have a role, do one's part, work on, be bad for, cut down
A dragonfly barely an inch and a half long appears to be the animal world's most productive long-distance traveler—flying thousands of miles over oceans as it migrates from continent to continent—according to newly published research.
Biologists who led the study say the evidence is in the genes. They found that populations of this dragonfly, called Pantala flavescens, in Texas, eastern Canada, Japan, Korea, India, and South America, have such similar genes that there is only one likely explanation. Apparently—somehow—these insects are traveling distances that are extraordinarily long for their small size, breeding (繁殖) with each other, and creating the common worldwide gene pool.
But how do insects from different continents manage to meet and hook up? Ware says it appears to be the way their bodies have evolved. "These dragonflies have adaptations such as increased surface areas on their wings that enable them to use the wind to carry them. "
Dragonflies, in fact, have already been observed crossing the Indian Ocean from Asia to Africa. "They are following the weather," says Daniel Troast, who analyzed the DNA samples in Ware's lab. "They're going from India where it's the dry season to Africa where it's the wet season, and apparently they do it once a year. "
Wetness is a must for Pantala flavescens to reproduce, and that, says Ware, is why these insects would be driven to even attempt such a dangerous trip, which she calls "a kind of suicide". The species depends on it. While many will die on the route, as long as enough of them make it, the species survives.
For the moment, the details of this extraordinary insect travel are a best educated guess. Much more work is needed to bring many loose ends together. Ware and Troast hope that scientists can work on plotting those routes.
In 1994, The Brazilian photographer Salgado went back to his homeland in Minas Gerais, Brazil. He was1 to see the land run by his family. The thick forest there was once a paradise (乐园) for him and his friends, bringing them2 memories.
To his horror, he saw a totally different3. Only 0. 5% of the land was covered with trees. "The land was as sick as a serious patient—everything was4 due to deforestation (滥伐森林)," Salgado said5 during a meeting on climate change in Paris.
Salgado6that he should do something about it. Then he 7the bold idea of replanting trees on the land, which beyond his expectation, received8 from his wife and relatives. Soon the whole family 9 and the results were remarkable. 10, the land was changing: it was carpeted with green trees again and some of the insects, birds and animals living in the land before11. The land has been brought back to life. The12 family's hard work also impressed people around them. They13 cutting down trees and began to protect the environment.
"The work over the years is quite difficult but well worth the14 and I think every little bit of work15," said Salgado. Therefore, everyone should play a part in protecting the environment.
