Meeting Abstract

12.4  Sunday, Jan. 4  Evolution of phalangeal formula in gymnophthalmid lizards: patterns of character states and inferences about developmental processes. GRIZANTE, MB*; KOHLSDORF, T; University of Sao Paulo, FFCLRP; University of Sao Paulo, FFCLRP tiana@usp.br

Limb reduction occurred repeatedly along Tetrapod evolution, and lizards in particular are one of the best models for studying the evolution of limblessness because intermediate forms are abundant and range from pentadactyl to entirely limbless. Recent studies suggest reversals in digit loss during the evolution of specific clades, but detailed investigation of the patterns of phalangeal formula evolution and possible developmental mechanisms underlying such morphological transitions is still urgently needed. Here we investigate in gymnophthalmid lizards if the patterns of limb reduction are common to the front and hind limbs, analyzing limb reduction in a phylogenetic context and inferring about possible developmental mechanisms related to digit loss in the group. Phalangeal formula and presence of limb bones and articulations were assessed from x-rays obtained from fixed specimens of microteiids available at the Museum of Zoology of the University of S Paulo. All analyses were performed based on a molecular phylogeny available for Gymnophthalmidae. Most tetradactyl species lack digit I, and lineages where one of the limbs is reduced usually retain the girdle, limb bones and even phalanges in the other limb. Moreover, digit loss seems to be decoupled between hand and foot in microteiids: some clades present major reduction in the hindlimb, while in others loss occurs mostly in the forelimb, and there is even one species that lacks different digits in the forelimb (d. I) and the hindlimb (d. V). The large plasticity of character states for phalangeal formula observed in Gymnophthalmidae likely lays on molecular mechanisms of developmental genes.