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氧气浓度造就飞行类昆虫前世今生

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小编摘要:据研究发现,上百万年前巨型飞行昆虫的出现和灭绝,与它们的水生幼虫能获取到氧的多少有关。

导读:科学家研究发现,3亿年前巨型飞行类昆虫的存在,是大气中高浓度氧对其幼虫的作用。像巨型蜻蜓翼展能接近一米,是幼虫受高浓度氧的影响。后来,随着大气变化,氧浓度降低,更大物种的幼虫便没能有足够能量存活下来。这项发现,从幼虫角度出发,为研究巨型生物历史提供了新思路。

                           Gigantic insects including a dragonfly with a wingspan of 75cm died out millions of years ago due to a lack of oxygen which had made them giant in the first place

The emergence and decline of gigantic flying insects millions of years ago may have been linked to the amount of oxygen available to their water-breathing young, according to a study.

Scientists studying the smaller modern-day descendants of the huge creatures, which included dragonflies with wingspans of almost a metre, believe they have solved a question which has puzzled experts for more than 100 years by looking at their larvae, which live in water.

They believe that larvae 300million years ago took advantage of the higher oxygen levels available, using it to help fuel their growth to the size shown in fossilised remains found by palaeontologists today.

When the climate later changed and the oxygen level dropped, the larger species' larvae could not take in enough of the gas to survive and the species went extinct, leaving only their smaller relatives alive.

Dr David Bilton, of Plymouth University's School of Marine Science and Engineering, who carried out the research, said: 'In prehistoric times, higher levels of oxygen may have favoured the evolution of giant insects largely through their effects on larvae, and it is perhaps no accident that many extinct giants had aquatic juvenile stages.'

In their paper, published in the Public Library of Science, Dr Bilton and co-author Dr Wilco Verberk show that aquatic insect larvae are more sensitive to fluctuations in oxygen levels than the air-breathing land-based adults.

Though a link between oxygen levels and giant insects has been suggested before, no one has provided firm evidence of how they are linked.

The research, which looked at the stonefly (Dinocras cephalotes), said aquatic larvae, such as those of dragonflies, stoneflies and mayflies, extract their oxygen directly from the water, where far less is available than in air.

The larvae were also less efficient at extracting oxygen from the water than their air-breathing elders.

This, the scientists suggest, would make them more sensitive to changes in available oxygen and therefore the gas's role in shaping insect body size may be particularly important in aquatic larvae, setting an upper size limit.

Giant insects have featured largely in science-fiction stories involving the far distant past, with dragonflies featuring in Michael Crichton's novel Jurassic Park, which spawned the multi-million dollar film franchise.

Scientists believe that the creatures, with wingspans of up to 75cm recorded, lived during the Carboniferous period from about 354 to 290 million years ago.

Dr Verberk added: 'To date, attempts to understand insect gigantism in the past have been mainly approached from the perspective of (fossilised) terrestrial adults.'

'Our work suggests that approaching the problem of historical gigantism from a larval perspective may shed new light on the way in which oxygen sets insect body size limits.'

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2011-08-05 16:51 编辑:jeannn
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