How Hummingbirds Evolved to Thrive In High Altitudes

Hummingbirds have long been admired for their striking jewel-like plumage and minute size. With over 356 recognized species, these dainty creatures are found all the way from Alaska to the southernmost part of South America. And though they are the smallest members of the avian community, they have the largest brains (in proportion to their bodies) and are known to be quite smart! A hummingbird will remember every flower it has ever visited, and how long the plant will take to refill with nectar.

But hummingbirds aren't just beauty and brains - they have some impressive and unique physical traits as well. They boast the highest metabolic rate of all vertebrates, burning energy at about 10 times the rate of a star athlete at his/her peak, and 100 times that of an elephant! With a heart that pulses between 250 and 1,260 times per minute and wings that beat between 70 and 200 times per second, the hummingbird needs copious amounts of oxygen to support its cardiovascular system.

It is for this reason that scientists were surprised to discover over 100 species of the birds living in the Andean Highlands, a mountainous, oxygen-poor region in South America. What was even more astonishing is that some were found as high as 16,000 feet above sea level, an area that has almost no oxygen.

Puzzled as to how the birds are able to thrive in such a rarefied atmosphere, Christopher Witt an ornithologist at the University of New Mexico and Jay Storz, a geneticist at The University of Nebraska-Lincoln, decided to investigate.

They began by collecting blood and tissue samples of 10 species of hummingbirds from colonies that live at varying elevations. What they found was that in order to take maximum advantage of the thin Andean air, the hummingbirds had all adapted by increasing the oxygen trapping abilities of the hemoglobin in their red blood cells.

What was even more surprising was that when the scientists reconstructed the ancestral profile of each species, they found that each breed had colonized separately. This means that they had developed the nearly identical mutation independently and not by interbreeding. As Storz succinctly put it, "Natural selection has hit upon the same solutions time and time again."

The team then set out to compare the DNA of 63 hummingbird species to investigate how these adaptive oxygen-binding traits appeared at the molecular level. That is because very often adaptations that look similar in nature, prove very different at a genetic level. But such was not the case here. It seems that in the high-altitude hummingbirds, the mutation that altered their hemoglobin occurred in the same two amino-acid sites in their DNA sequence.

Though he admits that it makes sense that such a finely honed system might adapt with the same molecular change, Dr. Witt nonetheless calls the discovery, "The most remarkable case of parallel evolution ever discovered." It seems as though the tiny hummingbird never ceases to impress the scientific and bird-loving communities.

Resources:sciencenordic.com,rawstory.com, typesofhummingbirds.com