Body mass-related shift in movement behaviour in the isopod Lekanesphaera hookeri (Isopoda, Flabellifera): A laboratory study

A quantitative study of the movement behaviour of the brackish isopod Lekanesphaera hookeri was performed. Isopods were collected in late spring 2007 from an Italian lagoon and held in the laboratory under temperature-controlled conditions. We used a real-time video acquisition system to measure in resource-free arenas the mean step length, total path length, average movement speed and movement complexity of individuals characterised by a 10-fold difference in body mass. The fractal dimension D was used as a tortuosity index to estimate the complexity of the movement trajectory. No significant size-related patterns were observed for the mean step length, total path length and average movement speed of the sphaeromatids. Conversely, fractal D values varied negatively with the body mass of specimens according to a power law. Our findings indicate that L. hookeri is characterised by a size-related shift in movement behaviour, occurring independently from the availability of resources in the surrounding environment. The implications of size-related changes in movement complexity are discussed in the context of current metabolic theories.