Genomic insights into metabolic flux in ruby-throated hummingbirds

Hummingbirds employ hovering flight, displaying the highest wingbeat frequencies of any bird and sustaining the highest metabolic rates among all vertebrates. Their tissues are very well adapted to sustain efficient and rapid metabolic shifts. Hummingbirds oxidize ingested nectar sugars directly to fuel when foraging but have to switch to oxidizing stored lipids derived from ingested sugars during the night or long-distance migratory flights. The liver plays a vital role in moderating energy homeostasis and the rapid flux from glycolytic to lipogenic metabolism, demonstrated by a remarkable ability to sustain high rates of metabolism using endogenous lipids. The flight muscle must maintain rates as much as 55× greater than the maximum rates observed in any non-flying mammals for transport, uptake and oxidation of circulating sugars. Yet, understanding how this organism moderates energy turnover is hampered by a lack of information regarding how relevant enzymes differ in sequence, expression, and regulation. We generated a chromosome level de novo genome assembly of the ruby-throated hummingbird and used hybrid long and short-read sequencing methodologies for a comprehensive transcriptome assembly and annotation.