STRUCTURAL COMPLEXITY IN A LIZARD COMMUNICATION-SYSTEM - THE SCELOPORUS-GRACIOSUS PUSH-UP DISPLAY

Several measures from information theory are used to describe the stru ctural complexity of the Sceloporus graciosus push-up display signal s ystem and to compare this complexity to that of other animal communica tion systems. Data from focal animal observations of both male and fem ale animals in the field are used to describe the push-up display as a simultaneous combination of three components: display body postures ( e.g., lateral flattening, arched back), the number of legs extended du ring the display (0, 2, or 4), and the number, type, and sequence of h ead-bobs. Various grammatical rules are described that govern the comb ination of these components into push up displays. Body postures are s hown to be discrete signals, whereas the number of legs extended and t he pattern of head-bobs serve as graded signals. The three structural components are related to each other such that more head bobs are comb ined with more legs being extended and a greater likelihood that displ ay body postures are used. Males use more head-bobs, extend more legs, and use display body postures more often than do females; and sexual dimorphism is greater during the mating season than after mating has e nded. Finally, the push up display is ''open'' or ''generative'' such that new forms of the signal system will be encountered with an increa sing number of displays observed. Overall, the push up display system is shown to contain most of the types of complexity observed in the co mmunicative displays of birds and mammals.