SEM Analysis of Turtle Embryogenesis
During the embryonic development of turtles anatomic structures are genetically instructed to develop in different orientations within an embryo. The analysis of a developing turtle embryo illustrates that the orientation of an anatomic structure is not caused by the making of new tissues, but rather a new arrangement of pre-existing tissues affecting the turtle’s morphology. The anatomical structural differences between turtles and other amniotes are mainly attributed to the positioning of ribs and pectoral girdle encased in the shell or rib cage in contrast to other tetrapods where the girdle is found outside the rib cage. Embryonic analysis during development has been reported in various model organisms, however, minimal analysis was done in these unique shelled vertebrates. Here we study comparative embryological similarities and differences between ancient and modern turtle species Chelydra serpentina (snapping turtle) and Chrysemys picta (painted turtle), further compared to the embryonic development of Gallus gallus (white Leghorn chicken). To this end analysis were performed using light microscopes and Scanning Electron Microscopes (SEM) in embryos of stages 12-28, thereby convincing the critical stages of development. These stages include development of somites, induction of carapace ridge, specification and differentiation of the carapace. Comparing the orientation of somites within snapping turtles have identified their development to be congruent to chickens. Also, the carapace ridge is formed at the interlimb level at stages 14-15 marking the step towards differentiating from chicken development. Comparing the developmental sequence of a structure in different organisms may provide insightful information about evolutionary changes and the origins of morphological characters.