Geographic variation in antisnake tactics: The evolution of scent-mediatedbehavior in a lizard

We used modern comparative methods to examine the evolution of scent-mediat ed antisnake behavior in the rock-dwelling velvet gecko (Oedura lesueurii). The selective agent is a snake species (broad-headed snake, Hoplocephalus bungaroides) that feeds primarily on velvet geckos by remaining sedentary i n rock crevices for days or weeks, waiting to ambush lizards. The past and present distribution of this predator is well documented because of its thr eatened conservation status. We used this information to sample lizards fro m three populations distributed with snakes (sympatric) and three populatio ns that appear never to have been distributed with snakes (allopatric) in e ach of two widespread but geographically distinct genetic groups of velvet gecko (as determined using allozyme electrophoresis). Wild-caught immature geckos from sympatric populations showed higher tongue-hick rates and stron ger shifts in locomotion (increased duration of crawling and remaining stat ionary while pressed against the rock) toward snake-scented rocks than did lizards from allopatric populations. However, predation environment did not significantly affect a lizard's tendency to display other typical antisnak e tactics such as tail waving or fleeing. These results were highly repeata ble across the two sampled genetic groups of velvet gecko, despite demonstr able genetic divergence between groups. Experiments with hatchling lizards that had no experience with predators indicate that qualitative components of antisnake behaviors are probably inherited. The method of phylogenetical ly independent contrasts strongly suggests that the presence or absence of snakes has driven the evolution of behavior in velvet geckos. Collectively, these results provide support for an often suggested but speculative expec tation that prey can adapt to predation pressure on a local scale.