BERGMANN, P.J.*; RUSSELL, A.P.; Tulane University, USA; University of Calgary, Canada: Patterns of variation in relation to tail morphology, vertebral number and tail length in lizards.

The number of caudal vertebrae can be highly variable in lizards. The question of whether this variability correlates with morphometric variability in terms of tail length is investigated. We also examined relative amounts of variation in the lengths of caudal vertebrae, standardizing comparisons by homologizing distal-most vertebrae between individuals. Six lizard species with divergent tail morphologies, relative lengths, scaling patterns, and functions were selected for investigation: Anolis grahami, Callisaurus draconoides, Calotes versicolor, Chamaeleo dilepis, Phrynosoma coronatum, and Pachydactylus turneri. In all but A. grahami, the number of caudal vertebrae correlated positively and highly significantly with relative tail length (0.3260 < R < 0.8028). Hence, changes in tail length resulting from selection are mediated, at least partially, through corresponding changes in vertebral number. Furthermore, in all species variance in relative length of caudal vertebrae was low along much of the tail, but increased dramatically at the distal end. This is suggestive of decreased levels of constraint on vertebral length at the distal end of the tail. Less stringent constraint on the distal portion of the tail implies that increases in tail length, whether by lengthening or addition of vertebrae, may occur preferentially in that region.