Speed versus manoeuvrability: association between vertebral number and habitat structure in lacertid lizards

Abstract

We tested the hypothesis that the number of presacral vertebrae in lacertid lizards has evolved to meet requirements set by the structural habitat. The idea was that lizards from cluttered habitats (densely vegetated areas, stony walls and hills, rocks) would be aided by a flexible backbone with many vertebrae, ensuring manoeuvrability, whereas lizards from open habitats would require stiffer vertebrate columns, with relatively few vertebrae, favouring speed and acceleration capacity. In contrast to earlier findings in fishes and snakes, evolution of vertebral number and body size was uncorrelated in lacertid lizards. Body size also did not differ between structural habitat types (open areas, densely vegetated areas, vertical elements). Traditional analysis of variance suggests strong differences in vertebral counts between species from open areas and cluttered areas, the latter having higher numbers of presacral vertebrae. When adequate phylogenetic analyses are used, differences remain significant although the level of significance is considerably lower. Tests of the mechanistic relationships between vertebral number, bending ability, and manoeuvrability, and assessment of the relative importance of manoeuvrability and speed in habitats with varying degrees of impediment are needed to reveal the evolutionary path that has led to the differences in vertebral number.