Predator–prey interactions are well established as a driving force in organismal evolution, and predator-related natural selection may bring about major changes in morphology and behaviour in evolutionary lineages. Yet, the mechanisms determining the outcome of these evolutionary interactions are unclear: prey and predators may change in response to each other in a coevolutionary‘arms race’, while major predators may trigger the appearance of changes in design in the prey through episodic ‘escalation’. For beetles, varied strategies exist which function to avoid predation. Chemical defence is prevalent in various lineages and has long been recognized as prone to convergent evolution. However, the role of anti-predator strategies in driving morphological adaptation is less clear. Leaf beetles (Chrysomelidae) offer a good system to study predator-induced morphological adaptation and the particular conditions under which complex defensive traits originate. Chrysomelids display a wide range of avoidance behaviours, including flying, running, dropping, feigning death, mimetic concealing and, largely unique to this group, jumping.

Within Chrysomelidae, flea beetles (Alticinae) are characterized by an extraordinary jumping apparatus in the usually greatly expanded femur of their hind legs that separates them from the related Galerucinae. Here, YANG Xing-Ke research team examine the evolution of this trait using phylogenetic analysis and a time-calibrated tree from mitochondrial (rrnL and cox1) and nuclear (small subunits and large subunits) genes, as well as morphometrics of femora using elliptic Fourier analysis. The phylogeny strongly supports multiple independent origins of the metafemoral spring and therefore rejects the monophyly of Alticinae, as defined by this trait. Geometric outline analysis of femora shows the great plasticity of this structure and its correlation with the type and diversity of the metafemoral springs. The recognition of convergence in jumping apparatus now resolves the long-standing difficulties of Galerucinae–Alticinae classification, and cautions against the value of trait complexity as a measure of taxonomic significance. The lineage also shows accelerated species diversification rates relative to other leaf beetles, which may be promoted by the same ecological factors that also favour the repeated evolution of jumping as an anti-predation mechanism.

This research has been online published in Proceedings of the Royal Society B: Biological Science. (Deyan Ge, Douglas Chesters, Jesús Gómez-Zurita, Lijie Zhang, Xingke Yang, Alfried P. Vogler.2010.Anti-predator defense drives parallel morphological evolution in flea beetles. Proceedings of the Royal Society B: Biological Science. doi: 10.1098/rspb.2010.1500)