Natures wonders: under water caterpillar wonders (Introduction)

by David Turell , Tuesday, October 11, 2016, 00:48 (2964 days ago) @ David Turell

Certain pupas and/or caterpillars can spend hours to days under water and survive:-http://www.livescience.com/56411-goliath-worms-survive-drowning.html?utm_source=ls-newsletter&utm_medium=email&utm_campaign=20161010-ls-"Hefty, bright-green caterpillars sometimes called goliath worms are living up to their moniker: They are so tough, they can survive underwater for hours, scientists have found. 
   
"And during their pupa stage — encased in a chrysalis before transforming into adult moths — they can survive for days at a time without surfacing.-"Researchers discovered that the hardy caterpillars of Manduca sexta moths could recover after spending as much as 4 hours immersed in water. The pupae were even more resilient, emerging after a five-day soak and showing no long-term ill effects.-***-"Insects experiencing long dunks underwater use one of two mechanisms to survive and recover, Woods said.-"One technique involves the insect extracting oxygen from the surrounding water; that requires specialized body parts. Mayflies and damselflies, for example, have a type of gill that connects to the trachea and conveys dissolved oxygen in water into the insect's body, allowing them to breathe even when fully immersed.-"The other method involves sealing up the body and getting by without oxygen, a process known as anaerobic metabolism. But this can be risky, Woods said. This type of metabolism produces toxic byproducts, which, at high levels, can poison the insect.
"So usually insects can use anaerobic metabolism for finite periods of time," he said.-"To find out M. sexta's strategy for surviving underwater, the researchers immersed caterpillars and the more developed pupae. The caterpillars were able to recover after 4 hours underwater — not too shabby. But pupae were "the champs" at recovery, according to Woods. He and his colleagues found that the submerged pupae didn't draw upon dissolved oxygen, and relied on anaerobic metabolism to keep going when they were underwater, for as long as five days.-"In the absence of oxygen, a compound called lactate built up in the M. sexta pupae's cells. This could have had fatal consequences, but the scientists found that M. sexta was capable of quickly metabolizing, or breaking down, the lactate once they were removed from the water.-"But after spending a long time in water, a sudden reinfusion of life-giving oxygen doesn't necessarily mean that M. sexta's troubles are over.-"That big pulse of oxygen can generate what are called 'oxygen radicals' — basically toxic oxygen-based molecules that zip around and damage other molecules in cells," he told Live Science. "We found that Manduca had elevated metabolic rates well beyond the point when they had rid themselves of all the lactate — which we think means that they were still repairing other tissues," Woods said."-Comment: Again it is difficult to see how this developed in step by step evolution unless there was enough initial variation in the insects and the longest breath holders in floods survived and bit by bit descendent survivors developed the capacity.