Legge di Kleiber

How evolution shapes the geometries of life

Why does a mouse's heart beat about the same number of times in its lifetime as an elephant's, although the mouse lives about a year, while an elephant sees 70 winters come and go? 

Why do small plants and animals mature faster than large ones? 

Why has nature chosen such radically different forms as the loose-limbed beauty of a flowering tree and the fearful symmetry of a tiger? New research suggests that the shapes of both plants and animals evolved in response to the same mathematical and physical principles. 

By working through the logic underlying Kleiber’s Law (metabolism equals mass to the three-quarter power) and applying it separately to the geometry of plants and animals, researchers were able to show that plants and animals display equivalent energy efficiencies [Credit: Loretta Kuo] 

These questions have puzzled life scientists since ancient times. Now an interdisciplinary team of researchers from the University of Maryland and the University of Padua in Italy propose a thought-provoking answer based on a famous mathematical formula that has been accepted as true for generations, but never fully understood. In a paper published the week of Feb. 17, 2014 in the Proceedings of the National Academy of Sciences, the team offers a re-thinking of the formula known as Kleiber's Law.

 Seeing this formula as a mathematical expression of an evolutionary fact, the team suggests that plants' and animals' widely different forms evolved in parallel, as ideal ways to solve the problem of how to use energy efficiently. 
If you studied biology in high school or college, odds are you memorized Kleiber's Law: metabolism equals mass to the three-quarter power. This formula, one of the few widely held tenets in biology, shows that as living things get larger, their metabolisms and their life spans increase at predictable rates. Named after the Swiss biologist Max Kleiber who formulated it in the 1930s, the law fits observations on everything from animals' energy intake to the number of young they bear. 

It's used to calculate the correct human dosage of a medicine tested on mice, among many other things. But why does Kleiber's Law hold true? Generations of scientists have hunted unsuccessfully for a simple, convincing explanation. In this new paper, the researchers propose that the shapes of both plants and animals evolved in response to the same mathematical and physical principles. By working through the logic underlying Kleiber's mathematical formula, and applying it separately to the geometry of plants and animals, the team was able to explain decades worth of real-world observations. "Plant and animal geometries have evolved more or less in parallel," said UMD botanist Todd Cooke. "The earliest plants and animals had simple and quite different bodies, but natural selection has acted on the two groups so the geometries of modern trees and animals are, remarkably, displaying equivalent energy efficiencies. They are both equally fit. And that is what Kleiber's Law is showing us." Picture two organisms: a tree and a tiger. In evolutionary terms, the tree has the easier task: convert sunlight to energy and move it within a body that more or less stays put. To make that task as efficient as possible, the tree has evolved a branching shape with many surfaces -- its leaves. "The tree's surface area and the volume of space it occupies are nearly the same," said physicist Jayanth Banavar, dean of the UMD College of Computer, Mathematical, and Natural Sciences. "The tree's nutrients flow at a constant speed, regardless of its size." With these variables, the team calculated the relationship between the mass of different tree species and their metabolisms, and found that the relationship conformed to Kleiber's Law. To nourish its mass, an animal needs fuel. Burning that fuel generates heat. The animal has to find a way to get rid of excess body heat. The obvious way is surface cooling. But because the tiger's surface area is proportionally smaller than its mass, the surface is not up to the task. The creature's hide would get blazing hot, and its coat might burst into flames. So as animals get larger in size, their metabolism must increase at a slower rate than their volume, or they would not be able to get rid of the excess heat. If the surface area were the only thing that mattered, an animal's metabolism would increase as its size increased, at the rate of its mass to the two-thirds power. But Kleiber's Law, backed by many sets of observations, says the actual rate is mass to the three-quarters power. Clearly there's a missing factor, and scientists have pored over the data in an attempt to find out what it is. Some have proposed that the missing part of the equation has to do with the space occupied by internal organs. Others have focused on the fractal, or branching, form that is common to tree limbs and animals' blood vessels, but added in new assumptions about the volume of fluids contained in those fractal networks. The UMD and University of Padua researchers argue a crucial variable has been overlooked: the speed at which nutrients are carried throughout the animals' bodies and heat is carried away. So the team members calculated the rate at which animals' hearts pump blood and found that the velocity of blood flow was equal to the animals' mass to the one-twelfth power. "The information was there all along, but its significance had been overlooked," said hydrologist Andrea Rinaldo of Italy's University of Padua and Switzerland's Ecole Polytechnique Federale. "Animals need to adjust the flow of nutrients and heat as their mass changes to maintain the greatest possible energy efficiency. That is why animals need a pump -- a heart -- and trees do not." Plugging that information into their equation, the researchers found they had attained a complete explanation for Kleiber's Law. "An elegant answer sometimes is the right one, and there's an elegance to this in the sense that it uses very simple geometric arguments," said physicist Amos Maritan of the University of Padua. "It doesn't call for any specialized structures. It has very few preconditions. You have these two lineages, plants and animals, that are very different and they arrive at the same conclusion. That is what's called convergent evolution, and the stunning result is that it's being driven by the underlying physics and the underlying math." 

