Owls are one of the rare avian predators that catch their prey by night, and new research suggests that there's something special in the way the DNA molecules in their eyes are packaged, giving them a powerful visual advantage in the dark.
Through the process of natural selection, the new study proposes that the DNA in the retinal cells of owls may have been put together in such a way that it acts as a sort of lens or vision enhancer, improving eyesight during the night.
The unusual trait hasn't been seen in birds before, which hints that owls have gone it alone on this particular evolutionary path, at least among birds. The majority of birds are diurnal, like we are – being most active in the day and sleeping it all off at night.
"In the ancestral branch of the owls, we found traces of positive selection in the evolution of genes functionally related to visual perception, especially to phototransduction, and to chromosome packaging," write the researchers in their paper.
The team looked at the genomes of 20 different bird species, including 11 owls, identifying where positive selection had occurred – where beneficial mutations had been kept over generations. As expected, a lot of this has happened in the areas of sensory perception, which is why owls can hear and see so well.
But the team also discovered signs of accelerated evolution in 32 genes that were more of a surprise. These genes were linked to DNA packaging and chromosome condensation – as if the structure of the molecules inside the owl eyes had actually adapted themselves to be able to capture more light.
A similar change in DNA molecule arrangement in retina cells has been seen before in nocturnal primates, and computer models of their molecular structure have suggested they can channel light.
This isn't the only evolutionary boost that owls have for peering through the gloom – they also have retinas packed with rod cells for better night vision, for example – but it would definitely help in catching prey after dark.
Although the researchers' claims remain hypothetical, it's an intriguing idea. The comparison of genomes also supports the idea that owls did indeed evolve from an ancestor that was diurnal - seeing as the largest changes observed in their genetics seem to be related to enhancing night-hunting abilities.
While owls kept the sharp talons they share with day-hunting birds of prey, like eagles and falcons, the researchers found genes that differed from owls' ancestors, and one that might potentially enhance their excellent hearing, night vision, and soft feathers for silent flight. If the study's findings are confirmed, even the DNA molecules seem to be boosting the excellent sight capabilities of owls.
The authors caution their proposed roles for the differing genes are only suggestions for the moment, particularly with regard to how photoreceptors in owl eyes actually function. Direct observations and analysis may be able to build on the findings outlined here, and could tell us even more about how owls gained their evolutionary advantages.
"Our study suggests novel candidate genes whose role in the evolution of owls can be further explored," write the researchers.
The research has been published in Genome Biology and Evolution.
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October 26, 2020 at 09:04AM
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