Structure and social significance of vocalization by Anolis grahami grahami (Sauria: Iguanidae)

Abstract

Even though the ability to produce vocalizations by the vibration of a membrane is widespread throughout the lizard suborder, only the sounds of geckos (Gekkonidae) have been closely studied. The purposes of this study were to describe the physical structure, social significance, and means of sound production by Anolis g. grahami, one of the 13 anoline species known to vocalize. Recordings were made of 16 adult males and five adult females within two general situations: (1) while held in an experimenter's hand, and (2) while unrestrained within a cage. Hand-held lizards produced five types of vocalizations: (1) two kinds of growls, (2) two kinds of squeals, and (3) a chirp. Unrestrained lizards vocalized during fights only, producing one type of sound in attacks and another during prolonged fights. Lizards responded only slightly to recorded vocalizations and little more to environmental sounds. This suggests that they do not respond to sounds generally and that vocalizations therefore have little intraspecific use. The most important use of vocalizations is probably in defense against predators, and it is a preadaptation for social communication. Vocalization is scattered throughout the genus and therefore seems to be produced by a structure present in most species which is more highly elaborated in vocal species. Dissections revealed that vocal cords are absent, but that the larynx is nevertheless the site of sound production. A thin membrane within the glottis is proposed as the vibrating structure.