Owls are expertly trained nighttime assassins, tracking down prey in the lowest of light conditions, and new research may have pinpointed the genetic mutations that gave them this superpower. Published in the journal Genome Biology and Evolution, the research has identified a unique way that DNA is packed into the molecules in their eyes that basically gives them night vision.
Most bird species are diurnal, meaning they are most active in the day and rest at night, like humans. To find out how owls had managed to monopolize on nighttime hunting, they looked at the genomes of 20 different bird species, including 11 owls, to see where beneficial nighttime traits had been selected for over generations.
By focusing on which mutations had been kept over generations, indicating they were beneficial, the team recognized that this was happening most in areas that coded for sensory perception, such as eyesight and hearing. No surprises there. The same process of natural selection explains why owls have such good hearing, with two holes surrounded by filamentous ‘auricular’ feathers that bounce sound into the ears. Their ears are also asymmetrical, with one sitting higher on the head than the other, which combined with the aerial dish-like faces make it easier for the bird to pinpoint where a sound is coming from.
What was surprising was that there was evidence of accelerated evolution in 32 genes linked to chromosome condensation and DNA packaging. This kind of DNA rearranging has been identified before in the eyes of nocturnal primates, indicating the molecules within the eye can change over time to capture more light.
Computer modeling along this theme appears to confirm that this restructuring could indeed improve night vision through this mechanism, with the DNA in the retinal cells acting like a night vision lens to boost sight in the night. While it’s too early to draw firm conclusions regarding the role of these mutations on night vision in owls, the mutations present an interesting route to night vision as it would imply the owls' relatives were diurnal species whose genetic code had to be reworked to give rise to our nighttime assassins’ nocturnal skill set.
“Our results support that owls — similar to other nocturnal birds — early on evolved sensory adaptations that allowed them to cope with dim light,” wrote the study authors. “In particular, phototransduction in the rods, enhanced motion detection and retina repair, but also acoustic perception seem to be important for the owls. We also found evidence for functional overrepresentation associated with chromosome packaging. This suggests a role of chromatin packaging for enhanced light channeling in photoreceptor cells as a target of adaptation in the owl ancestor.
"Our study suggests novel candidate genes whose role in the evolution of owls can be further explored.”
