../Morning Post
Posted August 6, 2009
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Small Genome

Hummingbirds Powered by 'Light' DNA, Study Finds

Guelph - Hummingbirds have less DNA in their cells than other birds, allowing them to do all that energy-intensive hovering flight, according to new research by University of Guelph biologists.

Genome size, or the amount of genetic material in cells, is the smallest and least variable in hummingbirds when compared to that of other bird families, say integrative biology professor Ryan Gregory and master's student Chandler Andrews. Their study, co-authored by scientists at the University of California, Berkeley, and the University of New Mexico, appears in this week’s Proceedings of the Royal Society B.

Featherweight DNA in hummingbirds fits a theory saying that creatures with more high-powered metabolic demands have smaller genome sizes, said Gregory.

Small cells and small genomes, especially in red blood cells, have higher surface area compared to their volume and allow more efficient gas exchange. That's especially important for hummingbirds whose energy-intensive flight involves hovering, particularly at high elevations where the birds need to work harder to grab oxygen and maintain lift.

"This study reinforces the view that the amount of DNA, and not just the small fraction of the genome that encodes proteins, is linked in important ways with the biological features of animals," said Gregory. Last year, he published the largest-ever songbird study showing that more efficient flyers have smaller genome sizes.

For the new study, the researchers looked at DNA in 37 hummingbird species in Peru and New Mexico. The smallest species weighed almost 2.5 grams (about as much as a penny) on average and the largest about 21 grams. Their genomes are about 40 per cent smaller than average for birds and less than one-third the size of the human genome.

There were small variations in genome size among the hummingbirds studied. That might have less to do with flight and more with habitat, said Gregory. Species living in small groups high in the tropical forest have larger genomes, although he says more study is needed to figure out why.

In general, Gregory said more energy-intensive flight has likely led to smaller genome sizes in birds and particularly within hummingbirds.

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