Desenvolvimento embrionário e pós-natal de Tropidurus torquatus wied, 1820 (squamata : tropiduridae) : estágios embrionários e ontogenia do esqueleto

Abstract

Developmental studies are an important contribution to the interpretation of evolutionary patterns responsible for extant phylogenetic lineages. Squamates are a highly diverse group that is still underrepresentated in embryological investigations. The present study describes the sequence of in ovo development of Tropidurus torquatus. Gravid females were collected by noose in antropized surroundings of Brasília, Brazil, and maintained in terrariums until oviposition. Once deposition occurred, eggs were transferred to a 30ºC (± 0,1º C) temperature incubator. Daily collection of embryos were accomplished from oviposition to hatching, which took place after approximately 75 days, resulting in a total of 209 embryos obtained in two reproductive seasons. Fifteen developmental stages were established based on external morphological characteristics widely used in lizard literature such as visual structures, pharyngeal arches, facial primordial fusion, limb development, pigmentation and scales.Organogenesis was already in progression at the moment of oviposition, at which embryos resemble stage 28 of other studies. Comparisons with other lizards show a conserved embryonic sequence, however developmental timing differences were found in features such as the pharyngeal arches, endolymphatic sacs, pigmentation and scales.The order of T. torquatus fore-and hindlimb formation differs from that most commonly observed in lizards. The development of the phallic and cranial lip of the cloaca anlages are compared with that of other lizards. The adult skeleton of T.torquatus was describes and served as a guide for the developmental descriptions. The chondrocranium of T. torquatus presented reduction of orbitotemporal elements such as the teania marginalis and pila antotica. Dermal elements apparently show a conserved ossification sequence amongst lizards, main variations occurring in the ossification sequence of chondral elements. Vertebrae ossify in a cranial-caudal gradient, but are dissociated from the ossification of the ribs which do not follow this gradient. An independent center of ossification for the sacral and caudal ribs was not visualized. In the limbs, a continuous cartilaginous condensation forming a "Y" was first seen, followed by the development of the limb understructure which consists in the formation of the primary axis and the digital arch. The autopodial elements of the hindlimbs developed slightly earlier than the forelimbs. All distal carpals were seen, distal carpal I remaining in close contact with its metacarpal. The dcV did not show an embryonic connection with dcIV. In regard to the distal tarsals, only the chondrogenic condensation of distal tarsal I was not visualized. We found an embryonic connection between distal tarsal V and distal tarsal IV, indicating that dtV is probably not a de novo condensation. The distal tarsal II and V consisted in transitory condensations that rapidly fused with their respective metatarsal. Three chondrogenic elements were identified as constituents of the tarsus: fibular,...