Hummingbirds can hover because they lost a gene, study finds

Hummingbirds, native to North and South America, are among the smallest and most agile birds in the world. Often barely larger than a thumb, they are the only bird species capable of flying not only forward, but also backward or sideways. Their characteristic hovering flight makes this possible.

However, hovering is extremely energy intensive. In a genomic study published in the journal ScienceAn international team of scientists led by Professor Michael Hiller from the LOEWE Center for Translational Biodiversity Genomics (LOEWE-TBG) in Frankfurt, Germany, studied the evolutionary adaptations of metabolism that may have allowed hummingbirds to fly in unique ways .

When hovering, hummingbirds beat their wings up to 80 times per second, creating the characteristic buzzing sound. No other form of locomotion in the animal kingdom consumes as much energy. As a result, their metabolism is at full throttle and more active than that of any other vertebrate. To meet their energy needs, hummingbirds rely on the sugar in flower nectar. Hummingbird metabolism also has distinctive features: they quickly absorb sugar, have highly active enzymes that process sugars, and can metabolize fructose as efficiently as glucose, unlike, for example, humans.

Researchers in Frankfurt and Dresden have discovered how birds’ metabolism benefits cells in the flight muscles that allow hummingbirds to glide. In their study, they sequenced the genome of the Long-tailed Hermit (Phaethorn’s eyebrow) and compared this genome and those of other hummingbirds with the genomes of 45 other birds, such as chickens, pigeons and eagles.

They found that the gene encoding the muscle enzyme FBP2 (fructose bisphosphatase 2) was lost in all of the hummingbirds studied. Interestingly, further research showed that this gene had already been lost in the common ancestor of all living hummingbirds, at a time when hovering and nectar feeding were evolving – ago approximately 48 to 30 million years ago.

“Our experiments showed that targeted inactivation of the FBP2 gene in muscle cells improves sugar metabolism. Additionally, the number and activity of energy-producing mitochondria increases in cells lacking FBP2. All of this has already been observed in the flight muscles of hummingbirds,” says first author Dr. Ekaterina Osipova, currently a postdoctoral researcher at Harvard University and previously a scientist at the Max Planck Institute for Molecular Cell Biology and Genetics at Dresden and at LOEWE-TBG in Frankfurt.

“Since the FBP2 gene is only expressed in muscle cells, our results suggest that loss of this gene in the hummingbird ancestor was likely a key step in the evolution of metabolic muscle adaptations required for hovering. “, adds Michael Hiller, professor in the study. of comparative genomics at LOEWE-TBG and the Senckenberg Society for Nature Research.

In addition to the loss of the FBP2 gene, other significant genomic changes likely occurred in hummingbirds. Several other genes that play important roles in sugar metabolism exhibit amino acid changes in hummingbirds, likely due to directed selection. “The relevance of changes in these genes to evolutionary adaptations in hummingbird metabolism needs to be clarified through further studies and experiments,” Hiller said.

Thanks to the Senckenberg Research Institute and the Natural History Museum for this news.

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