DEVELOPMENT OF THE TAIL AUTOTOMY ADAPTATION IN LIZARDS UNDER DISPARATE LEVELS OF PREDATION AT HIGH AND LOW ELEVATIONS IN MEXICO

We measured relative predation pressure on lizard species at high and low elevations in south-central Mexico using (1) frequency of sighting s of potential predators, (2) survivorship of marked lizards, and (3) Schoener's index of predation intensity, which corrects for predator i nefficiency. All three measures indicated heavier predation at low com pared to high elevations. We measured length and thickness of tails an d the shear force required to elicit tail autotomy of species at both elevations. We analyzed our results in two ways: ignoring and includin g phylogenetic effects. The non-phylogenetic analysis of tail length i ndicated no clear relation between tail length and predation, but the phylogenetic analysis drew a clearer picture and showed that lizard sp ecies from low elevations under heavier predation had longer tails tha n those from high elevations with less predation, even after correctin g for phylogenetic constraints. Neither analysis identified a relation among tail thickness, phylogeny, and predation. Both analyses indicat ed that ease of tail autotomy was greater in lizard species from low e levations and heavier predation than in those from higher elevations w ith lighter predation. A distinct phylogenetic pattern to the force re quired to elicit tail autotomy was observed, and its relation to preda tion persisted even after correcting for phylogenetic constraints. One low elevation species, Sceloporus gadovae, is a tail autotomy special ist and thickens the original proximal tail base following tail autoto my. Subsequent autotomy of this thickened tail base occurs even more r eadily.