DEFENSIVE HORN RAISING BY HORNED LIZARDS (PHRYNOSOMA): A UNIQUE BEHAVIORAL RESPONSE IN PHRYNOSOMATID LIZARDS?

摘要

Our study adds an additional species of horned lizard, Phrynosoma ditmarsi, to seven other species (in three clades) found to have horns-raised and back-arched responses to cranial tactile pressures exerted by human fingers simulating a snake ingestion grasp. In contrast to these members of the subfamily Phrynosomatiae, we also tested a species in a different tribe (Callisaurini), Callisaurus draconoides, and a species of a different subfamily (Sceloporinae), Sceloporus magister, of nonhorned phrynosomatid lizards for similar responses. We conclude that horned members of the subfamily Phrynosomatinae (Phrynosoma) exhibit these probable antipredator responses but that these behavioral responses are lacking in the nonhorned members of the family. The horns-raised and back-arched behavioral responses are exhibited throughout the genus, even in species with the smallest horns. Like horns, they are plesiomorphic for the genus. Horn development is positively allometric but horns may have undergone developmental reversal in size in two clades. In addition, we note perhaps convergent aspects of head-positioning antipredator defense behaviors, coupled with distinctly different morphological features, within the genus Phrynosoma and Moloch horridus.