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Low oxygen triggers moth molt

Public release date: 22-Aug-2011 [ | E-mail | Share ] Contact: Ashley Yeagerashley.yeager@duke.edu919-681-8057Duke University DURHAM, N.C. — A new explanation for one of nature’s most mysterious processes, the transformation of caterpillars into moths or butterflies, might best be described as breathless. The research shows that a baby moth’s respiratory system is fixed in size at each stage of development, which limits its oxygen intake. Sensing it is low on oxygen apparently signals to the insect that it cannot continue to grow without proceeding to the next stage of its development, by molting. Caterpillars molt four to five times before morphing into an adult as a moth or butterfly. Duke University biologist Fred Nijhout knew from earlier work that tobacco hornworm caterpillars, or Manduca sexta, only start a molt when they reach a critical weight — exactly 4.8 times more than their weight immediately after they last shed their exoskeleton. Still, he and other scientists didn’t understand how the caterpillars sensed they had reached that specific size. In the new study, Nijhout and his graduate student, Viviane Callier, measured the size of the caterpillar’s respiratory system. They found that the insect’s tracheal tubing is fixed in size at each stage of its larval life. Other parts of the caterpillar’s body can grow, but not the respiratory tubing. As a result, the insect eventually begins to suffocate. The only way it can continue to mature is to shed the old tubing for newer, longer ones. This is the first time scientists have figured out a factor

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