The effects of light exposure during incubation on embryonic development and hatchling traits in lizards

Abstract

Light is an environmental factor that is known to profoundly affect embryonic development in some oviparous vertebrates, but such effects are unstudied in reptiles. We investigated the light sensitivity of lizard embryos by examining the thickness and light transmittance of eggshells as well as the effect of light on embryonic development and hatchling traits in four lizard species, the Chinese skink (Plestiodon chinensis), the northern grass lizard (Takydromus septentrionalis), the oriental leaf-toed gecko (Hemidactylus bowringii) and the Japanese gecko (Gekko japonicus). The eggshells were thinner and thus had higher light transmittance in Chinese skink than the other three species. Light exposure during incubation significantly accelerated the embryonic development in all species, with higher light intensity resulting in faster embryonic development. Interestingly, light stimulation negatively influenced hatchling size and survival in skinks, but had no effect in lacertids and geckos. This interspecific discrepancy not only relates to the differences in thickness and light transmittance of eggshells, but might also reflect the differences in the reproductive habits of these species. Given the diversity of light conditions that reptile embryos face during development, studies on the response of reptile embryos to light may offer a unique opportunity to understand the mechanisms of embryonic light sensitivity in animals.

Figure 1

The thickness (a) and light transmittance (b) of eggshell in the four lizard species, the Chinese skink (n = 17), the northern grass lizard (n = 17), the oriental leaf-toed gecko (n = 16) and the Japanese gecko (n = 21). The line in the box is the median. Whiskers represent the 10th and 90th percentiles. Black circles beyond the boxplots show the 5th to 95th percentiles. Different alphabets above the boxes indicate significant difference (Tukey’s post-hoc test).

Figure 2

Hatching success (a), incubation period (b) and heart rate (c) of embryos in the Chinese skink, the northern grass lizard, the oriental leaf-toed gecko and the Japanese gecko incubated under dark and light conditions. The line in the box is the median. Whiskers represent the 10th and 90th percentiles. Black circles beyond the boxplots show the 5th to 95th percentiles. Different alphabets above the boxes indicate significant difference (Tukey’s post-hoc test). Sample sizes are shown on the columns or below the boxplots.

Figure 3

Initial egg mass (a) and hatchling morphology (b) snout-vent length; (c) body mass; (d) head length) in the Chinese skink, the northern grass lizard, the oriental leaf-toed gecko and the Japanese gecko incubated under dark and light conditions. The line in the box is the median. Whiskers represent the 10th and 90th percentiles. Black circles beyond the boxplots show the 5th to 95th percentiles. Different alphabets above the boxes indicate significant difference (Tukey’s post-hoc test). Sample sizes are shown below the boxplots.

Figure 4

Hatchling survival rate (a), growth rate of snout-vent length (SVL) (b) and body mass (BM) (c) in the Chinese skink, the northern grass lizard, the oriental leaf-toed gecko and the Japanese gecko incubated under dark and light conditions. The line in the box is the median. Whiskers represent the 10th and 90th percentiles. Black circles beyond the boxplots show the 5th to 95th percentiles. Different alphabets above the boxes indicate significant difference (Bonferroni post-hoc test for survival rate). Sample sizes are shown on the columns or below the boxplots.