Although the insect body plan is well conserved, the developmental mechanisms of body patterning are surprisingly varied. The fruit fly Drosophila melanogaster has long served as a model organism to investigate the molecular mechanisms regulating embryonic axial patterning, long germ segmentation (in which all body segments are established near-simultaneously), and acquisition of specific body region and segment identities. However, basally branching insects and other arthropods develop their segments in a sequential fashion, similar to non-insect arthropods and to vertebrates. The arthropod body plan, including appendage development, has also undergone extensive evolutionary modifications in different clades.

We have studied the evolution of the underlying genetic mechanisms that result in the differences in arthropod body patterning using a number of model organisms and developmental processes. These include segmentation in the cricket Gryllus, appendage development in daddy longlegs, and Hox genes in scorpions. In the process, we have helped collaborator Prashant Sharma (American Museum of Natural History) develop the harvestman Phalangium opilio into the first daddy longlegs model laboratory system suitable for functional genetic analysis.


Hox gene duplications correlate with posterior heteronomy in scorpions. Sharma, P.P., Schwager, E.E., Extavour, C.G. and Wheeler, W.C Proceedings of the Royal Society B: Biological Sciences, 281(1792): 20140661 (2014). [PubMed]
Subdivision of arthropod cap-n-collar expression domains is restricted to Mandibulata. Sharma, P.P., Gupta, T., Schwager, E.E., Wheeler, W., and Extavour C.G EvoDevo, 5(1): 3 (2014). [PubMed]
Distal-less and dachshund pattern both plesiomorphic and derived structures in chelicerates: RNA interference in the harvestman Phalangium opilio.. Sharma, P.P., Schwager, E.E., Giribet, G.G., Jockusch, E. and Extavour, C.G Evolution and Development, 15(4): 228-242 (2013). [PubMed]
Evolution of the chelicera: a dachshund domain is retained in the deutocerebral appendage of Opiliones (Arthropoda, Chelicerata). Sharma, P.P., Schwager, E.E., Extavour, C. G. and Giribet, G Evolution and Development, 14(6): 522-533 (2012). [PubMed]
Hox gene expression in the harvestman Phalangium opilio reveals divergent patterning of the chelicerate opisthosoma. Sharma, P.P., Schwager, E.E., Extavour, C. G. and Giribet, G. Evolution and Development, 14(5): 450-463 (2012). [PubMed]
Notch/Delta signalling is not required for segment generation in the basally branching insect Gryllus bimaculatus. Kainz, F., Ewen-Campen, B., Akam, M. and Extavour, C.G. Development, 138(22): 5015-5026 (2011). [PubMed]