Movie above: the beginning of embryogenesis in the cricket Gryllus bimaculatus. Movie by Seth Donoughe from his paper on cricket embryonic development.

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.

Movie above: the middle stages of embryogenesis in the cricket Gryllus bimaculatus. Movie by Seth Donoughe from his paper on cricket embryonic development.

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.


The outcome of the developmental processes shown in the movies above is the body plan of the cricket Gryllus bimaculatus. Shown here is a sexually mature adult female.


Null hypotheses for developmental evolution. Church, S.H. and Extavour, C.G. Development, 147(8):dev178004 (2020). [PubMed]
Hox genes limit germ cell formation in the short germ insect Gryllus bimaculatus. Barnett, A.A., Nakamura, T. and Extavour, C.G.* PNAS, 116(33):16430-16435 (2019). [PubMed]
Expression and function of spineless orthologs correlate with distal deuterocerebral appendage morphology across Arthropoda. Setton, E.V.W., March, L.W., Nolan, E.D., Jones, T.E., Cho, H., Wheeler, W.C., Extavour, C.G. and Sharma, P.P. Developmental Biology, 430(1): 224-236 (2017). [PubMed]
Editorial Overview: Development, regulation and evolution of organ systems. Extavour, C.G. and Pick, L. Current Opinion in Insect Science, 13:vii-ix (2016). [PubMed]
The significance and scope of evolutionary developmental biology: a vision for the 21st century. Moczek, A., Sears, K., Stollewerk, A., Wittkopp, P., Diggle, P., Dworkin, I., Ledon-Rettig, C., Matus, D., Roth, S., Abouheif, E., Brown, F. Chiu, C.-H., Cohen, C.S., De Tomaso, T., Gilbert, S., Hall, B., Love, A., Lyons, D., Sanger, T., Smith, J., Specht, C., Vallejo-Marin, M. and Extavour, C.G. Evolution and Development, 17(3): 198-219 (2015). [PubMed]
Embryonic development of the cricket Gryllus bimaculatus. Donoughe, S. and Extavour, C.G. Developmental Biology, 411(1): 140-156 (2015). [PubMed]
A conserved genetic mechanism specifies deutocerebral appendage identity in insects and arachnids. B. Sharma, P. P., Tarazona, O.A., Lopez, D.H., Schwager, E.E., Cohn, M.J., Wheeler, W.C. and Extavour, C.G. Proceedings of the Royal Society B: Biological Sciences, 282(1808) 20150698 (2015). [PubMed]
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]