| Popis: |
The present study analyses the olfactory mediated orientation behaviour of three crayfish species, Astacus leptodactylus, Austropotamobius torrentium and Procambarus clarkii, in a turbulent odour plume under different hydrodynamic conditions. Based on a hypothetical rheotaxis mechanism of chemo-orientation, the time course of simultaneously acquired parameters of the flow field and behavioural parameters were analysed. A cross-correlation between heading (i.e. angular difference between search direction and target direction by means of counter-current direction) vs. turn and flow direction vs. walking direction respectively was established. In case of heading vs. turn this correlation was strongest with a time shift of approx. 800ms. With this time shift heading and turn show strong coincident time courses. The time shift was interpretated as the reaction time of the animals, which is invariable over the total search time. As a result crayfish walked with individual latencies between 2 and 5 seconds against the incident water current. This analysis revealed a strong dependency of walking direction on flow direction. In the absence of olfactory cues crayfish did not show rheotactic orientation. Unilateral inactivation of antennules had no effect on search success or orientation behaviour in detail (i.e. parameter constellation) suggesting that a chemo-tropotactic orientation mechanism involving left vs. right comparison of bilateral receptors was not necessary to describe chemotactic behaviour. Inactivation of both antennules prevented an initiation of odour mediated search. These results suggest that one role of olfactory cues is to induce odour-orientation while the hydrodynamic stimulus controls the direction of orientation reaction of crayfish. In contrast walking speed is a critical behavioural parameter and did not correlate to any hydrodynamic parameter. There are some evidences that this parameter may be controlled by some aspects of the turbulent nature of the chemical stimulus, e.g. odour puls parameter like puls onset-slope. Together these results suggest a bimodal mechanism of chemo-orientation in crayfish and maybe in other decapod crustaceans. |
