Browsing by Subject "developmental biology"

The skull represents the most highly diversified and evolutionarily adapted anatomical aspect of metazoans, and its development and evolution have been a major driving force in the expansion of vertebrates. The evolution of skull and lower jaw bones have led to the adaptive radiation of jawed vertebrates, and skull tissues have changed rapidly over time and were finely tuned to meet functional and ecological demands with tremendous precision. Because of the long-lasting interest in conventional animal models, there is no general genetic or developmental model of skull evolution and diversity in vertebrates. Squamate reptiles represent the best model to study those aspects because of their key basal phylogenetic position within amniotes (i.e., mammals, birds, reptiles) and their exceptionally high levels of morphological variation (including their kinetic skulls). In particular, their lower jaw bones display tremendous variation. In order to assess this variation and the ecological and developmental factors connected to it, several methods from different fields of biology have to be used. In this study, morphometric, embryology and developmental approaches are used to investigate the ecological and developmental factors associated with the diversification of lower jaw bones in snakes and lizards. The shape diversity of squamate lower jaw bones was approached in a systematic way, using geometric morphometrics. Embryological methods were used to compare the embryonic stage of available squamate model animals at oviposition and to assess the order of ossification of embryo with earliest developmental stage at oviposition (bearded dragon, Pogona vitticeps). In addition, expression of major conserved candidate genes at different stages of lower jaw development (pharyngeal arches, mesenchyme patterning, ossification) were assessed in this species. The results indicate that the lower jaw bones of snakes versus lizards but also of fossorial squamates versus other habitats are significantly different. Heterochrony was also detected at both early stages (pharyngeal arche development at oviposition) and at the onset of ossification in lizards and snakes. Coherent with that, alterations in the expression pattern of Dlx genes in pharyngeal arches were observed in bearded dragon in comparison to earlier studies with mice, while other conserved markers of skeletogenesis were rather conserved. This analysis of the genotype and phenotype map of the reptilian skull provides some new insights into the development, origin and divergence of vertebrate tissues. The results will establish a good basis for future studies involving comparative developmental biology of bearded dragon. Future studies will offer excellent new opportunities to link craniofacial morphology, genetics/genomics and development to both ecological adaptation and evolutionary biology.