The rise of vertebrate necks: how salamanders use the spine in feeding

Description

Background and Motivation

The tetrapod neck is a major evolutionary transformation critical for the evolution of terrestrial vertebrates (tetrapods) from aquatic fishes. This specialized region of the spine spans the gap between the skull and the shoulder (pectoral) girdle and allows the head to move three-dimensionally and independently of the body. A mobile neck is agreed to be one key factor in the colonisation of land by stem tetrapods. But how the neck contributed to new feeding behaviours and the water-to-land transition are still unknown. Current hypotheses about the function and evolution of the tetrapod neck are based on anatomical studies, but the correlation between neck anatomy, mobility, and feeding motions is untested. This is due to the lack of data on 3D neck motions in living animals, as the spine’s motion is complex and invisible externally. We will use salamanders as living models of early tetrapod feeding, as they share anatomical features of the feeding apparatus and neck, transition between land and water, and change their feeding anatomy throughout development.

Study Hypothesis

We hypothesise that the neck and anterior vertebrae have vital roles in salamander feeding. Your project will test two sub-hypotheses:

H1. In salamanders only the anatomically distinct vertebrae (forming a morphological neck) rotate to move the head (forming a functional neck).

H2. The identity and feeding motions of the “functional neck” can be predicted from vertebral shapes and maximum intervertebral joint mobilities across salamander species.

Objectives

1. Measure the 3D motion of the vertebral column during feeding in live salamanders to determine which vertebra form the ‘functional neck’. You will use a dataset of previously collected x-ray videos of salamander feeding, and collect computed tomography (CT) scans to generate digital bone models. You’ll be trained to combine these into a 3D skeletal animation using X-ray reconstruction of moving morphology (XROMM). Your results will provide the first measurements of neck motion in live salamanders, revealing their role in feeding.
2. Determine the maximum possible range of motion (RoM) of the intervertebral joints in salamanders. You will collect CT scans and biplanar x-ray videos of cadaveric specimens of 5 salamander species, physically manipulating each to express the maximum possible motion of the intervertebral joints. By creating XROMM animations, you will measure the RoM of each intervertebral joint and compare RoM along the spine and among species. Your results will help evolutionary morphologists and biomechanists reconstruct extinct species and understand vertebral regionalisation.
3. Compare the anatomy of the vertebrae within and among 5 salamander species and relate them to the feeding motions and RoM of each species. You will analyse digital bone models to quantify the shape of each vertebra and how that shape changes across the spine and among species. How is the spine separated into anatomically distinct regions in these salamanders? And do anatomical regions correspond with regions of distinct RoM (Obj. 2) and feeding kinematics (Obj. 1)? Your results will provide an integrated view of the morphology, joint mobility, and feeding motions of the vertebral column.

Significance

Your project provides much-needed data on neck motion in living animals to test long-standing hypotheses about the origin and evolution of land-dwelling vertebrates. Establishing these structure-function relationships in living salamanders will inform reconstructions of possible neck motions in extinct stem tetrapods. More broadly, you will reveal how the spine contributes to feeding motions. While the neck and body are acknowledged to influence feeding functions, most feeding studies stop at the back of the head. You will examine head and spine motion to better understand the form and function, evolution, and biomechanics of vertebrate feeding.

Training opportunities

You will:

-learn a wide range of skills in biological imaging analysis, digital modelling and animation, quantitative morphology, and evolutionary biology

-have a mix of team- and independent-projects

-have the opportunity to present your research at conferences

-international travel and networking, with collaborators in Germany and Belgium

-be joining a community of researchers in the Evolutionary Morphology and Biomechanics group at University of Liverpool

Essential Applicant Qualifications

You need to have:

• Enthusiasm for learning about neck kinematics and 3D computer visualization
• Creative and interdisciplinary problem-solving skills
• Strong written and interpersonal communication

Desirable Applicant Qualifications

It is helpful—but not require if you also have any of the following:

• Familiarity with vertebrate anatomy and physiology
• Experience with biological imaging (e.g., image analysis, 3D reconstruction, motion tracking)
• Experience in biomechanics (applying mechanical or engineering principles to biological structures and motions) or other interdisciplinary work.

If you have any questions or would like to discuss this project informally, please email Ariel Camp (Ariel.camp@liverpool.ac.uk)

Supervisors: 

Ariel Camp - ariel.camp@liverpool.ac.uk

Daniel Schwarz - daniel.schwarz@smns-bw.de

Peter Falkingham - P.L.Falkingham@ljmu.ac.uk

Kris D’Aout - kdaout@liverpool.ac.uk