The proliferation of genomic resources for Chelicerata in the past 10 years has revealed that the evolution of chelicerate genomes is more dynamic than previously thought, with multiple waves of ancient whole genome duplications affecting separate lineages. Such duplication events are fascinating from the perspective of evolutionary history because the burst of new gene copies associated with genome duplications facilitates the acquisition of new gene functions (neofunctionalization), which may in turn lead to morphological novelties and spur net diversification. While neofunctionalization has been invoked in several contexts with respect to the success and diversity of spiders, the overall impact of whole genome duplications on chelicerate evolution and development remains imperfectly understood. The purpose of this review is to examine critically the role of whole genome duplication on the diversification of the extant arachnid orders, as well as assess functional datasets for evidence of subfunctionalization or neofunctionalization in chelicerates. This examination focuses on functional data from two focal model taxa: the spider Parasteatoda tepidariorum, which exhibits evidence for an ancient duplication, and the harvestman Phalangium opilio, which exhibits an unduplicated genome. I show that there is no evidence that taxa with genome duplications are more successful than taxa with unduplicated genomes. I contend that evidence for sub- or neofunctionalization of duplicated developmental patterning genes in spiders is indirect or fragmentary at present, despite the appeal of this postulate for explaining the success of groups like spiders. Available expression data suggest that the condition of duplicated Hox modules may have played a role in promoting body plan disparity in the posterior tagma of some orders, such as spiders and scorpions, but functional data substantiating this postulate are critically missing. Spatiotemporal dynamics of duplicated transcription factors in spiders may represent cases of developmental system drift, rather than neofunctionalization. Developmental system drift may represent an important, but overlooked, null hypothesis for studies of paralogs in chelicerate developmental biology. To distinguish between subfunctionalization, neofunctionalization, and developmental system drift, concomitant establishment of comparative functional datasets from taxa exhibiting the genome duplication, as well as those that lack the paralogy, is sorely needed.
The comparative embryology of Chelicerata has greatly advanced in recent years with the integration of classical studies and genetics, prominently spearheaded by developmental genetic works in spiders. Nonetheless, the understanding of the evolution of development and polarization of embryological characters in Chelicerata is presently limited, as few non-spider species have been well studied. A promising focal species for chelicerate evo-devo is the daddy-long-legs (harvestman)
We present a staging system of
Considering the phylogenetic position of Opiliones and the unduplicated condition of its genome (in contrast to groups like spiders and scorpions), this species is poised to serve as a linchpin for comparative studies in arthropod development and genome evolution. The staging system presented herein provides a valuable reference for
- Award ID(s):
- 2016141
- NSF-PAR ID:
- 10363405
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- Frontiers in Zoology
- Volume:
- 19
- Issue:
- 1
- ISSN:
- 1742-9994
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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