The evolution of startle displays: a case study in praying mantises

Anti-predator defences are typically regarded as static signals that conceal prey or advertise their unprofitability. However, startle displays are performed by prey when attacked and can include a spectacular array of movements, colours, and sounds. Here we present the first phylogenetically-controlled comparative analyses of startle displays including behaviour, using praying mantises as a test case. For 58 species, with a dated phylogeny, we estimate the strength of phylogenetic signal in the presence and 'complexity' (number of display components) of displays and their components and test hypotheses on their evolutionary correlates including primary defence and body size. We report strong phylogenetic signal in display presence and complexity, and strong lability in behavioural, but not morphological, components. Body size correlates with display presence and complexity independently of phylogeny, but not in phylogenetically-controlled analyses. Finally, species in species-rich clades are more likely to have a display, and a more complex one, suggesting support for ecological displacement via behavioural traits. To further elucidate the conditions under which startle display evolve, future work should include quantitative descriptions of display components, habitat type, and predator communities. Understanding the evolution of startle displays enriches our overall understanding of predator-prey dynamics and provides scaffolding for the development of new theory.