LATERALITY IN DETOUR BEHAVIOR - INTERSPECIFIC VARIATION IN POECILIID FISH

We measured whether males of five species of poeciliid fish made detou rs to the right or left of a vertical-bar obstacle in order to approac h a group of females. Three of these species, Gambusia holbrooki, Gamb usia nicaraguensis and Poecilia reticulata showed a significant bias t o the left, whereas Brachyrhaphis roseni and Girardinus falcatus showe d a significant bias to the right. When tested for direction of turnin g in front of an opaque barrier, or when a dummy predator was used as a target in a detour test, G. holbrooki and G. falcatus showed similar biases to the right (opaque barrier) and left (predator), thus sugges ting that the difference observed when females were used as a target c ould arise from species differences in the degree of sexual motivation in a novel environment. The two species that showed bias to the right with the females were less likely to exhibit sexual behaviour when pl aced in a novel environment. Moreover, manipulation of the factors aff ecting the relative strength of sexual motivation and of fear of a nov el environment, such as how long fish were maintained in captivity or in the test apparatus before being tested, caused shifts in the direct ion of the lateral asymmetries. These results suggest that the presenc e of functional asymmetries in behaviour could be widespread among ver tebrates and that the direction of such asymmetries tends to be striki ngly similar in closely related species, thus supporting the hypothesi s of an; early evolution of laterality in brain and behaviour. (C) 199 7 The Association for the Study of Animal Behaviour.