Benjamin Puttler

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

Abstract 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 were made between H. 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 leg’s functionality. Hypera eximia exhibited a well-developed swimming ability, whereas H. postica and H. nigrirostris were unable 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 significantly different in prothoracic femoral length, tibial length, tarsal width; mesothoracic femoral length and width, tibial length, tarsal width; and metathoracic femoral width. The H. eximia swimming behavior is conducted with all three pairs of legs and the rostrum and is manifested in a breast stroke-like maneuver. The prothoracic legs are used primarily in directional movements and buoyancy compensation, whereas the meso- and 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.