Red light accelerates and melatonin retards metamorphosis of frog tadpoles

Abstract

Background: Earlier studies from this laboratory reported that light and its spectra influence reproduction in the Indian skipper frog Rana cyanophlyctis through both ocular and extra ocular photoreception. During the course of our ongoing studies on chromotactic behaviour of the tadpoles, we noticed that tadpoles held in red light metamorphosed earlier than those held in white or other colours of light. The focus of the present study therefore was to examine the effect of red light on metamorphosis of the tadpoles.

Results: Tadpoles, both intact and blind (optectomised), held in red light metamorphosed earlier than those held in white light. Addition of melatonin to aquarium water (5 micrograms/litre) prevented the red light-induced acceleration of metamorphosis both in intact and blinded tadpoles.

Conclusion: Both ocular and extra-ocular perception of light is involved in red light-induced precocious metamorphosis. Melatonin inhibits the red light-induced acceleration of metamorphosis. The mechanism by which red light accelerates metamorphosis is not yet known. Melatonin counteracts red-light induced acceleration of metamorphosis in this tadpole.

Figure 1

Fore and hind limb regions of the tadpoles. Fore and hind limb regions of the tadpoles held in white light (upper panel) and red (lower panel). The forelimb and hind limb buds are clearly seen in tadpoles exposed to red light.

Figure 2

Body weights of tadpoles in different experimental groups. Panel A: Intact tadpoles held in white light, held in white light and treated with melatonin, held in red light only, held in red light and treated with melatonin. Panel B: Blind tadpoles held in white light, blind tadpoles held in white light and treated with melatonin. Panel C: Blind tadpoles held in red light, blind tadpoles held in red light and treated with melatonin. Values are Mean ± SE; **P < 0.01 control vs. treated groups

Figure 3

Tail lengths of tadpoles in different experimental groups. Panel A: Intact tadpoles held in white light, held in white light and treated with melatonin, held in red light only, held in red light and treated with melatonin. Panel B: Blind tadpoles held in white light, blind tadpoles held in white light and treated with melatonin. Panel C: Blind tadpoles held in red light, blind tadpoles held in red light and treated with melatonin. Values are Mean ± SE; **P < 0.01 control vs. treated groups