Inactive Tropical Bush Frog Detects Light Through Skin to Adjust Body Colour Intensity for Camouflage

The data were collected as part of an investigation to determine the reason for the tropical bush frog Raorchestes jayarami's colour change. In the dry season of early 2021, in the Idukki region of the southern Western Ghats, India (9°54'53.5"N, 77°13'44.2"E; 800 m MSL; fragmented evergreen and semi-evergreen forests interspersed with cardamom plantations on undulating terrain), we encountered a group of three Raorchestes jayarami, inactive (presumably sleeping) on a shrub leaf, concealed from plain view, approximately one metre above the ground. We observed the day and night activity of the group for 54 days continuously, but the current investigation focused on one individual, identifiable from a dorsal body scar (Adult; SVL=27mm; unknown sex). The study was conducted entirely in a natural environment, without waking the frog from inactivity to avoid stress or consciousness affecting colour change and homeostasis. On 12 February 2021, fourteen observations were made from 6:40 AM to 6:54 PM at one-hour intervals. A single observation included three photographs (Nikon Coolpix B700: Auto mode, Fixed white balance - 4150 K, NEF format with EXIFs preserved): The first photograph was taken immediately after uncovering to capture the frog's original colour, the second photograph captured the visible colour transition in natural light, and the third after the colour change visibly stopped and stabilized. The three photographs accounted for the time taken for partial and complete colour transitions, while the third photograph was used for further analysis since it represented the most stable colour of the frog at that light intensity. The frog was left covered in ambient conditions for one hour before recording another observation. With instruments fixed within one meter of the frog, body and substrate temperatures (From the centre of the dorsal body and 10mm away from the frog: FLIR TG54 Infra-red Thermometer), ambient temperature, and humidity (Kestrel 3500 weather station) were recorded for each observation. Over-/underexposed photographs or those with excess reflections were not considered for analysis. To see how colour changes could be affected by the incident light, we analysed the photographs for colour change (Delta E), change in exposure value over time (Delta EV), achromatic contrast, and colour components (chroma, hue, brightness) in CIELAB colour space (Standard 2007). The frog’s body was divided into 100 segments vertically to test if each segment behaved independently to incident light in the first fourteen observations. To investigate the role of camouflage, the achromatic contrast between the frog and the substrate was measured. References STANDARD, C. J. I. S. 2007. Colorimetry-part 4: CIE 1976 L* a* b* colour space. 2019-2006.