Strange tale of the lizard’s breath

The Star Malaysia - Star2 - - SCIENCE -

AIR flows through lizard lungs in one di­rec­tion, a find­ing that may prompt a re­think about how some species evolved fol­low­ing Earth’s big­gest mass ex­tinc­tion, a new study says.

Hu­mans and most other an­i­mals in con­trast have a so-called “tidal” or two-way breath­ing sys­tem.

Air is drawn into the lungs un­til it reaches a dead end – bunches of cells called alve­oli. There, oxy­gen is drawn into the blood­stream and ex­changed for carbon diox­ide, which is then breathed out with the used air.

Birds, though, are a no­table ex­cep­tion to this.

Their breath­ing is pre­dom­i­nantly a one-way flow into the lungs. The air en­ters the trachea, or wind­pipe, flows through the lung in one di­rec­tion and then ex­its the way it came in.

This un­usual pat­tern of breath­ing has raised much de­bate among bi­ol­o­gists.

One the­ory is that a one-way flow is a highly ef­fi­cient way of pro­vid­ing oxy­gen for stren­u­ous ac­tiv­ity: it helps birds cope with the ex­er­tion of fly­ing and deal­ing with thin­ner con­cen­tra­tions of oxy­gen at al­ti­tude.

But, sur­pris­ingly, lizards – a sleepy group of land-lov­ing an­i­mals – can also be counted as mem­bers of the club, ac­cord­ing to the new probe.

Univer­sity of Utah bi­ol­o­gist CG Farmer led a team that car­ried out 3D scans of the lungs of African mon­i­tor lizards ( Varanus ex­an­the­mati­cus) and then im­planted flow me­tres in five of the an­i­mals to see how the air moved.

They also pumped air into the lungs of 10 dead lizards, and then wa­ter, laden with sun­flower pollen as a tracer. Th­ese, too, showed a uni­lat­eral flow.

The investigators found that air en­ters the lizards’ trachea and then splits into two air­ways, one for each lung.

It then winds its way through a se­ries of cham­bers in each lung, pass­ing through per­fo­rated walls, be­fore dou­bling back. The used gas heads out through the trachea. As with birds, there is some “tidal” flow, but not much.

A sim­i­lar one-way flow also ap­pears to ex­ist among Amer­i­can al­li­ga­tors, help­ing them quite lit­er­ally to hold their breath, whether they are un­der wa­ter or not, Farmer said in a phone in­ter­view.

If so, some of the think­ing about uni­di­rec­tional breath­ing – that it helps to sus­tain high me­tab­o­lism – has to be scrapped.

“I think it’s prob­a­bly not an adap­ta­tion al­low­ing an an­i­mal to be ac­tive,” Farmer said.

“In fact, (it’s likely to be) an adap­ta­tion to al­low them to sit qui­etly for long pe­ri­ods of time with­out mov­ing, with­out breath­ing,” she said. – AFP

air flows through lizard lungs in one di­rec­tion, a find­ing that may prompt a re­think about how some species evolved fol­low­ing earth’s big­gest mass ex­tinc­tion. — aFP photo

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