Correlated evolution of herbivory and food chemical discrimination in iguanian and ambush foraging lizards

To efficiently locate and assess foods, animal sensory capacities and behavioral discriminations based on them must be appropriate for the diet and method of hunting. In lizards, actively foraging insectivores identify animal prey using lingually sampled chemical cues, but ambush foragers do not. Among plant eaters derived from active foragers, plant chemical discrimination is added to prey chemical discrimination, resulting in correlated evolution of plant diet and plant chemical discrimination. Here I present comparative evidence on the relationships between plant diet and food chemical discrimination in Iguania, which consists primarily of ambush foragers and is one of two major lizard clades, and for ambushing lizards in general. Comparative analyses conducted using phylogenetic methods show that (1) all but one species of omnivore studied exhibited both prey and plant chemical discrimination, whereas ambush foragers exhibited neither; (2) significant correlated evolution occurred between plant diet and plant chemical discrimination in Iguania and in omnivores and herbivores derived from ambush foragers; and (3) correlated evolution has occurred between prey and plant chemical discrimination in Iguania and, more generally, in taxa derived from ambush foragers. These results are explained by selection on plant eaters to assess the nutritional value and possible toxicity of plants and by continued consumption of some animal prey even in herbivores combined with freedom from factors that select against prey chemical discrimination in ambush foragers. Copyright 2003.