Locomotor studies in small organisms are usually performed through indirect measurements (reporter genes) or video recording (bug trackers).
The commercialization of the Drosophila melonagaster activity monitoring system (Trikinetics www.trikinetics.com) caused a big impact on research of this animal model. The main characteristic of this equipment is the possibility of recording the activity of a large number of animals, with single animal tracking. This equipment is used in chronobiology and in pharmacological studies involving research from many areas such as Parkinson disease, aging, and toxicity.
However, behavioral studies in smaller organisms have been limited to population measurements or the indirect recording of reporter gene activity. For example, bioluminiscent reporters have been used in cianobacteria; whole population measurements of oxygen consumption and metabolic production or biomass growth have been used for yeast; impedance and optical density of the medium have been employed for bacteria.
Other model organisms, such as zebrafish larvae or the C. elegans nematode, have been studied through reporter genes (bioluminisense and biofluorescence) and through video tracking (using video recording plus digital image analysis).
At the moment, complex movement analysis is only possible using ‘bug trackers’. However, the implementation of this setup for multiple channel tracking (high number of isolated animals) is not practical. The elevated cost of CCDs and optical equipment, plus the huge amount of data processing required (equivalent to one camera coupled to one microscope, plus one PC per camera) makes it difficult and expensive to use for multi-isolated-organism tracking.
The study of simpler behaviors, such as the possibility to know if an animal moves in one particular moment or even if it is alive, requires simplified systems with the possibility to track multiple individuals simultaneously and real time data processing.
The locomotor system designed for Drosophila and similarly sized insects (Drosophila size=5 mm long×3 mm wide, opaque colour) is not suitable for smaller animals. When we attempted to use this system for smaller organisms (i.e. C. elegans, about 1 mm long×100 um diameter, translucid) we found many limitations. To name a few: inappropriate culture recipient format (glass tubes of 5 mm diameter), big size of the infrared beam relative to the small organism body (beam=3-5 mm diameter vs. organism=100 um) and lower than required detection sensibility (since flies are not transparent).