Evolution and Development of the Autopodium in Microteiid Lizard (Squamata: Gymnophthalmidae)

Abstract

The Gymnophthalmidae family of lizards has a Neotropical distribution and is characterized by great ecological and morphological diversity. This group brings together two lineages composed of species that exhibit different degrees of reduction in locomotor limbs, with the absence of several elements in the autopodium region (manus and pes) and evidence of reversal of the loss of digits in the genus Bachia. Limb reduction is a very frequent phenomenon in Squamata, and microteiid lizards represent an ideal group for studying genetic processes related to the reduction and loss of osteological elements in locomotor limbs. This family brings together two lineages with serpentine morphology, one with a predominant reduction in the front locomotor limbs (Gymnophthalmini) and the other with a reduction mainly in the rear locomotor limbs (Bachiini). The evaluation of genes expressed during the formation of locomotor limbs in the embryonic phase, including regulatory regions related to their control and regulation, makes it possible to evaluate the evolution of morphological diversity in the Gymnophthalminae family from a perspective that integrates evolution and development. Knowledge of genetic pathways related to the emergence of evolutionary novelties in certain clades, such as fossoriality in the group studied, enriches studies of evolutionary developmental biology (EvoDevo) by allowing the assessment of how evolutionary changes originate and are disseminated. The present research project aims to investigate genetic differences in developmental genes between species of Gymnophthalmini (reduction mainly of the forelimbs; e.g. Calyptomanus) and species of Bachiini (reduction mainly of the hind limbs; e.g. Bachia). Bioinformatics analyzes will be implemented focusing on genes involved in the formation and differentiation of locomotor limbs in the embryonic phase, such as Shh (Sonic Hedgehog), Gli3, Tbx4 and Tbx5, Ptx-1 and terminal Hox genes (with emphasis on clusters 'A' and 'D'), in addition to possible associated regulatory regions, such as enhancers and inhibitors described in the literature. The project is divided into three units: 1) Characterization of postcranial morphology in Gymnophthalmidae, focusing on locomotor limbs and associated structures, 2) identification and characterization of candidate genes in limb reduction processes in Gymnophthalminae; 3) study of the reversal of the loss of limb digits in the Bachia genus. The genetic regions of interest (candidate genes and regulatory regions) will be selected through bioinformatics analyzes (positive selection in coding regions and conservation analyzes of non-coding elements). The selected regions will be sequenced in species of Gymnophthalmini, Bachiini and pentadactile species of Gymnophthalminae and Teiidea (outgroup to Gymnophthalmidae). The study of reversion of digit loss in Bachia will be implemented through the sequencing of the complete genome of a lineage with reversal of digit loss (B. scolecoides or B. panoplia) and a species with the pattern of limb reduction (B bresslaui, B. dorbignyi or B. oxyrhina). The results will contribute significantly to the knowledge of the genetic bases related to the evolution of phenotypic diversity in Squamata, reinforcing the central role of EvoDevo in the process of expanding the Modern Synthesis of Evolution.