Source: University of Maryland [February 17, 2014]

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BARRIERA CORALLINA della GROENLANDIA

Coral reef discovered off Greenland 



By sheer coincidence, Canadian researchers have discovered a reef of living cold-water corals in southern Greenland. PhD student Helle Jørgensbye from DTU in Denmark has been investigating the reef further 

Coral from the newly discovered reef off Greenland [Credit: Bedford Institute of Oceanography] 

The first ever Greenlandic reef is located in southwest Greenland and was formed by cold-water corals with hard limestone skeletons. There are several species of coral in Greenland, but this is the first time that an actual reef has been found. In the tropics, reefs are popular tourist destination for divers, but there is little prospect of Greenland becoming a similar diving hotspot. The newly discovered living reef is located off Cape Desolation south of Ivittuut, and lies at a depth of 900 metres in a spot with very strong currents, making it difficult to reach. This also means that so far little is known about the reef itself and what lives on it The reef was discovered by accident when a Canadian research vessel needed to take some water samples. When the ship sent the measuring instruments down to a depth of 900 metres, they came back up completely smashed. Fortunately there were several pieces of broken coral branches on the instrument that showed what was responsible. "At first the researchers were swearing and cursing at the smashed equipment and were just about to throw the pieces of coral back into the sea, when luckily they realized what they were holding," says PhD student Helle Jørgensbye, DTU Aqua, who does research into life at the bottom of the west Greenland waters. The first photos Another Canadian research vessel returned to the site last fall to try and lower a camera down onto the reef to explore it close up. The coral reef is on the continental shelf itself where it is very steep and where there are strong currents. "We got some photos eventually, although we almost lost them at the bottom of the ocean as the camera got stuck fast somewhere down in the depths. Luckily we managed to get it loose again and back up to the surface," says Helle Jørgensbye. "It's been known for many years that coral reefs have existed in Norway and Iceland and there is a lot of research on the Norwegian reefs, but not a great deal is known about Greenland. In Norway, the reefs grow up to 30 metres high and several kilometres long. The great Norwegian reefs are over 8,000 years old, which means that they probably started to grow after the ice disappeared after the last ice age. The Greenlandic reef is probably smaller, and we still don't know how old it is," says Helle Jørgensbye, expressing the hope that at some point this will be investigated more closely. According to Helle Jørgensbye, finding a coral reef in southern Greenland was not entirely unexpected: "There are coral reefs in the countries around Greenland and the effect of the Gulf Stream, which reaches the west coast, means that the sea temperature get up to about 4 degrees, which is warm enough for corals to thrive. In addition to the, for Greenland, comparatively warm temperature, a coral reef also needs strong currents. Both these conditions can be found in southern Greenland," she says. Coral reefs are important areas for fish because it provides masses of food and lots of hiding places for fish fry. The Greenlandic reef is formed from Lophelia stoney corals. Other species of coral are also found in many parts of the west coast. However, they are all 'stand-alone' corals and do not form reefs. The identification of the Lophelia specimen was carried out by Professor Ole Tendal from Denmark's Natural History Museum. 
Cold Water Corals 
Normally, coral reefs are associated with the tropics, but they are also found in cold waters. While the tropical coral reefs depend on light to survive, cold-water coral reefs live in total darkness, at depths the sun's rays never penetrate. Nevertheless, they have many colourful residents and many different kinds of organisms living in them. Coral reefs are built up of thousands of small coral animals that live in a large colony which forms a common limestone skeleton. While hot water corals obtain some of the energy they need to grow from the light-dependent green algae which live in the corals, cold water coral get all their nourishment from small animals, which they catch. Thus, they are not dependent on light and can live in very deep water 

Source: Technical University of Denmark (DTU) [January 28, 2014]

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La VI estinzione di massa: 2250, causata dall'Uomo.

C'è forse un po' di allarmismo. 

Ma sostanzialmente è vero che l'Uomo si sta comportando con la Terra come un agente infettivo troppo avido nei confronti del proprio ospite...

