Chemical orientation to food by the crayfish Orconectes rusticus: influence of hydrodynamics.

Many different organisms orient to chemicals in a variety of habitats. Each of these habitats has a unique hydrodynamic environment that is dependent upon the structure of that habitat. Differences in the hydrodynamics (i.e. turbulence) of an environment will be reflected in the fine-scale structure of chemical signals. To determine what role dispersion dynamics play in influencing orientation behaviour, we studied crayfish searching for food sources in different artificial streams. Streams differed only in substrate composition (sand or cobbles), and the hydrodynamics associated with different substrates were quantified. A detailed analysis of orientation paths showed that crayfish could orient to food sources in streams with either substrate. The most parsimonious explanation is that animals are using information contained in the spatial and temporal distribution of chemicals in the flow to make directional decisions. Crayfish located the source more quickly, spent more time moving, and walked faster while orienting in streams having a cobble substrate compared with those having a sand substrate. These differences between substrates were not seen in control streams. These results show that the hydrodynamics associated with chemical signal structure can greatly influence the temporal properties of orientation to food sources. For crayfish, differences in the turbulent structure of flow may actually increase orientation efficiency by decreasing search time. On a broader scale, these results show that it is important to quantify orientation behaviour in a number of hydrodynamically different environments. Copyright 1999 The Association for the Study of Animal Behaviour.