Multi-modal warning signals and target-specific secondary defences in a colour polymorphic, aposematic moth (#505)
Many animals face a life in a multi-enemy world. In order to survive, they have evolved different defensive strategies that vary in nature and efficacy. Aposematic organisms display warning signals that are coupled with some form of unprofitability, for example chemical defences; they are therefore thought to have multi-modal displays. Wood tiger moths (Parasemia plantaginis) are aposematic and, against theoretical predictions, display either white or yellow colouration in their hindwings throughout most of their distribution range; one possible explanation for their co-existence is that yellow males have a more efficient warning signal (the colour itself) whereas white males have a more efficient secondary defence. Chemical defences in wood tiger moths are of two types: secretions from their thoracic glands and abdominal fluids; one likely explanation for the existence of these two types of defences is that they are targeted to different enemies. We collected defensive fluids from lab-reared males of both morphs and tested the response of two biologically relevant predators, blue tits and ants, to their chemical defences. We found that the defensive fluids of yellow males are more of a deterrent to both ants and birds. For both morphs, though, the chemical defences seem to be target-specific: thoracic fluids are especially deterrent for birds, whereas abdominal fluids work against ants. In a second set of experiments, we tested the reaction of avian predators to different combinations of the two colour morphs and the defensive fluids, in an attempt to disentangle the function of wood tiger moths’ multi-modal warning displays. We found that the multi-modal combination of primary and secondary defences seems to be more effective for predator learning than each defence on its own. Our results show that through different chemical defences wood tiger moths get protection from different enemies, but that factors other than predation might be responsible for the maintenance of their hind wing colour polymorphism..