Influences of Motivation On Display Divergences in Three Cichlid Fish Species (Haplochromis)

Abstract

AbstractDifferences between three cichlid fish species in responsiveness to a restrained territorial intruder have been investigated while an experimenter, considered a disturbing stimulus, was sitting 2 meters in front of the tank in view of the fish. The purpose of the analyses was to determine which motivational factors control responses to intruders and disturbances between Haplochromis elegans, H. squamipinnis, and H. angustifrons. This could be done on the basis of a model for the causal organization of these responses that was developed in an earlier paper (CARLSTEAD, 1982). It was found that H. angustifrons responds significantly less to the intruder than the other two species, and this is because it responds more to the experimenter. H. squampinnis hides from the experimenter in longer bouts than the other two. It was concluded that angustifrons has a basically higher activation level of system D (refer to model, Fig. 3), a system determining the responsiveness to stimuli indicative of potential danger and controlling motor patterns for hiding responses. Elegans has a relatively higher activation level of system T for responding to territorial intruders. Squamipinnis was found to have a higher level of a general factor for reactivity to all unexpected, thus novel stimuli. Species differences in courtship display were also investigated. These displays differ little between species, but each shows one particular display more often than expected in temporal association with spawning. This display proved in each species to be the display performed more often than expected to a restrained male territorial intruder in the behavior sequence after a conflict to approach it or withdraw from it had occurred (Turning-Around). Using the model, the motivational differences between the three species described above could account for the latter differences. If only one particular motivational configuration can be assumed to be required for a display to occur in any situation, then a approach/withdrawal conflict to a male intruder and a female showing willingness to spawn must elicit the same motivational configuration. It was concluded that species divergences in the activation level of certain motivational factors are reflected in this particular momentary motivational configuration. Characteristics of each species' ecological niche in Lake George, to which they are all endemic, have been discussed with respect to the factors selecting for these motivational divergences, It was concluded that the hypothesis is supported that adaptations for features of a species' habitat may cause divergences in display behavior that are not directly selected for their signal value. This occurs through selection for optimal activation levels of motivational factors that in the behavioral organization control both responsiveness to types of environmental stimuli and motor patterns of display.