, 6000-4900 m above sea level, 2.4 km2), to investigate atmospheric forcing that controls seasonal variations in the mass balance and in meltwater discharge of glaciers in the outer tropics. Surface energy fluxes and melt rates were simulated for each 20 × 20m2 grid cell at an hourly resolution, for the hydrological year 1999-2000, using meteorological measurements in the ablation area. Model outputs were compared to measurements of meltwater discharge, snow cover extent, and albedo at two weather stations set up on the glacier. Changes in melt rate in three distinct seasons were related to snowfall and cloud radiative properties. During the dry season (May to August), the low melt rate was mainly caused by low long-wave emission of the cloudless thin atmosphere found at these high altitudes. From September to December, meltwater discharge increased to its annual maximum caused by an increase in solar radiation, which was close to its summer peak, as well as a decrease in glacier albedo. From January on, melt was reduced by snowfalls in the core wet season via the albedo effect but was maintained thanks to high long-wave emission from convective clouds. The frequent changes in snow cover throughout the long ablation season lead to large vertical mass balance gradients. Annual mass balance depends on the timing and length of the wet season, which interrupts the period of highest melt rates caused by solar radiation. © 2011 by the American Geophysical Union.