The authors in this paper look at how ambient light in the environment might drive the evolution of coloration and reflectance in a beetle species that is active during dusk. The species of scarab beetle, Coprophanaeus lancifer, was examined for brightness of contrast between the horn and pronotum at close distance and the body and the forest floor where they live to determine the support of a sensory-drive hypothesis as the evolutionary drive behind the beetles’ coloration.

The beetles are a dark violet-blue and are most active during dusk, when there is low ambient light, and they live in a dense forest environment with gaps and shade patterns. Previous studies have mostly compared colorations or contrasts based on ambient light in different light environments in a forest, but not taken the time of day into account. They note studies involving birds and other insects both for long distance brightness contrast and color contrasts at short distances.

For the beetle used in the experiment the pronotum is the brightest part of the body, and the horn is the darkest, so if another beetle looks head on they see the dark horn against the brighter, shinier body. There is no sexual difference in color contrast in any of the different light environments. Reflectance was taken at different distances, since the body contrasting with the ground cover is usually seen at far distances, but the horn contrasting with the rest of the body is seen at close distances by other conspecifics. It is surmised that habitat choice may drive the evolution of the body coloration patterns to optimize their detection by conspecifics and for signal detection.

This topic of reflectance and body coloration was discussed in the lecture on light signals. The animals emitting the signals try to maximize the transmission of the signal depending upon the environment and different light conditions. We also discussed the use of contrast by different animal species as a way to increase the signal detection by the receiver. Contrast in lecture was referred to not only as contrast between color patterns on an animal, but also between the animal and the background upon which it is emitting the signal. According to a chart in the lecture regarding the optimal signals and background hues the optimal signal color for broadleaf litter is blue, so the C. lancifer beetle with its dark violet-blue coloration fits in with what one might expect to see for an animal trying to make a visible signal.