Variation in defence and its fitness consequences in aposematic animals : interactions among diet, parasites and predators

Abstract

All animals face a challenge when defending themselves against several different enemies, e.g. predators and parasites. This has resulted in an enormous variation in defence strategies. Individuals have a limited amount of resources to allocate to defence, and thus there can be trade-offs among different strategies. Aposematism is a defence strategy in which an unprofitable animal advertises to predators that it is defended. The most effective warning signals maximize conspicuousness, as this is easier for predators to recognize, learn and remember. The theory of aposematism predicts reduced variation in the warning signal and chemical defence since variation may slow down learning. I have studied causes and consequences of variation in defence strategies against predators and parasites and possible trade-offs among them. My studies with aposematic arctiid moths demonstrate that the size of the signal has a genetic basis, but that it is also affected by diet. Variation in warning signals and chemical defence had surprisingly little effect on predator learning in laboratory experiment with artificial prey items. However, the efficacy of warning colours varied according to changes in the predator community age structure. When there were mainly young, naive predators present, the conspicuousness of a warning signal places the bearer at an increased risk of predation, whereas when most predators are educated about warning signals, the signals protect the bearer. Therefore, the benefit of aposematism as an antipredator strategy varies according to time and place. Genetic and environmental factors, like diet, can constrain the signal expression and defence ability of aposematic animals against predators and parasites partly explaining the large variation in signal design and defence.