First report of rapid eye color change in a non‐avian tetrapod

Abstract

Like coloration of the integument, eye color can be a significant but understudied component of communication and reproductive behavior. Eye color can change with sexual maturation and become sexually dimorphic, but in a few birds and fish, eye color can also change rapidly in response to the environment. There are few cases of the latter, and we report here several instances of such change in eye color in the Eastern box turtle (Terrapene carolina carolina), the first non‐avian tetrapod in which this capability has been reported. In male turtles, the iris changed from a pale yellow color (often characteristic of juveniles) to a bright red color (characteristic of mature males) in a period of <5 s. The nature of the color change is similar to that observed in some birds and suggests a common mechanism and/or adaptive role, which could be further explored in Eastern box turtles.

Estimating the distribution of carotenoid coloration in skin and integumentary structures of birds and extinct dinosaurs

“…We were also aware of instances of tissue flushing, where increased or decreased blood flow to a tissue can alter expressed color; however, because that is a short‐term change to coloration it can confidently be visually distinguished from the use of pigments (see Negro et al., 2006). This also applied to iris tissue, which is highly vascularized and, in some species, has been observed to change rapidly due to flushing (e.g., pigeons [Hollander & Owen, 1939], chickens [Ball 1944], turtles [Carlson et al., 2020]). Again, because this was a short‐term color change it can be visually distinguished from pigmentation.…”