A Comparative Study of Display Behavior in Phrynosoma (Iguanidae)

Abstract

The behavior of six of the seven species of Phrynosoma found in the United States was studied. Most of the behavior patterns typical of iguanids are lacking in this genus. Analysis of display-action-pattern graphs is presented. These show a gradual decrease in display complexity from primitive to more recent forms. A hypothesis is presented to account for the loss of the display. It has long been known that members of the family Iguanidae perform bobbing motions of the head. In his studies on the behavior of this family of lizards Carpenter (1961a, 1961b, 1962a, 1962b) has found that these motions constitute a ritualized species-specific display pattern used for asserting dominance, defending the territory, sex recognition, and to some extent courtship. Hunsacker (1960) has indicated a possible use in species recognition. Carpenter (1961a) has further pointed out that specific differences in ritualistic behavior patterns, such as the display in iguanids, may be, along with morphological and physiological characteristics, the result of environmental selection. Investigations now underway show some indication of correlation between the elaborateness of the display and the site in the habitat where the lizard is usually active. It might also be expected that closely related forms which show a progression in morphological and/or physiological characteristics would also show a similar progression in behavioral characteristics. This study of the United States forms of Phrynosoma was undertaken with these ideas in mind. MATERIALS AND METHODS. Seven species of homed lizard occur in the United States. I have been able to study six of these: P. platyrhinos, P. modestum, P. coronatum, P. solare, P. cornutum, and P. douglassii. The homed lizards used in this study were obtained in the southwestern United States by personal collection, by gift from friends and resident herpetologists, and by purchase. The lizards were kept and studied in cages and in large outdoor enclosures where an effort was made to simulate the natural habitat. The lizards were fed meal worms, the contents of sweep nettings, and large red agricultural ants. Water was available at all times. A system of toe clips was used for permanent marking of individuals. Model airplane dope in various