Developing an integrated understanding of the evolution of arthropod segmentation using fossils and evo-devo

Abstract

Segmentation is fundamental to the arthropod body plan. Understanding the evolutionary steps by which arthropods became segmented is being transformed by the integration of data from evolutionary developmental biology (evo-devo), Cambrian fossils that allow the stepwise acquisition of segmental characters to be traced in the arthropod stem-group, and the incorporation of fossils into an increasingly well-supported phylogenetic framework for extant arthropods based on genomic-scale datasets. Both evo-devo and palaeontology make novel predictions about the evolution of segmentation that serve as testable hypotheses for the other, complementary data source. Fossils underpin such hypotheses as arthropodization originating in a frontal appendage and then being co-opted into other segments, and segmentation of the endodermal midgut in the arthropod stem-group. Insights from development, such as tagmatization being associated with different modes of segment generation in different body regions, and a distinct patterning of the anterior head segments, are complemented by palaeontological evidence for the pattern of tagmatization during ontogeny of exceptionally preserved fossils. Fossil and developmental data together provide evidence for a short head in stem-group arthropods and the mechanism of its formation and retention. Future breakthroughs are expected from identification of molecular signatures of developmental innovations within a phylogenetic framework, and from a focus on later developmental stages to identify the differentiation of repeated units of different systems within segmental precursors.

The common house spider Parasteatoda tepidariorum

“…This segmentation mode contrasts with that of Drosophila, but is widely observed in arthropods, including many non-Drosophila insects. The cellular and molecular events at the posterior terminal region, as well as the presumptive head region of the forming or elongating germ band, in Parasteatoda attract researchers who seek to understand the evolution of arthropod segmentation [9][10][11][12][13][14][15].…”

Development of the Pre-gnathal Segments in the Milkweed Bug Oncopeltus fasciatus Suggests They Are Not Serial Homologs of Trunk Segments

“…Arthropods are a hyper-diverse animal phylum characterized by both high species numbers and exceptional biomass. One of the reasons for their immense success is believed to be their segmented body plan, which provides high evolvability via a modular organization (Chipman and Edgecombe, 2019).…”

New opabiniid diversifies the weirdest wonders of the euarthropod lower stem group

“…5c ), support a single origin of arthropodization in euarthropods. A possible developmental framework would entail the single anterior protocerebral pair of arthropodized limbs in radiodonts becoming co-opted posteriorly to enable the arthropodization of all limbs (Jockusch, 2017; Chipman and Edgecombe, 2019). This scenario would require the convergent fusion of presumed protocerebral appendages in opabiniids to form a single proboscis, and of protocerebral limb buds in deuteropods to form the labrum (Chipman, 2015; Jockusch, 2017; Ortega-Hernández, Janssen and Budd, 2017; Park et al , 2018).…”