How Did Flowering Plants Evolve to Dominate Earth?

To Charles Darwin it was an 'abominable mystery' and it is a question which has continued to vex evolutionists to this day: when did flowering plants evolve and how did they come to dominate plant life on earth? A new study in Ecology Letters reveals the evolutionary trigger which led to early flowering plants gaining a major competitive advantage over rival species, leading to their subsequent boom and abundance.

The study, by Dr Tim Brodribb and Dr Taylor Field of the University of Tasmania and University of Tennessee, used plant physiology to reveal how flowering plants, including crops, were able to dominate land by evolving more efficient hydraulics, or 'leaf plumbing', to increase rates of photosynthesis.

"Flowering plants are the most abundant and ecologically successful group of plants on earth," said Brodribb. "One reason for this dominance is the relatively high photosynthetic capacity of their leaves, but when and how this increased photosynthetic capacity evolved has been a mystery."

Using measurements of leaf vein density and a linked hydraulic-photosynthesis model, Brodribb and Field reconstructed the evolution of leaf hydraulic capacity in seed plants. Their results revealed that an evolutionary transformation in the plumbing of angiosperm leaves pushed photosynthetic capacity to new heights.

The reason for the success of this evolutionary step is that under relatively low atmospheric C0₂ conditions, like those existing at present, water transport efficiency and photosynthetic performance are tightly linked. Therefore adaptations that increase water transport will enhance maximum photosynthesis, exerting substantial evolutionary leverage over competing species.

The evolution of dense leaf venation in flowering plants, around 140-100 million years ago, was an event with profound significance for the continued evolution of flowering plants. This step provided a 'cretaceous productivity stimulus package' which reverberated across the biosphere and led to these plants playing the fundamental role in the biological and atmospheric functions of the earth.

"Without this hydraulic system we predict leaf photosynthesis would be two-fold lower then present," concludes Brodribb. "So it is significant to note that without this evolutionary step land plants would not have the physical capacity to drive the high productivity that underpins modern terrestrial biology and human civilisation."

Courtesy: ScienceDaily

Naked Mole Rats May Hold Clues to Surviving Stroke

Blind, nearly hairless, and looking something like toothy, plump, pink fingers, naked mole rats may rank among nature's most maligned creatures, but their unusual physiology endears them to scientists.

Two University of Illinois at Chicago researchers report in the Dec. 9 issue of NeuroReport (now online) that adult naked mole rat brain tissue can withstand extreme hypoxia, or oxygen deprivation, for periods exceeding a half-hour -- much longer than brain tissue from other mammals.

The findings may yield clues for better treatment of brain injuries associated with heart attack, stroke and accidents where the brain is starved of vital oxygen.

John Larson, associate professor of physiology in psychiatry, and Thomas Park, professor of biological sciences, studied African naked mole rats -- small rodents that live about six feet underground in big colonies of up to 300 members. The living is tight and the breathing even worse, with the limited air supply high in carbon dioxide and low in oxygen.

The air they breathe is so foul it would be fatal or lead to irreversible brain damage in any other mammal, Larson and Park said.

But naked mole rats studied were found to show systemic hypoxia adaptations, such as in the lungs and blood, as well as neuron adaptations that allow brain cells to function at oxygen and carbon dioxide levels that other mammals cannot tolerate.

"In the most extreme cases, naked mole rat neurons maintain function more than six times longer than mouse neurons after the onset of oxygen deprivation," said Larson.

"We also find it very intriguing that naked mole rat neurons exhibit some electrophysiological properties that suggest that neurons in these animals retain immature characteristics."

All mammal fetuses live in a low-oxygen environment in the womb, and human infants continue to show brain resistance to oxygen deprivation for a brief time into early childhood. But naked mole rats, unlike other mammals, retain this ability into adulthood.

"We believe that the extreme resistance to oxygen deprivation is a result of evolutionary adaptations for surviving in a chronically low-oxygen environment," said Park.

"The trick now will be to learn how naked mole rats have been able to retain infant-like brain protection from low oxygen, so we can use this information to help people who experience temporary loss of oxygen to the brain in situations like heart attacks, stroke or drowning," he said.

Larson said study of the naked mole rat's brain may yield clues for learning the mechanisms that allow longer neuronal survival after such accidents or medical emergencies, which may suggest ways to avoid permanent human brain damage.

Courtesy: ScienceDaily