Birds that feed on sugar-rich nectar and fruit show remarkably similar genetic adaptations, despite their diverse evolutionary backgrounds. These include representatives of hummingbirds, honeyeaters, sunbirds, and certain parrots. Researchers report this in Science of 26 February. Across multiple independently evolved lineages, the same genes and regulatory DNA regions appear to have been modified to support high sugar intake, without the metabolic disruption that so often occurs in mammals.
The researchers assembled reference genomes for five nectar- and fruit-eating species and compared these with four related species that do not follow a sugar-rich diet. Using comparative genomic analyses, they searched for convergent evolution: independent changes in the same genes. In doing so, they found repeated adaptations in genes involved in sugar metabolism and insulin signalling. In all the sugar-eating lineages studied, changes occurred in the gene MLCIPL, which encodes a transcription factor that regulates glucose metabolism and fat production.
Birds naturally maintain higher blood glucose levels than mammals and are less dependent on insulin. According to the authors, changes in MLCIPL likely enable excess glucose to be efficiently converted into fat reserves, which are then drawn upon during fasting.