INSIGHTS IN ECOLOGY, BEHAVIOR, AND REPRODUCTION FROM VISUAL MODELS OF AFRICAN CICHLIDS

Abstract

Sexual selection has long been proposed to have played an important role in the explosive speciation of east African cichlids. Further, it is known that visual signals are the most salient ones to cichlids when it comes to reproduction. However, studies examining visual signals such as egg spots and size have been historically difficult to conduct due to the relationship between such phenotypes and confounding variables like age. In addition, the results from such studies often conflict and do not highlight clear patterns and hypotheses. In this dissertation, I use a receptor noise limited (RNL) visual model of increasing complexity to examine the discriminability of important visual signals in cichlid ecology, behavior, and evolution. In determining whether cichlid egg spots are truly mimics of cichlids eggs, I quantified fish and egg reflectance and found that two cichlid species are unable to distinguish the colors of eggs and egg spots in the lighting of their natural habitat. In order to bring together these quantitative methodologies with behavioral data, I tested the viability of using virtual stimuli displayed on a monitor to robustly examine how various visual signals affect conspecific male aggression. I found that although the cichlid Metriaclima zebra responds to virtual stimuli with equal aggression as towards live fish, it also responds with equal aggression towards virtual stimuli that differ in egg spot presence, body color, movement, and size. This suggests that virtual stimuli are not useful for behavioral tests in this species. Finally, in order to examine the salience of egg spots and body color in the wild, I calculated chromatic distance as a function of viewing distance for cichlid body colors against biologically-relevant backgrounds, conspecific body colors, and heterospecific body colors. The study shows that M. zebra body colors are discriminable from the space light at up to 5 m, but from the rocks at shorter distance, though distances that are comparable to the spacing of male territories. This suggests that males should be able to discriminate potential conspecific rivals on their breeding territories. Additionally, the visual model shows that M. zebra is highly discriminable from yellow heterospecifics but not so from blue heterospecifics. This dissertation emphasizes the importance of avoiding human biases in studies of cichlid color vision and behavior.