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 in fluencing orientation behaviour, we studied crayfish searching for food sou rces in different artificial streams. Streams differed only in substrate co mposition (sand or cobbles), and the hydrodynamics associated with differen t substrates were quantified. A detailed analysis of orientation paths show ed that crayfish could orient to food sources in streams with either substr ate. The most parsimonious explanation is that animals are using informatio n contained in the spatial and temporal distribution of chemicals in the fl ow to make directional decisions. Crayfish located the source more quickly, spent more time moving, and walked faster while orienting in streams havin g a cobble substrate compared with those having a sand substrate. These dif ferences between substrates were not, seen in control streams. These result s 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 i ncrease orientation efficiency by decreasing search time. On a broader scal e, these results show that it is important to quantify orientation behaviou r in a number of hydrodynamically;different environments. (C) 1999 The Asso ciation for the Study of Animal Behaviour.