Cuttlefish adjust body pattern intensity with respect to substrate intensity to aid camouflage, but do not camouflage in extremely low light

摘要

Cuttlefish are able to camouflage to a wide variety of natural backgrounds that contain varying colors, intensities and patterns. Numerous studies have investigated the visual cues that influence cuttlefish body pattern expression, yet none have addressed experimentally how well overall intensity is matched between animal and substrate. Here, cuttlefish were tested on artificial and natural substrates that varied in intensity and were illuminated by different light levels; calibrated grayscale photographs were used to analyze the intensity of cuttlefish and their surrounding substrates. We found that cuttlefish scaled their body pattern intensity with respect to substrate intensity under bright and moderate lighting conditions, but not under low or extremely low lighting conditions. Surprisingly, in extremely low light (＜0.0001 lux), cuttlefish did not camouflage to the substrate, but instead retracted most of their dermal chromatophores, assuming a pale appearance. This closed chromatophore body pattern may represent a low-energy choice when cuttlefish have extremely limited visual input. Overall, these results suggest that at light levels most often encountered in the wild, cuttlefish may achieve resemblance to the background by matching the intensity of the substrates on which they are settled, but they do not camouflage in low or extremely low lighting conditions. In addition, our results suggest the possibility that cuttlefish may be able to detect light at an order of magnitude darker than starlight (＜0.0001 lux), as evidenced by the expansion of their chromatophores when exposed to this low light level; however, these cuttlefish did not appear to be able to distinguish patterns since they did not camouflage themselves with respect to the substrate.