On the evolution of raptorial legs - an insect example (Hemiptera: Reduviidae: Phymatinae).

Abstract

The presence of chelate and subchelate fore legs in Phymatinae (Hemiptera: Reduviidae), or ambush bugs, provides a unique opportunity to study the evolution of different types of raptorial legs in a closely related group of arthropods. Themonocorini have simple, possibly raptorial legs, Phymatini and Macrocephalini distinct subchelate fore legs, and the charismatic Carcinocorini are the only insects with a chelate fore leg apart from female dryinid Chysidoidea (Hymenoptera). Relationships between the four phymatine tribes are here analyzed in a cladistic framework thus permitting testable hypotheses on the evolution of raptorial legs. The presented analysis of phymatine tribal level relationships is based on a dataset comprising 11 species of Phymatinae and 54 non-phymatine Reduviidae and Heteroptera. The molecular data set consists of ∼3500 MAFFT aligned bases of 16S, 28S D2-D3, and 18S ribosomal genes. Parsimony and maximum likelihood analyses resulted in identical topologies for the ingroup with the relationships Themonocorini + (Phymatini + (Carcinocorini + Macrocephalini)) receiving high support values. Eleven morphological characters, eight of them derived from fore leg morphology, were optimized on the parsimony analysis. These optimizations indicate that the ancestral ambush bug had a simple raptorial leg; that size reduction of the tarsus, enlargement of the femur, curvature of the fore tibia, armature of tibia and femur with rows of tiny tubercles that allow for gripping of a prey insect, and the large process on the ventral surface of the femur arose in the common ancestor of Carcinocorini + Macrocephalini + Phymatini. The chelate leg in Carcinocorini is likely derived from a subchelate precursor similar to the one seen in recent Macrocephalini and may have evolved through elongation of the ventral, proximal portion of the fore femur and modification of the median process to form part of the digitus fixus. © The Willi Hennig Society 2010.