Polychromatic Midas Cichlids Respond To Dummy Opponents: Color, Contrast and Context

Abstract

Dummies allow the analysis of the effects of striking visual traits free of the confounding variation and interaction seen in live stimuli. In the Midas cichlid ('Cichlasoma' citrinellum), gold morphs (G) dominate normal (N) ones, apparently because an all-gold fish is a 'supernormal releaser' of fear. Although in other fish a dummy that looks like a territory holder or a dominant individual usually evokes the most aggressive response, we wondered whether the gold color was special and would depress aggressiveness. If so, when shown four differently colored passive dummies, gold ones would be approached and attacked least. The other three colors, all naturally occurring, were gray, white and black. Based on earlier, indirect evidence, we predicted that the N and G subjects would not differ in their responses, nor would males and females. We found that gold dummies were attacked at the highest rate, not the lowest, but all dummies were approached about equally. G and N subjects did not differ, nor did males and females based on attack rates. Females, however, spent more time close to the dummies than did males, possibly prospecting for a mate. To 'calibrate' the responses, we then presented to male subjects dummies colored gold, gray, and two novel colors, green and blue. The dummies were attacked from most to least in that order. The novel colors produced greater differences in responses than did colors normally found in the Midas cichlid. Other tests using dummies altered the position of the gold patch that is normally found on the throat, eye color, eye position, proportion of body colored gold, and species-typical markings; a patch of gold covering just the face was particularly evocative. The response to G may depend on whether the encounter is symmetrical or asymmetrical. Gold and gray dummies that threatened back were alternated with passive ones of the same color. Reactive gold and gray dummies were attacked at the highest rates and about equally; they were approached less than were the passive dummies, however. The results of testing with dummies can produce contrary results depending on whether the dummy is reactive or passive, and on the color of the background.