In fact, in order to adapt to daytime light, we and lizards have the same visual structure, that is, cones are scattered all over the retina. This is a type of cell that is built for strong light and is commonly found in the eyes of diurnal vertebrates, such as most birds, monkeys, turtles, and some lizards. But the ancestors of geckos turned to night life because they were too competitive during the day, so the cone cells in their eyes evolved into rod cells that are more suitable for night life, and their functions are very similar to "normal" rod cells. So it is almost certain that geckos evolved from diurnal lizards, but after becoming "geckos", they all became nocturnal animals.

111

If you want to return to daytime, what changes need to be made?


Over time, a group of geckos in Africa found a suitable ecological niche during the day. In order to adapt to the day, their night vision eyes underwent a second transformation, and the processed rod cells turned back into their original cone cells. . But during the previous "night walk", the filtering oil droplets in their eyes disappeared. Now, instead, a special vitamin A derivative in the membrane of the eye sheath allows them to regain the ability to see ultraviolet light.


The theory seems to be established, but is there a transitional species from "nocturnal to day-walking"? It’s true: the most primitive representative of this genus, the Round Island sun-gecko (P. guentheri), can prove this evolutionary law. Characterized by its brownish-grey color and narrow pupils, this gecko is the only species in the genus to retain its original nocturnal lifestyle.

222

Of course, other day geckos are much more colorful than this. Over the course of evolution, most members of this genus have green, yellow, blue, and red patterns on the upper sides of their bodies. While it looks conspicuous on its own, in the wild this makes for surprisingly good camouflage. Even in captivity, it can be difficult to spot a colorful gecko in a terrestrial box surrounded by plants.


Apparently, this special coloration helps the reptile remain undetected by potential predators in its natural habitat. But under ultraviolet light, they can distinguish small differences between the same kind and the environment. In addition, these color differences, especially between closely related species, help identify different species and maintain reproductive isolation. In addition, they can run out and be active during the day, close to human schedules, and are easily observed. These characteristics make diurnal geckos one of the most popular geckos.

333

If you want to adapt to daytime activities, there is another aspect of transformation, and that is the use of ultraviolet rays. For diurnal geckos, there are two important ultraviolet bands, namely UVA (320-400nm) and UVB (260-320nm). UVA in natural light not only allows them to see more colors and distinguish mature flowers and fruits, but also limits excessive synthesis of vitamin D, playing a protective role.


The UVB in natural light can convert previtamin D3 in their skin into vitamin D3, which in turn can absorb calcium. Therefore, UVA and UVB with continuous spectrum are particularly important for diurnal geckos.


So, how do they store absorbed calcium? Behind the eardrum of the diurnal gecko is the cerebral lymphatic organ, also known as the calcareous sac. It consists of a pouch-like endolymphatic sac and a duct, the endolymphatic duct. Both structures are filled with calcium. In addition to their function as balancing organs, they are also practical calcium stores that the female calls upon to form hard eggshells.

444

Therefore, these two types of UV rays are very important for them, whether in the wild or in captivity. Although the spectrum of artificial lamps is not as continuous and perfect as that of the sun, reliable lamps can still largely meet their needs. Most common diurnal geckos are classified into Ferguson zone 3, with UVI values 1.0–2.6 (sunspot zone: 2.9–7.4). But they are not the same as diurnal iguanas. Diurnal geckos adopt a "bimodal" diurnal pattern that is active in the morning and evening, and they avoid the hot periods of noon/afternoon. Instead of emerging after the earth is fully heated like iguanas. Therefore, the environment of diurnal geckos requires more shelter and shelter to effectively prevent them from overheating.

555