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University of Nottingham – Trophic engineering: the adaptive landscape of mechanical function in four-bar linkage systems of fish jaws – Dr Andrew MacColl

Project Objectives

Complex functional systems of living organisms can sometimes be well modelled from an engineering perspective. The ‘trophic’ (feeding) traits of fish provide a good example. They have been modelled as interacting systems of simple and four-bar linkage levers. In engineering design it is clear that there can be many-to-one mapping of form to function in such systems. This many-to-one mapping is also seen in the ‘design’ of organismal systems such as fish jaws which are arrived at through evolutionary processes. This can foster the evolution of diversity because different morphologies may have the same emergent functional properties, which cannot be differentiated by Darwin’s mechanism of natural selection. However, it is clear from existing work that organisms do not always occupy the full morphological ‘space’ of equivalent designs. In this project we will explore the extent of variation in the jaws of a rapidly evolving fish, the three-spined stickleback, modelled as four-bar linkage systems, and seek to understand the extent to which different populations of this fish vary, how that is related to the environments in which they live, and why they may forsake some areas of the functional parameter space that appear suitable from an engineering perspective.

Outcomes and benefits

The main research outputs of the project were:

The simulations developed by the student have already revealed interesting results. Previous work on the lever structures of fish jaws have used static measurements of jaw bones to derive conclusions about the way that these systems work, and have led to the idea that there is a hard trade-off between the speed and the force with which jaws close. The student’s dynamic simulations suggest that measurements of speed and force derived from static measurements may not closely resemble the true properties of fish jaws, and that the relationship between speed and force may be less of a constraint than previously thought. The simulation model developed by the student will continue to allow us to investigate the variation in jaw forms of three-spined stickleback.

The main benefits to the student were:

The student has had his first taste of working on an independent research project. He has developed a four-bar linkage simulation model of fish jaws, and incorporated published and new data into his simulations to reveal novel aspects of the dynamics of these systems. This has allowed him an insight to the way in which research is carried out in universities, and is likely to inform his choice of honours project.