進(jìn)入英語學(xué)習(xí)論壇下載音頻

Scientists said on Tuesday that they had discovered the world's first hybrid sharks in Australian waters, a potential sign the predators were adapting to cope with climate change.

The mating of the local Australian black-tip shark with its global counterpart, the common black-tip, was an unprecedented discovery with implications for the entire shark world, said lead researcher Jess Morgan.

Morgan, from the University of Queensland, said that hybrid sharks have never been seen before.

"This is evolution in action," she said.

Colin Simpfendorfer, a partner in Morgan's research from James Cook University, said initial studies suggested the hybrid species was relatively robust, with a number of generations discovered across 57 specimens.

The find was made during cataloguing work off Australia's east coast when Morgan said genetic testing showed certain sharks to be one species when physically they looked to be another.

The Australian black-tip is slightly smaller than its common cousin and can only live in tropical waters, but its hybrid offspring have been found 2,000 kilometers down the coast, in cooler seas.

It means the Australian black-tip could be adapting to ensure its survival as sea temperatures change because of global warming.

Morgan explained that "If it hybridizes with the common species it can effectively shift its range further south into cooler waters, so the effect of this hybridizing is a range expansion."

"It's enabled a species restricted to the tropics to move into temperate waters."

Climate change and human fishing are some of the potential triggers being investigated by the team, with further genetic mapping also planned to examine whether it was an ancient process just discovered or a more recent phenomenon.

If the hybrid was found to be stronger than its parent species - a literal survival of the fittest -Simpfendorfer said it may eventually outlast its so-called pure-bred predecessors.

The hybrids were abundant, accounting for up to 20 percent of black-tip populations in some areas, but Morgan said that didn't appear to be at the expense of their single-breed parents, adding to the mystery.

Simpfendorfer said the study could challenge traditional ideas of how sharks had and were continuing to evolve.

Questions:

1. What species of sharks were the hybrids a combination of?

2. How was the discovery made?

3. What percentage of the black-tip population were hybrids?

Answers:

1. Australian black-tip shark and common black-tip.

2. During cataloguing work.

3. Up to 20 percent.

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About the broadcaster:

Emily Cheng is an editor at China Daily. She was born in Sydney, Australia and graduated from the University of Sydney with a degree in Media, English Literature and Politics. She has worked in the media industry since starting university and this is the third time she has settled abroad - she interned with a magazine in Hong Kong 2007 and studied at the University of Leeds in 2009.