The activity patterns of developmental genes correlate with the morphology of the cervical spine, as LMU scientists have shown. This discovery provides new insights into the genetic basis of evolution.
Archosaurs are an animal group that includes crocodiles and birds, but also the dinosaurs. Some archosaurs, such as the long-necked dinosaurs and today's birds, are very variable in the number and distribution of vertebrae in the spine. Both in the evolution of the birds and in the formation of the long-necked daurons the extension of the neck was an essential feature.
"In many cases, it is unclear how this variation came about. Especially in some dinosaurs there has been a long debate about the changes in the spine caused by shifts in individual vertebral areas, or by the addition of new elements, "says Christine Böhmer (Department of Geo-and Environmental Sciences of the LMU and Bavarian State Collection for Palaeontology and Geology) ). Together with Oliver Rauhut and Gert Wörheide (Department of Geo- and Environmental Sciences and Bavarian State Collection for Palaeontology and Geology) the team now examined whether the changes in the spine are also reflected in the activity patterns of certain developmental genes, the so-called Hox genes.
The main task of the Hox genes is to coordinate the formation of structures as superordinate choreographers during embryonic development. In this connection, they also play an important role in the formation of the spine and the distribution of the vertebrae in different areas of the spine. In the case of swirling, certain Hox genes are only active in certain body segments during development, so a characteristic expression pattern is found, which results in a sequence of strips within the embryonic tissue. "It was already known that these expression limits partly coincide with morphological boundaries in the spinal column, For example, the border between the cervical and vertebral vertebrae: a different group of Hox genes is responsible for the cervical vertebrae than for the vertebral vertebrae, "says Bohmer, the main author of the study.
Dino between crocodile and chicken
In a next step, the scientists investigated the morphology of the vertebras in the fossil long-binaurian plateosaurus, of which there are numerous very well-preserved fossils. "We found four different areas in the cervical spine, as in the case of the crocodile, but the second section was broadened, like the chicken," says Böhmer.
This suggests that an increase in the vertebral number in the second section of the cervical spine was the first step along the path of the evolution of the neck of the birds. "Accordingly, the expression patterns of the Hox genes have probably changed," says Böhmer. "Our results also suggest that the second step toward a longer neck is linked to the development of an additional section and the associated change in the genetic pattern observed in the chicken."
The scientists will now investigate further fossil animals in order to check whether Hox gene expression can also be reconstructed via the morphology of the vertebrae. "This, in turn, would allow us to draw conclusions about the mechanisms that have led to changes in the vortexes and thus to gain insight into the genetic basis of evolution, even in fossil animals such as dinosaurs, for which we, of course, have no direct genetic information "Says Böhmer.