Evolutionary analysis of vision genes identifies potential drivers of visual differences between giraffe and okapi

Giraffes may detect red light differently from their closest living relatives. Their open savannah habitat presents a very different visual world from the dim forests occupied by okapis. Comparing the genes used by their eyes offered a way to investigate those differences beyond the giraffe's obvious advantage of height.

Edson Ishengoma, Morris Agaba and Douglas Cavener compared 36 vision-related genes from giraffe and okapi genomes with corresponding sequences in other mammals. They looked for evolutionary changes in proteins involved in focusing light and turning it into nerve signals. One candidate was the pigment sensitive to longer wavelengths, which helps determine how an eye responds to different colours.

The sampled giraffes carried two distinctive changes in that pigment relative to the other ruminants compared. One occurs at a position already known to alter wavelength sensitivity, leading the team to predict a small shift towards longer, redder wavelengths. They did not measure giraffe colour perception, and two sequenced giraffes cannot establish that every giraffe carries these changes. Suggestions involving predator detection or recognition of other giraffes therefore remain explanations to test. The discovery identifies a plausible molecular difference in how giraffes receive light, not proof that they see colours better.