Jumping and Grasping: Universal Locking Mechanisms in Insect Legs

Abstract

Thickened femora of insects are correlated to enlarged muscle masses and serve two basic purposes: jumping/kicking and grasping/holding. Modifications on the ventral femoral wall and the tibial flexor tendon that are possibly involved in catch mechanisms have been described in multiple insect taxa with both jumping and grasping legs. Our comparative study aims to explore the functional and structural similarities of these modification in jumping and grasping leg types from Coleoptera, Hymenoptera, Diptera, and Orthoptera with the combination of cutting edge, noninvasive imaging methods, and classical dissections techniques. Our data indicate that locking mechanisms are present in the jumping and grasping legs of insects. We describe three femoro-tibial lock types based on the location of the interacting sclerites relative to the site of origin of the tibial flexor tendon. All of the three types can be found in jumping insect legs, whereas only one type is present in grasping legs. The locking mechanism might aid in keeping the femoro-tibial joint in a flexed position for an extended period of time. Our data indicate that morphologically similar modifications in the femoro-tibial joint are involved in energy-saving mechanisms both in jumping and grasping legs in insects.

A revision of the genus Teleopsis Rondani (Diptera, Diopsidae) in Sri Lanka with descriptions of two new species and a review of the other stalk-eyed flies from the island

“…This leg modification is also referred to as “nutcracker” and can be found in all males, except for small ones. For illustrations of this modification can be referred to Földvári et al (2019 : fig. 4).…”

Parallel and divergent morphological adaptations underlying the evolution of jumping ability in ants

“…In G. destructor, the ratio is 1.08, so that G. destructor has almost equivalent volume of the tibial extensor and flexor muscle, which is a characteristic of walking legs in other insects (Földvári et al, 2019). In Gigantiops, Myrmecia, and Odontomachus the ratio of the tibial extensor to flexor muscle is in fact larger than that of their non-jumping counterparts.…”

“…The ratio of the tibial extensor muscle to tibial flexor muscle is less than unity in most ants, which is a characteristic of grasping legs in other insect lineages (Földvári et al, 2019).…”

“…We looked for evidence for any of the three locking elements identified by Földvári et al (2019) in the micro-CT scans of the femoro-tibial joints in all jumping species; none were found in any of the jumping ants (Suppl. Fig.…”

“…Locusts use hind femur muscles to load strain energy into the semi- lunar process (Bennet Clark, 1975). Another energy storage site is a locking mechanism found in the femoro-tibial joint (Földvári et al, 2019). So far, it is unknown whether the evolution of forward jumping in ants involves elastic energy storage mechanisms.…”