Predation reduces visual communication distance in an Anolis lizard

In his book Descent of Man and Selection in Relation to Sex, Darwin (1) made a compelling argument that evolution could not be explained solely on the basis of differential survival (natural selection). In particular, traits that enhance an individual’s reproductive success (sexual selection) often decrease its chances of survival. For example, the risks of injury and death can be high for males that fight for direct access to females or for territories that contain resources needed by females. Courtship ornaments and displays, which often determine territorial ownership or mating success, are not only energetically costly but frequently result in increased chances of predation. Some of the most striking and well-documented examples of the latter phenomenon involve reductions in sexual ornaments and modifications of behavior that reduce the conspicuousness of courting individuals in areas where predation is high compared with areas where predators are absent or uncommon (2, 3). These changes almost certainly increase survivorship at the expense of less effective territorial defense and lower mating success. In PNAS, Steinberg et al. (4) found that males of a semiarboreal lizard, the brown anole (Anolis sagrei), on islands in the Bahamas where a predator was introduced show a significant reduction in the amplitude of head bobs compared with lizards from predator-free islands. This behavioral change reduces the communication range of these visual signals, thus …