Causes and consequences of colour variation in Tectocoris diophthalmus (Heteroptera: Scutelleridae)

Aposematism, the pairing of conspicuous signals with unpalatability in potential prey, is suggested by theory and empirical evidence to be under frequency-based selection for uniformity and maximal conspicuousness. However, this is often not the case in nature, and variation in warning colouration is not uncommon. Studies have generally looked at this paradox from one of two perspectives: the sender's physiological trade-offs, or the receiver's (predators) visual physiology and psychology. Here we consider both perspectives simultaneously, using the highly variable Hibiscus Harlequin Bug, Tectocoris diophthalmus (Heteroptera: Scutelleridae). This shieldback stinkbug has an orange base colour and highly reflectant blue-green iridescent patches that range in size from absent to entirely covering the dorsal surface. First, I critically examined the role of arthropod taxa in aposematism studies, and highlight the valuable contributions to the field further experimentation can make. Then I examined the sender's colour production mechanisms, to identify sources of variation and potential physiological trade-offs. Next I surveyed intra and inter-population variation, to model and empirically test the influence of environmental factors on patterns of variation. Then I tested sensitivity to chemical defences of multiple ecologically-relevant predators, and assayed two disparate taxa (a passerine bird and praying mantid) for their behavioural responses to colour variation, to determine how they may be selecting for or against maintaining variation. In conclusion, colouration in T. diophthalmus is a complex, phenotypically plastic trait under multiple selective drivers to create and maintain variation. By looking at the perspective of both sender and multiple receivers, we now have a more complete, cohesive, and holistic understanding of intraspecific variation of warning colouration in this species.