Description of Surface Swimming by Hypera eximia LeConte (Coleoptera: Curculionidae): Behavioral, Morphological, and Phylogenetic Implications

Three species of Hypera (H. eximia LeConte, H. postica Gyllenhal, and H. nigrirostris F.) exhibit variable leg morphologies and swimming behaviors. We present morphometric and time lapse video data to document the function of each leg in the swimming behaviors of these weevils. Comparisons weremade betweenH. eximia and two congeneric species that do not have the capacity to swim.Morphometric analyses and extirpation experiments aided in understanding the roles of each individual pair of legs and how each leg segment contributes to the entire legÕs functionality. Hypera eximiaexhibited awell-developed swimming ability,whereasH.postica andH.nigrirostriswereunable to perform any coordinated swimming activity. The capacity for swimming is associated with the different leg morphology of H. eximia. Morphological differences among the three species are signiÞcantly different in prothoracic femoral length, tibial length, tarsal width; mesothoracic femoral length andwidth, tibial length, tarsal width; andmetathoracic femoral width. TheH. eximia swimming behavior is conducted with all three pairs of legs and the rostrum and is manifested in a breast stroke-likemaneuver. Theprothoracic legs areusedprimarily in directionalmovements andbuoyancy compensation, whereas the mesoand metathoracic legs are used asynchronously in forward thrust. Propulsion is accomplished via a 2-phase power stroke with thrust of the mesothoracic leg following the metathoracic leg thrust. Swimming appears to have evolved in three distinct curculionid subfamilies including the Erirrhininae, Ceutorhynchinae, and Hyperinae. We suggest swimming has multiple origins in the Curculionidae and is associated with both behavioral and morphological adaptations.