The Color of Evolution: How One Fish Became Two Fish
Ever since Darwin discovered that species can evolve, scientists have wondered how new species form. Answering this question is the key to understanding the diversity of all of life. A group of colorful fishes in Africa's Lake Victoria have been the focus of scientific efforts to unravel how new species form. This lake contains more than 500 species of cichlids, which play a leading role because of their rapid speciation and remarkable diversity. Still, the mechanisms involved in the rapid appearance of new cichlid species have remained elusive to scientists.
Now a new study highlighted on the cover of the journal Nature (October 1, 2008) suggests that species of Lake Victorian cichlids became new species after changes in how they see led to changes in the mates that they selected. The group of biologists, which is led by Ole Seehausen of the University of Bern in Switzerland, and includes Karen Carleton of the University of Maryland, say that the phenomenon provides evidence that differences in sensory perception contribute to the development of new species.
For many years, scientists have linked evolution to the environment and suggested that new species arise when populations become geographically isolated from one another, thus forcing them to adapt differently. The idea that organisms living right next to each other can separate into two new species has been proposed, but difficult to prove.
The waters of Lake Victoria, which borders Uganda, Kenya, and Tanzania, are murky and red light penetrates deeper than blue light. In the shallow waters, the male fish tend to be green to blue, and in the deeper waters, the male fish are marked by a brilliant red. "These fish specialized to different microhabitats," Carleton explains, "which in this case is different depths. The visual system then specialized to the light environment at these depths and the mating colors shifted to match. Once this happened, these two groups no longer interbred and so became new species."
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Fossilised shrimp show earliest group behaviour
The conga was the world's first dance, it seems. A newly discovered caravan of crustaceans from half a billion years ago shows that group behaviour evolved not long after animals themselves.
Palaeontologists led by Hou Xian-Guang, of Yunnan University, China, discovered fossilised chains of up to 20 crustaceans linked head-to-toe, the earliest record of any collective animal behaviour and perhaps an adaptation to a migratory ocean lifestyle.
"It's showing that, 525 million years ago, we've got really quite sophisticated and potentially complex interaction between different animals," says Derek Siveter, of the University of Oxford, who analysed the fossil along with colleagues at the University of Leicester, UK.
They concluded that the undulating procession of ancient arthropods, each about 2 centimetres long, represents more than a quirk of fossilisation. Though none of their arms, legs or antennae survived a half billion years in stone, the animals probably interlocked appendages to stay together.
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How Brachiosaurs Got So Huge
Brachiosaurs and other long-necked giants of the dinosaur world weighed as much as 10 African elephants. Researchers now think they know why the tubby vegetarian beasts got so big: They swallowed high-energy foods whole.
Their small heads helped, too, by allowing those long necks to reach nutritious leaves high up in the trees.
With body lengths of more than 131 feet (40 m) and heights of 56 feet (17 m), sauropods dwarfed meat-eating dinosaurs and even the largest land mammals ever. Sauropods appeared on the scene about 210 million years ago in the Late Triassic and dominated Earth's ecosystems for more than 100 million years from the Middle Jurassic to the end of the Cretaceous.
P. Martin Sander, a paleontologist at the University of Bonn in Germany, and Marcus Clauss of the University of Zurich propose how the plant-eaters could have reached such super sizes and thrive for so long.