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SATELLITE SYMPOSIUM #1 2007

Craniofacial Development and Evolution

 

ABSTRACTS


The genetic and developmental basis of cichlid trophic diversity

R. CRAIG ALBERTSON
Department of Biology, Syracuse University

Lake Malawi cichlids have undergone a spectacular radiation in feeding morphology, making them an ideal model to study the factors that underlie craniofacial diversity. Here we explore the genetic and developmental mechanisms that underlie this remarkable divergence in craniofacial architecture. Quantitative genetic analyses show that the cichlid feeding apparatus is regulated by few genes of large effect, and is composed of modules that have evolved under strong directional selection. Comparative embryology reveals that adaptive variation in cichlid jaw shape is evident early in development, and potentially regulated by bmp4. Modulating this growth factor in the experimentally tractable zebrafish model reproduces natural variation in cichlid jaw shape, supporting a role for bmp4 in craniofacial evolution. These data highlight the utility of the cichlid jaw as a model for studying the genetic and developmental basis of evolutionary changes in craniofacial morphology.

 


Regulation of agnathan Dlx genes

KYLE J MARTIN, A MAURYA, S KURAKU, S KURATANI AND M EKKER
Department of Biology, University of Ottawa, Ottawa, ON

Dlx genes are required for the development of gnathostome novelties including paired appendages and jaws. In the branchial arches, the nested expression of 6 Dlx genes specifies intra-arch identity and patterns their dorsal-ventral axis. Lampreys do not appear to completely share this expression pattern. Dlx gene regulation is linked with their conserved genomic organization into 3 bigene clusters. Enhancer elements, particularly within the intergenic region, have been shown to regulate gnathostome Dlx expression, but none have been identified in agnathans. We report the presence of 6 Dlx genes in lampreys and show that at least two are organized in a bigene cluster. We also identify 3 Dlx genes in hagfish, including one bigene cluster. Using phylogenetic footprinting and transgenic assays we search for regulatory elements in agnathan Dlx loci.

 


Are all vertebrate scleral ossicles homologous to one another?

TAMARA FRANZ-ODENDAAL
Biology Department, Mount Saint Vincent University, Halifax, NS

Scleral ossicles are small plates of bone situated within the sclera of the vertebrate eye. Although these elements are present in many vertebrates, they are not the same in every vertebrate. Within reptiles, scleral ossicles are numerous in number (6-16 elements per eye) and overlap one another to form a sclerotic ring. These ossicles are neural crest derived and develop intramembranously, via an epithelial-mesenchymal induction. In fish, scleral ossicles are fewer in number (1-2 per eye), do not contact one another and develop endochondrally. These bones may not be homologous to one another, despite their same name. The development and evolution of these elements will be discussed.

 


Cranial crest ontogeny on lambeosaurine dinosaurs

DAVID EVANS
Dept. of Natural History, Royal Ontario Museum, Toronto, ON

Lambeosaurinae is a monophyletic clade of large herbivorous ornithischian dinosaurs characterized by hypertrophied nasal passages housed within distinctive cranial crests. Excellent cranial ontogenetic series are known for four closely related taxa from Alberta, Canada: Corythosaurus casuarius, Lambeosaurus lambei, Hypacrosaurus altispinus and H. stebingeri. Juveniles of all taxa have similar incipiently developed crests, and diverge in crest morphology during the active phase of crest growth. Differences in crest growth in these taxa are investigated using qualitative comparisons and morphometric analyses. The first species-level hypothesis of lambeosaurine interrelationships allows initial exploration of crest heterochrony within the clade.

 


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