Behaviors guided by vision

Visual cues, usually in the form of prey movement, have long been known to attract a snake's attention and to elicit predatory responses in insectivorous lizards. Equally interesting is the role of visual information in social and reproductive behavior of lizards. Chameleons exhibit "emotional colors" that involve changes in brightness during agonistic interactions and culminate in victory or submission, each with a characteristic pattern. It is partly through these color changes that chameleons have acquired their protean reputation. Iguanian lizards execute a set of movements, including head bobs, pushups, and dewlap extensions, combined in particular sequences that are species specific not only with respect to sequence but also with respect to cadence. Females of sympatric species can discriminate conspecific from het-erospecific males on the basis of these display properties. Males use the displays to advertise territories and to settle boundary disputes with other males.

Results of experiments involving presentation of models to territorial males have established that color patterns and postures contribute to agonistic and courtship activities. These behaviors have been found to be innate, and the development of the behaviors is not influenced by social stimulation. Some display elements of the green anole (Anolis carolinensis) are present immediately after hatching, whereas other elements emerge later in ontogeny. Even in the later stages, social stimulation appears unnecessary, because the behaviors usually emerge on schedule in animals that live in social settings or in experimental isolation. This characteristic represents a major difference between green anoles and birds and mammals, both of which typically depend on early social stimulation for the proper development of social signals. Because only the green anole has been studied extensively in this regard, we look forward to comparable projects with additional reptile species. Only when such work is completed will we know whether the developmental characteristics of the green anole are common among reptiles. The indications are that the green anole is a reasonable model for reptiles in general, and many herpetologists believe this to be the case, but more taxa must be analyzed.

Reptiles use visual cues as lures for prey. The alligator snapping turtle (Macrochelys temminckii) is probably the best known example because of the wriggling wormlike process attached to the floor of the turtle's mouth. The animal remains motionless with jaws agape while the "worm" attracts fish, which are engulfed by a profound oral snap. Several snakes (e.g., the sidewinder rattlesnake [Crotalus cerastes] and the mas-sasauga [Sistrurus catenatus]) use their tails as lures, in some cases only during the juvenile stage of life. As the snakes grow, they experience an ontogenetic shift in prey preferences such that caudal luring for lizard or frog prey is abandoned in favor of predation on rodents. Ontogenetic shifts in prey preferences are not uncommon, and they are associated with parallel ontogenetic shifts in habitat preferences and even in diel activity patterns. Some snakes rely on caudal luring throughout life. The best example is the death adder (Acan-thophis antarcticus), which has a highly specialized tail that strongly resembles a wormlike or grublike creature and is quite attractive to lizards.

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