A leg model based on anatomical landmarks to study 3D joint kinematics of walking in Drosophila melanogaster
1 Institute of Zoology, University of Cologne, Cologne, Germany
2 Bonn Institute for Organismic Biology (BIOB), Section 2: Animal Biodiversity, University of Bonn, Bonn, Germany
Drosophila melanogaster represents an expedient model organism to study how the nervous system controls terrestrial locomotion, such as walking. Despite recent advances in deep learning-based tracking and kinematic modeling of leg movements of walking fruit flies in 3D, there are still gaps in knowledge about the leg joint biomechanics due to the tiny size of the animals. For example, the natural alignment of joint rotational axes has largely been neglected in previous kinematic studies. Our aim was therefore to create a detailed kinematic leg model in which the main joint rotational axes were based on anatomical landmarks – more specifically, the locations and orientations of joint condyles, obtained from a micro-CT scan of an adult female fly. We found that our model with natural oblique joint axes was able to fit tracked 3D leg postures of walking flies of both sexes with high accuracy. Moreover, we observed that our model showed lower fitting errors compared to an orthogonalized model version, as well as differences in the range of motion (ROM) used. In terms of leg kinematics, we found that the kinematic profiles of front, middle, and hind legs differ in the number of required degrees of freedom of the joints as well as their contributions to stepping, time courses of joint angles, and ROM. In conclusion, our findings not only provide deeper insights into the leg joint kinematics of walking in Drosophila, but will also help in the development of more accurate dynamical, musculoskeletal, and neuromechanical simulations.