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.