WHAT IS THE AIM?
The purpose of the study is to better understand how insects, with their relatively simple nervous system, coordinate their many legs. This is biologically important because insects are one of the largest animal groups. Also, because the fly’s system represents a simple model for neurological processes, this work can yield a better understanding of elementary processes, thereby advancing both neurobiology and robotics as a whole. Our study focused on the tiny sensory organs of the fruit fly Drosophila which are located near its leg joints, known as the campaniform sensilla.
WHAT METHODS WERE EMPLOYED?
The study involved three methods employed in combination: High-speed cameras were used to record the three-dimensional movement of the flies’ legs. Our partners in the USA employed motion methods known as “inverse kinematics” and “inverse dynamics” to calculate the relevant force of footfall. As the final piece of the puzzle, electron microscopy was employed to trace the precise internal and external geometry of the sensory organs on a scale of thousandths of a millimeter. The data obtained through these three methods were integrated in order to build and then run a a computer simulation of how the sensory organs undergo deformation when the creatures scurry around on their legs. As a last step we compared the stress levels against the stress known from the literature to be necessary to mechanically activate sensory cells by ion influx.
WHAT WERE THE KEY FINDINGS?
Employing the model we were able to show that the stress load during normal forward walking does not suffice to activate these small sensory organs located on the creature’s thighs. Our findings support alternative explanation models of how the sensory organ is activated and functions at this position, such as by local muscle forces. While flies are not as strong as ants, for their size they are still powerful. Insects have many mechanical sensory organs, not all of which need to provide input for each individual behavioral action, thus what we have observed here represents a piece of a fascinating puzzle—and the more we discover the more questions arise. The model has been made available as open source, which facilitates its use in studies involving other animals and research questions.
WHAT COMES NEXT?
Since forward walking apparently does not suffice to activate this part of flies’ mechanical perception system, we intend to look at other behaviors or movement situations, such as walking upside down on the ceiling, that could do so. We will also be looking at other model systems, and have plans to study other sensory organ positions as well—for insects have sensory organs like these nearly everywhere on their legs and body.