9307019 Fleishman Animals communicate with an amazing variety of signals. Even closely related species often have signals that differ greatly in appearance. Understanding how this diversity has evolved has been a major aim of evolutionary biologists since the time of Darwin. Dr. Fleishman will test an important new theory, known as "sensory drive," which suggests that the great variety in the design of visual signals of different species evolved because the different habitats occupied by each species influenced the visual system in a different way. For example, differences in the typical light intensity or background vegetation coloration in a habitat will influence what color and/or motion pattern is easiest to see. Dr. Fleishman will test this theory by studying the evolution of signal diversity in four species of small lizards from Puerto Rico. These lizards, known as anoles, are closely related, but each species occupies a distinctly different type of habitat. Male anoles attract mates and defend territories using visual displays which consist of elaborate motion patterns of the dewlap, a colorful, expandable flap of skin under the throat. Each species has its own dewlap color and its own pattern of motion. In lizards, detection of moving objects by the visual system depends upon a brain structure called the optic tectum. By making neurophysiological recordings from the optic tectum of each species, Dr. Fleishman will determine what combination of stimulus color and movement most effectively stimulates the tectum. He will then make careful measurements, in the field, of the light and color conditions typical of the habitat of each species. He will return to the lab and test the effect of these different light and background conditions on the ability of the optic tectum to respond to moving objects of different colors and motion patterns. He will test the "sensory drive" hypothesis by comparing the color and motion patterns in the actual displays to t he ideal color and motion patterns predicted from the laboratory studies.
