Effect of warning colours in prey varies according to season
Seasonal differences in the survival of caterpillars, conspicuous versus camouflaged, depend on the learning and experience of young birds, reports a study published in Nature Communications this week. This time lag in predator learning could explain why conspicuous prey are rare at certain times of the year. The study was conducted by a research team at the University of Jyväskylä headed by Professor Johanna Mappes from the Academy of Finland’s Centre of Excellence in Biological Interactions Research.
To avoid being eaten, caterpillars of different butterfly species have evolved to either blend into their backgrounds or advertise themselves as harmful to would-be predators using conspicuous ‘warning’ signals. However, conspicuous advertising is a risky strategy as it relies on predators understanding what these signals mean.
Johanna Mappes and colleagues investigated whether the abundance of differently coloured caterpillar species might be influenced by the number of juvenile bird predators, which are naive to the meaning of warning signals from conspicuously coloured prey, when they first leave the nest.
The authors find that conspicuously coloured caterpillars have improved survival at the beginning and end of the fledging season, when naive birds are least abundant, while camouflaged species have a survival advantage during the middle season. These same seasonal abundance patterns are reflected in nature across many caterpillar species of differing colours, and could explain why warning signals persist when predators have no innate knowledge of their meaning.
Mappes J, Kokko H, Ojala K & Lindström L. Seasonal changes in predator community switch the direction of selection for anti-predatory defences. Nature Communications doi 10.1038/ncomms6016