Temperature-Dependent Warning Colour Variation in an Aposematic Insect

Aposematic colouration in animals advertises prey toxicity and unpalatability to predators. However, intra-specific variation in aposematic signals is widespread and often thought to be the result of environmental factors such as temperature. To investigate how temperature affects warning colour, we used the aposematic seed bug Lygaeus simulans as a model. Wild-type adults of this species exhibit the typical red and black pattern common among many aposematic insects, while "pale" mutants are yellow and black. Here, we investigated how rearing temperatures affect their warning colour, fitness traits, and protein expression. We found that L. simulans warning colouration is temperature sensitive, with both pale-mutant and wild-type individuals redder at lower temperatures (24°C) compared to higher (32°C) temperatures. Reduced body size (weight and length) was also found at this lower temperature. Utilising SWATH-proteomic analysis, we identified 15 differentially expressed proteins between the two morphs, including Glutathione S-transferase (GST), a protein involved in oxidative states. Subsequent analysis of GST activity showed higher activity in pale-mutants compared to wild-types at 29°C. Furthermore, in males, this difference between morphs mirrored the colour change as it was not evident at 24°C, although this was not the case in females. Our research reveals a distinctive temperature-dependent variation in aposematic colouration, providing a greater understanding of how warning signals evolve with temperature changes.