EVOLUTION OF AXIAL SKELETAL REGIONALISATION IN VERTEBRATES: INTEGRATING PHYLOGENY, ENVIRONMENT, AND DEVELOPMENTAL MECHANISMS

Evolutionary diversification of the axial skeleton (i.e. vertebrae and ribs) is a key component of the success of vertebrate animals. "Fishes" are generally thought to possess a two-region axial skeleton, with "precaudal" and "caudal" vertebrae, while tetrapods exhibit regionalisation of their vertebral column into distinct cervical, thoracic, sacral, and caudal regions. Conventional wisdom is, therefore, that the evolutionary transition from water to land coincided with increasing anatomical specialisations of the vertebral column. However, recent discoveries of striking axial skeletal complexity in some living and fossil fish groups suggest an alternative scenario: the primitive presence of a regionalised, complex axial skeleton in vertebrates, with repeated loss or augmentation of regionalisation as adaptation to new environments and ecologies. This project will be the first to explicitly and quantitatively reconstruct the evolutionary history of vertebrate axial skeletal complexity, and to test for environmental and developmental correlates of such complexity.

In order to understand the evolution of the vertebral column and its role in diversifications into new environments and ecology, we will combine anatomical and regulatory genetic datasets to undertake a concerted investigation of axial skeletal regionalisation in a broad taxonomic sample of extant and fossil vertebrates. 1) We will quantify axial skeletal regionalization and complexity based on skeletal data derived from Computed Tomography and direct specimen measurement. 2) We will use comparative phylogenetic methods to reconstruct ancestral states for major vertebrate clades and to test for correlations between axial skeletal regionalisation and environmental and ecological factors. 3) We will test for expression of genes that define the amniote cervical-thoracic and thoracic-lumber transitions in embryos of a cartilaginous fish (the skate, Leucoraja erinacea), and we will use fluorescent cell labelling approaches to test whether these genes delineate previously unrecognised axial skeletal regions in this species. By comparing our findings with those from other lineages (e.g. tetrapods), we will be able to infer mechanisms of axial skeletal development at one of the earliest nodes in vertebrate evolutionary history. 4) Finally, we will use evolutionary modelling to combine results of anatomical, evolutionary, and developmental analyses to elucidate the relationships between vertebral morphology and developmental mechanisms in evolutionary transitions into new environments.

Debate surrounding the evolution of the vertebrate axial skeleton has lingered for centuries, with current dogma and "textbook scenarios" stemming largely from speculation, and suffering from poor taxon sampling. Our study will integrate anatomical, developmental and environmental data, within a rigorous phylogenetic framework, in order to accurately reconstruct the evolutionary and ecological history of the vertebrate axial skeleton.

This project is the first integration of fossil and extant anatomy with Hox expression patterns in a comparative phylogenetic framework across Vertebrata. The complimentary skill sets of the investigators make them uniquely suited to successfully conduct this research, and results will have broad impact on NERC user groups including the general public, students, and researchers (see Academic Beneficiaries).

The researcher co-investigator: The project will provide the Res-CoI, Katharine Criswell, with excellent opportunities for honing transferable skills in project management, networking, team-working, and written and verbal communication. She will also develop skills in bioinformatics, computational biology, statistics and experimental embryological techniques.

The general public: The research proposed here is uniquely positioned to directly educate the general public through exhibition and outreach in the University Museum of Zoology. We will incorporate results of this project in the museum exhibit structure through flexible exhibit space (1500 ft2) for a projected viewership of 100,000/year. The exhibit will also be available for temporary travel to other museums. Thus, through public display, products of this project will educate both the general public and biodiversity decision-makers. We will additionally develop curriculum materials on vertebrate evolution based on this project for the Museum's educational outreach programs to area schools.

There is tremendous public interest in evolutionary transitions recorded in the fossil record and extant anatomy (e.g., the transition of vertebrates from water to land, the origin of snakes, the evolution of sharks, evolution of extreme body sizes), and a major focus of this project is on axial skeletal evolution in these events. Additionally, chondrichthyan fishes (sharks, skates, rays) have tremendous public appeal, and studies using chondrichthyan embryos as a model for understanding animal evolution have garnered considerable popular media attention. For example, previous work by the CI on chondrichthyan skeletal development has been the topic of media coverage in The Times, National Geographic, Washington Post, USA Today, MSNBC, IFL, and Discovery Channel. This research therefore presents an exceptional opportunity to convey the importance of evolutionary and developmental biology research to the general public. Our public demonstrations on shark and skate embryology during Cambridge Science Week's "Science on Saturday" are very popular, and receive considerable attention from both adults and children. We will use the Cambridge Science Festival to test a new and improved demonstration on chondrichthyan biology. A new addition to this demonstration will be live shark embryos (to be purchased from the Station Biologique in Roscoff). We would repeat this demonstration during future Science Festivals and at local schools.

Cambridge Musculoskeletal Sciences Network (CMSN): The CMSN is an interdisciplinary research network that spans the University of Cambridge, and that operates at the interface of biological and physical sciences, technology and clinical medicine to promote musculoskeletal research with translational potential. AG has previously used CMSN functions as a venue for identifying and communicating basic aspects of fish skeletal biology that may have such potential, and will continue to do so with this research.

Undergraduate student researchers: The Department of Zoology, University of Cambridge offers extensive research opportunities to undergraduates as part of degree requirements. Research components of this proposal are amenable to student participation at all academic levels, and students will be able to participate in data acquisition and analysis, as well as devising new research from the outlined deliverables. Research availability for students will facilitate the outlined objectives as well as allow the Res-CoI to develop mentoring skills.