Evolution of the chelicera: a dachshund domain is retained in the deutocerebral appendage of Opiliones (Arthropoda, Chelicerata)
Article first published online: 8 NOV 2012
© 2012 Wiley Periodicals, Inc.
Evolution & Development
Volume 14, Issue 6, pages 522–533, November/December 2012
How to Cite
Sharma, P. P., Schwager, E. E., Extavour, C. G. and Giribet, G. (2012), Evolution of the chelicera: a dachshund domain is retained in the deutocerebral appendage of Opiliones (Arthropoda, Chelicerata). Evolution & Development, 14: 522–533. doi: 10.1111/ede.12005
- Issue published online: 8 NOV 2012
- Article first published online: 8 NOV 2012
- NSF. Grant Number: IOS-0817678
The proximo-distal axis of the arthropod leg is patterned by mutually antagonistic developmental expression domains of the genes extradenticle, homothorax, dachshund, and Distal-less. In the deutocerebral appendages (the antennae) of insects and crustaceans, the expression domain of dachshund is frequently either absent or, if present, is not required to pattern medial segments. By contrast, the dachshund domain is entirely absent in the deutocerebral appendages of spiders, the chelicerae. It is unknown whether absence of dachshund expression in the spider chelicera is associated with the two-segmented morphology of this appendage, or whether all chelicerates lack the dachshund domain in their chelicerae. We investigated gene expression in the harvestman Phalangium opilio, which bears the plesiomorphic three-segmented chelicera observed in “primitive” chelicerate orders. Consistent with patterns reported in spiders, in the harvestman chelicera homothorax, extradenticle, and Distal-less have broadly overlapping developmental domains, in contrast with mutually exclusive domains in the legs and pedipalps. However, unlike in spiders, the harvestman chelicera bears a distinct expression domain of dachshund in the proximal segment, the podomere that is putatively lost in derived arachnids. These data suggest that a tripartite proximo-distal domain structure is ancestral to all arthropod appendages, including deutocerebral appendages. As a corollary, these data also provide an intriguing putative genetic mechanism for the diversity of arachnid chelicerae: loss of developmental domains along the proximo-distal axis.