Turning lances into shields: Flower mantids stretch their raptorial forelegs to avert and deflect predator attack

Evolutionary co-option, in which existing traits acquire novel adaptive
functions, is a key strategy by which organisms adapt to new environmental
challenges. Although such co-option has been widely documented at the
genetic and morphological levels, its incidence at the behavioural level
remains largely unknown. Mantids stretch their forelegs to capture prey;
however, some flower mantids also perform foreleg stretches in the absence
of prey. The current study tested whether this behaviour represents a
novel function of the foreleg stretch, thus representing a case of
behavioural co-option. Predator encounter behaviour assays revealed that
foreleg stretching facilitates the escape of flower mantids from large
predatory mantids by delaying predator approach or deflecting their attack
towards less vulnerable body parts. Phylogenetic analysis suggested that
the ancestral function of foreleg stretching involves prey capture, with
the anti-predator function subsequently acquired in the flower mantid
clade, coinciding with the diversification of large-sized mantids, the
most likely invertebrate predators of flower mantids. This study provides
a case of behavioural co-option, where a predator uses its predatory organ
as a defensive implement to cope with its own predators. These findings
further suggest that behavioural co-option may be common in nature,
meriting more comprehensive studies.