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X-ray CT analysis of evolutionary optimization of snake fangs
Author: Prof Anton du Plessis
Published: 22/10/2018
Mankind is often fascinated by spectacular natural structures, and sometimes we would like to learn how evolution converged to create such structures. Is the structure mechanically optimized for its basic task?

 

Snake fang evolution is one such interesting topic as venomous snakes provide an example of a fascinating pinnacle of the evolutionary process. Snake fangs are larger than normal teeth and are meant to deliver venom during a bite. This simple task has however evolved across all venomous species into not one but three basic shapes. 

The question is: is one of these three shapes optimized mechanically while the others are not? What are the driving forces in the shape optimization for these fangs?

This kind of biomechanical study sheds some new light on the pressures involved in the fang’s evolution. MicroCT is a 3D imaging technology which allows the viewing of internal details of objects non-destructively. Its use has grown over the last few years, and has been reviewed for its use in biological sciences [1]. Locally, this technology is available at the CT Scanner facility which provides microCT, nanoCT and 3D image analysis capabilities [2].

In the study reported in [3], the internal and external morphology of fangs were analysed in detail using nanoCT scans and biomechanical simulations were conducted using image-based simulation methods. This work comprised comparison of the results across approximately 20 fangs from different species.

The results indicate that of the various fang shapes that have evolved, none is superior to the other biomechanically – that means when one fang is longer and thinner, it has thicker walls to compensate, or when it is more curved it has a thinner venom canal, etc. The details of the morphology and the simulation details are reported in another paper [4].

An example is shown in the image above, the simulation is made by fixing the base (blue) and applying a load to the tip region (in green) – force direction indicated by the arrow. Linear elastic isotropic material properties are selected and the simulation is done using a direct finite element code based on microCT data. The resulting colours show areas of high stress as in the figure, in this case on the underside of the fang.

These simulations are not limited to biological structures and may be applied to any microCT data. It also finds application in engineering applications where the design files can be compared to the microCT data of the real parts, including rough surfaces and internal defects. The differences can then help to understand why a part fails or where the weakest point in the structure is. For more information please go to www.sun.ac.za/ctscanner

 

References:

    [1] A. du Plessis, C. Broeckhoven, A. Guelpa, and S. G. le Roux, "Laboratory x-ray micro-computed tomography: A user guideline for biological samples," Gigascience, vol. 6, no. 6, 2017.

    [2] A. du Plessis, S. G. le Roux, and A. Guelpa, "The CT Scanner Facility at Stellenbosch University: An open access X-ray computed tomography laboratory," Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms, vol. 384, 2016.

    [3] C. Broeckhoven and A. du Plessis, "Has snake fang evolution lost its bite? New insights from a structural mechanics viewpoint," Biol. Lett., 2017.

    [4] A. Du Plessis, C. Broeckhoven, and S. G. Le Roux, "Snake fangs: 3D morphological and mechanical analysis by microCT, simulation, and physical compression testing," Gigascience, vol. 7, pp. 1–8, 2018.

     

    As published in the 2017/2018 Annual Report (click here for the report)