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  Roaches hold their breath to stay alive
Australian scientists have discovered another reason why cockroaches might well inherit the earth after humans are long gone.

Animal physiologist Dr Craig White of the University of Queensland in Brisbane and colleagues report their findings in the Journal of Experimental Biology.

"Several decades ago, scientists discovered that some insects hold their breath," says White.

"But it's not been clear why they do this."

In the case of butterfly pupae and beetles it's for hours at a time, while cockroaches can hold their breath for five to seven minutes.

They do this by using a very efficient breathing system that uses air filled tubes, called trachea, to deliver oxygen directly to cells.

Oxygen flows in as required into the tracheal system through valves on the insect, called spiracles.

But, sometimes, they shut their spiracles and stop breathing.

One reason for this could be is that they are trying to stop too much oxygen from entering: too much oxygen can be toxic.

Another reason could be that closing spiracles helps build carbon dioxide, making it easier to expel.

Still another reason is that it helps regulate the insect's loss of water.

"The problem with having this tracheal system that delivers oxygen directly to the cells is that it also carries water vapour out of the cells," says White.

"The idea here is they close their spiracles when they have low requirement for oxygen, so then they don't let the water out."
Breathing study

To investigate this question White's student Natalie Schimpf examined cockroach breathing over a four-week period under different conditions of oxygen, carbon dioxide and humidity.

"Some were kept in dry air for four weeks, some were kept in very moist air for four weeks," says White.

The experiment confirmed the water loss hypothesis.

"In the dessicating environments the cockroaches open their spiracles for less time so they didn't lose as much water," says White.
Pesticides and climate change

White says the findings could explain how some cockroaches develop resistance to pesticides.

"There have been theories that the strains of cockroaches that are resistant to pesticides might hold their breath for longer, for example," he says.

White says it would be very interesting to study a wide range of resistant and non-resistant animals to see if breath-holding is a common resistance mechanism.

The findings also show cockroaches can change their respiratory environment to suit their environment.

While cockroaches generally like a bit of moisture, as climate change brings warmer and drier environments to many parts of the world, it seems this won't phase the roaches much.

"It suggests they will cope with that change," says White. "They are extraordinarily robust."
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