Collaborative Research: Integrating Phylogenomics with the Fossil Record: Sea Urchins as a Model Clade for Macroevolutionary Research

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Spine-covered, globular sea urchins are iconic marine animals common in kelp forests and coral reefs, where they are often the main consumers of algae and other organisms. By contrast, sand dollars are extremely flattened urchins that generally live buried in sandy seafloors, feeding by picking tiny particles of food from the sediment. Multiple lines of evidence suggest these two groups are closely related, originating from an ancestor whose body form and ecology were broadly similar to those of modern sea urchins. This suggests a striking contrast in evolutionary pathways: while some lineages have barely changed over hundreds of millions of years, others have innovated dramatically. Identifying the mechanisms that underlie these different trajectories is necessary to understand the processes generating and maintaining biological diversity. However, doing so requires accurate reconstructions of events that took place in the deep past, and integrating genomic, morphological, and paleontological information. The project highlights these charismatic animals as models for studying evolutionary change in a variety of outreach modes including undergraduate research programs, teacher workshops, and displays in public museums.The project focuses on developing phylogenomic resources to improve our knowledge of evolutionary relationships among living sea urchins, sand dollars and allies (collectively known as echinoids). Given the clade’s outstanding fossil record, these data will be combined with morphological and stratigraphic information using a total-evidence dating approach, allowing all major lineages of living and fossil echinoids to be placed in a common, time-calibrated tree of life. Using phylogenetic comparative methods, the project will reveal evolutionary processes associated with the origins of both irregular echinoids and sand dollars, two major events in body-plan innovation. Analyses will rely on a large-scale dataset of echinoid body measurements to explore changes in evolutionary rate and modularity, and correlate shifts in these metrics with known events of developmental innovation and ecological specialization. The contributions of ecological, developmental and morphological traits to speciation and extinction dynamics will be assessed using state-dependent models of diversification. Finally, ontology-informed ancestral state reconstructions will help identify the number of independent origins (and losses) of the sand dollar morphotype, as well as the relative timing of these events. By combining recent developments in phylogenomics and phylogenetic paleobiology, this project will establish echinoids as a model clade in macroevolutionary research.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.