The evolution of symmetry in echinoderms

Project Rationale

Symmetry is a fundamental property of the animal body plans that emerged over half a billion years ago, during the Ediacaran–Cambrian. While a few animal groups display radial symmetry or are asymmetrical, the vast majority are bilaterally symmetrical. However, determining why different types of symmetry evolved is challenging, in part because most phyla are characterized by only a single form. Echinoderms (starfish, sea urchins and their allies) are an exception; all modern species exhibit pentaradial (five-fold) symmetry, but the phylum also possesses an extensive fossil record that includes bilateral, asymmetrical and radial forms [1,2]. The aim of the proposed research is to investigate the evolution of symmetry in echinoderms as an exemplar for understanding the evolutionary significance of symmetry in animals more broadly. This will be achieved by studying the form, function and phylogeny of early fossil echinoderms using cutting-edge methods, including X-ray tomography, computational fluid dynamics and Bayesian inference. Furthermore, the ecology and environments inhabited by early echinoderms will be characterized and analyzed quantitatively using phylogenetic comparative methods. The results will transform our understanding of the evolution of symmetry in echinoderms, with broad implications for animal body plan assembly.

Methodology

A key first step in this project will be to construct a character matrix of extant and extinct echinoderms, incorporating morphological and molecular data, which will be analyzed with state-of-the-art phylogenetic methods. Virtual modelling and computational fluid dynamics [3] will then be used to analyze feeding performance in selected fossil echinoderms, informing on the function and ecology of forms with different types of symmetry. In addition, an extensive dataset characterizing the ecological (e.g. tiering, motility, feeding) and environmental parameters (e.g. water depth, oxygen, nutrient flux) of early echinoderms will be assembled and interrogated using phylogenetic comparative methods to determine whether trends in symmetry state evolution were driven by shared ancestry, ecology or environment. These analyses will be paired with studies of the spatial patterns of expression of key regulatory genes, thereby identifying the molecular and genomic basis for the echinoderm body plan.

Training

The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at the NHM. Specific training will include:

·        Taxonomy and systematics of early echinoderms

·        Assembling a database of ecological and environmental parameters from the literature

·        Phylogenetic analysis using Bayesian inference (MrBayes)

·        Phylogenetic comparative methods (R)

·        X-ray microtomography at µ-VIS X-ray imaging centre

·        3-D visualization (SPIERS)

·        Computational fluid dynamics (COMSOL Multiphysics)

·        In situ hybridization and immunohistochemistry