Un agente patogeno non troppo aggressivo (si pensi all'influenza) riesce infatti a vivere bene a spese della propria vittima, rispettandone le necessità di riproduzione e di sopravvivenza, in modo che ambedue possano coesistere a lungo nell'ambiente.

Un agente troppo aggressivo, invece, distrugge troppo efficacemente l'ospite e si estingue presto anch'egli (basta pensare ad Ebola). 

Humans will have

wiped out 75%

of species by 2250 

Humans will wipe out 75% of the species on Earth in around 240 years, a scientist has said. Mike Coffin, a marine geophysicist from the University of Tasmania, has said mankind will cause a mass extinction event between 240 and 500 years from now, which will see most species on the planet going extinct. 


According to Australia Broadcasting Corporation (ABC News), Coffin told a conference in Hobart that humans will cause the sixth mass extinction event to face the planet. The last five mass extinctions, which have taken place over the last 550 million years, were caused by asteroids hitting Earth, climate fluctuations and volcanic eruptions. The most devastating event took place around 250 million years ago. In the Permian event, 96% of species were lost following the combination of a massive volcanic eruption in Siberia, global warming and deep sea anoxic waters. If 75% of Earth's species were wiped out, as Coffin predicts, the loss would be similar to the best known extinction event – the Cretaceous–Paleogene extinction event – when a massive asteroid wiped out about three quarters of all plant and animal life on Earth, including all the dinosaurs. "We're on a trajectory to reach the 75% level sometime between 240 and 2,000 years from now," he told ABC. "Based on all threatened species as defined by the International Union for the Conservation of Nature ... assuming all of those threatened species become extinct then we would reach mass extinction somewhere between 240 and 540 years from now." He estimates that there are around 8.7 million species on Earth today, excluding the creatures and plants yet to be discovered. "We've only [discovered] about 15 per cent. So there is still 85 per cent that are yet to be discovered and or described." 

Discussing mankind's role in future mass extinction, he said "Homo sapiens have been around for 200,000 years - that's the length of our reign. The dinosaurs were around for 165 million years, so we're just a little blip on the geological time-scale. We haven't been around very long but we seem to be very good at driving a mass extinction ourselves." Animals that might survive the event include smaller ones that can breed quickly, such as cockroaches. "Species like us that don't reproduce until we're in our teens at earliest, with long gestation periods and that take a long time to evolve or adapt - big mammals - we're most vulnerable." However, Coffin also said he does not think mankind will kill all life on Earth: "Prior to the explosion of multi-cellular life 540 million years ago there were at least two episodes where the total surface of the Earth froze over - we call that a Snowball Earth. "There was single cell life back then, and even though the entire planet froze over some of that life survived. That's why we are here today." 

Author:  Hannah Osborne } Source: International Business Times [January 14, 2014]

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Pro e contro del resuscitare animali estinti

The pros and cons of resurrecting

extinct animals


 Scientists from across the world have “scanned the horizon” in order to identify potentially significant medium and long-term threats to conservation efforts. Thylacine, or Tasmanian tiger Credit: E.J. Keller Baker/WikiCommons] Resurrection of several extinct species, the increasingly accelerated loss of wild rhinoceroses and a disastrous financial response to unburnable carbon are just some future global conservation issues flagged up in this year’s Horizon Scan, recently published in Trends in Ecology and Evolution. Professor William Sutherland and Dr Mark Spalding are amongst the 18 scientists who took part in this year’s Horizon Scan, seeking to identify potential future conservation issues in order to reduce the “probability of sudden confrontation with major social or environmental changes”. One such plausible issue is the resurrection or re-construction of extinct species, such as the woolly mammoth, passenger pigeon or the thylacine (a carnivorous marsupial). However, though there may be many benefits to the restoration of these animals, such a high-profile project could lead to attention and resources being diverted from attempts to thwart current threats to non-extinct species’ survival. Professor Sutherland said ‘There has been discussion of this idea for some time but it is now looking more practical and the idea is being taken seriously. A key issues is whether this is really a conservation priority’. Though the last woolly mammoth died around 4000 years ago, methods such as back-breeding, cloning and genetic engineering may lead to their resurrection. Not only could these extinct animals, and others such as the thylacine and the passenger pigeon, be re-constructed and returned to their native environments, they could potentially be used to “provide tools for outreach and education”. However, though this would be a conservational triumph, it could also hamper efforts to protect animals that are currently facing extinction, as both attention and resources would be diverted from preserving existing species and their habitats. Furthermore, there has not been any investigation into the “viability, ethics and safety of releasing resurrected species”, nor the effect their presence may have on indigenous flora and fauna. Another potential conservational issue identified by the Horizon Scan further highlights the problems facing species today. The loss of wild rhinoceroses and elephants is set to reaccelerate within the next few years, partially stimulated by a growing desire for ivory and horn. In 2013, it is estimated that over 600 rhinoceroses were poached for their horn in South Africa alone, out of a total global population of less than 26,000. Though an increased human population and proximity to growing infrastructure is partially responsible, organised crime syndicates and intensive hunting carry the weight of the blame. In the Asian countries that use it, rhinoceros horn is more expensive than gold. Demand for the precious horn is ever increasing, resulting in elevated levels of poaching. If attention and resources are diverted from the protection of these majestic animals, we may have yet more candidates for resurrection in the future. Altogether, this group of scientists identified the top 15 potential conservation issues (out of an initial group of 81 issues). In addition to the above topics, extensive land loss in southeast Asia from subsidence of peatlands, carbon solar cells as an alternative source of renewable energy, and an emerging fungal disease amongst snakes, have also been voted as plausible threats that need to be stopped before they can be realised. 

