Weight as a driver of ontogenetic color pattern shift in the King Ratsnake Elaphe carinata carinata (Günther, 1864) (Reptilia, Serpentes, Colubridae).

In many snakes, the color pattern of neonates differs from that of adults, often superficially resembling a separate species. This phenomenon is known as ontogenetic color pattern shift. Ontogenetic shift may be associated with changes in body weight or age. We addressed this question using the King Ratsnake, Elaphe carinata carinata (Günther, 1864), a species that shows ontogenetic changes in color pattern. Five gravid King Ratsnakes were collected in June 2021 at Huangshan City, Anhui Province, China. Sixty-six fertilized eggs were laid in July, and all eggs hatched and produced neonates in September 2021. Both weight and age since birth were recorded before every feeding, over a period of 22 months. We observed marked ontogenetic color change as snakes grew. As the body weight of the neonates reached ~40 g, the color pattern gradually became a "semi-pattern", where only the color pattern on the front half of the body resembled that of adults. When the body weight reached ~80 g, the "semi-pattern" gradually became a "full-pattern", where the color pattern over the whole body was consistent with that of adults. A subset of individuals did not take food, and thus did not grow at all. These individuals experienced no ontogenetic color change, though they were the same age as ones who did, but were much smaller. Our results show that the color pattern shift in King Ratsnakes is likely associated with body weight, but not age.