Plastic background colour matching in the springbok mantis

Within-species variation in colour phenotypes is widespread in animals. One mechanism by which such variation can be maintained is plastic background matching, where individuals plastically develop a similar colour to that of their surroundings. A few examples are known from insects that exhibit green-brown colour polyphenisms. But the extent to which plastic colour responses are shaped by other factors, such as genetic variation in plasticity or the interaction of other environmental cues, is poorly understood. Here, we investigate the plasticity of body colouration in the springbok mantis, Miomantis caffra—a species where hatchlings emerge brown in colour and typically change to green but sometimes remain entirely or partly brown through successive moults. We reared 350 mantises from 10 full-sib families on a green or brown background under a high or low temperature and a high or low humidity using a fully-factorial, split-brood design, and recorded colour phenotypes (all green, all brown, or mixed colouration) after 14 weeks of development. We found very strong evidence of developmental plasticity for background matching: the green background induced a higher incidence of the all-green phenotype, whereas the brown background produced more of the all-brown and mixed phenotypes. The all-green phenotype was also universally more common under higher humidity, and under higher temperature when the background was green. However, not all body parts showed the same level of environmental sensitivity: the steepest reaction norms were observed in the mid-legs and hindlegs, potentially reflecting the selection for disruptive colouration of the body outline in browner environments. Using model comparison techniques, we found little evidence of genotype-level variation in colour plasticity—a pattern likely the result of strong viability selection for camouflage. Our study shows how developmental plasticity in colouration can be triggered directly by the colour of the environment and indirectly by climatic cues associated with habitat colouration. We argue that this high level of developmental plasticity has likely evolved due to the diversity of habitats but the sedentary lifestyle of this sit-and-wait predator.