Source: University of Cambridge [December 24, 2013]
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Madre di tutti i profumi

Su una rivista botanica Finnica, compare la descrizione di una crucifera (come sono il cavolo, la senape ed il radicchio) che sarebbe la madre delle piante già usate nell'antica industria cosmetica: è la Reseda Minoica, pianta ormai rara, che corre il rischio di estinzione. Già abbiamo perso il silphium: speriamo di non dovere rimpiangere altre essenze rare...

Experts discover the 

mother of Roman perfumes 

on Mediterranean coast

Researchers at the Pablo de Olavide University in Seville have described a new plant in the eastern Mediterranean, growing mainly near the coast. The importance of this discovery is that the plant is the maternal ancestor of a species of hybrid origin, Reseda odorata, used since Roman times due to the fragrance of its flowers, and whose essence was used in the ancient cosmetics industry.

Researchers at the Pablo de Olavide University in Seville have described a new plant in the eastern Mediterranean, growing mainly near the coast. The importance of this discovery is that the plant is the maternal ancestor of a species of hybrid origin, Reseda odorata, used since Roman times due to the fragrance of its flowers, and whose essence was used in the ancient cosmetics industry [Credit: Santiago Martin Bravo et. al.]

An article published in the journal Annales Botanici Fennici describes a new species of flowering plant, Reseda minoica, from the eastern Mediterranean region, more specifically from Crete (Gavdos Island, Greek's southernmost island), Cyprus and Southern Turkey. "This species belongs to the genus Reseda of the Resedaceae family, related to the Cruciferae -- which includes plants such as cabbage, mustard and radish -- and grows on limestone substrates in scrubland near the coast," Santiago Martin Bravo, co-author of the study and Botanical researcher at the Pablo de Olavide University in Seville (UPO), explains.

The plant is included in section Phyteuma of Reseda genus, a taxonomically complex group mostly containing narrow endemics from the western or eastern Mediterranean region, areas considered to be of critical importance in the diversification of Mediterranean flora.

"Until now this plant has been confused with related species such as R. odorata, R. orientalis and R. balansae," the research adds. Reseda minoica can be distinguished from these other species by its lower number of stamens, seed size and petal colour.

According to Pedro Jimenez Mejias, the other co-author of the study and also a researcher at UPO, "the importance of this discovery is that Reseda minoica is the maternal ancestor of a cultivated species of hybrid origin, Reseda odorata, used since Roman times due to the fragrance of its flowers, and whose essence was used in the ancient cosmetics industry. The location of one of the parts of its origin (the mother species), provides information about the evolutionary mechanisms which produce species which are later useful to humankind."

Moreover, the scientists believe that the plant is "at present rare," and could require protection so that it does not become extinct. "If this were to happen, we would lose part of the Mediterranean's plant genetic resources, with a potential consequent loss for humankind in terms of use and opportunity," Jimenez notes.

In any case, since the species is a recent discovery, it is possible that botanists from areas where the plant grows will begin to search and discover it in other places.

Two other new species in Africa

The two researchers were also part of the recent discovery of two other new African species belonging to the genus Carex of the Cyperaceae family, which includes species such as the tiger nut and papyrus. One of these, Carex rainbowii, has been found in forests of the Drakensberg mountain range, in the KwaZulu-Natal region in eastern South Africa. The other, Carex modesti, is only known to exist at the edges of streams and peat bogs in a very localized area of the mountains of southern Tanzania.

The description of both species is a good example of the significant amount of biodiversity that may remain undiscovered, especially in remote areas of the planet, including in groups of living things well-known a priori such as plants and flowers.

Source: Plataforma SINC [October 09, 2013]