Evolutionary insights into Felidae iris color through ancestral state reconstruction

There have been very few studies with an evolutionary perspective on eye
(iris) color, outside of humans and domesticated animals. Extant members
of the family Felidae have a great interspecific and intraspecific
diversity of eye colors, in stark contrast to their closest relatives, all
of which have only brown eyes. This makes the felids a great model to
investigate the evolution of eye color in natural populations. Through
machine learning image analysis of publicly available photographs of all
felid species, as well as a number of subspecies, five felid eye colors
were identified: brown, green, yellow, gray, and blue. Using phylogenetic
comparative methods, the presence or absence of these colors was
reconstructed on a phylogeny. Additionally, through a new color analysis
method, the specific shades of the ancestors’ eyes were quantitatively
reconstructed. The ancestral felid population was predicted to have
brown-eyed individuals, as well as a novel evolution of gray-eyed
individuals, the latter being a key innovation that allowed the rapid
diversification of eye color seen in modern felids, including numerous
gains and losses of different eye colors. It was also found that the gain
of yellow eyes is highly associated with, and may be necessary for, the
evolution of round pupils in felids, which may influence the shades
present in the eyes in turn. Along with these important insights, the
methods presented in this work are widely applicable and will facilitate
future research into phylogenetic reconstruction of color beyond irises.