Jump to content
Powered by

Sharks and the evolution of the locomotory apparatus

Zoologists at the University of Tübingen are investigating the biomechanics of swimming and the evolution of the muscles and tendons needed for swimming. Detailed information on how fish adapt to specific lifestyles help in the development of robot fish.

A tasty research object: Prof. Dr. Sven Gemball with a big bonito [Sarda sarda (Bloch, 1793)] , caught during a marine biology course in Catalonia in 2007. (Photo: University of Tübingen)
Nature has frequently been used as a model for artificial constructs. Marine organisms are also inspiring the work of engineers, for example engineers developing swimming robots that are used to investigate the oceans. After all, fish have many years of experience in moving around in water and have optimised their locomotory apparatus in many versatile ways as they evolve. Prof. Dr. Sven Gemballa is keeping future applications in mind, but is concentrating on basic research in order to create a substantial knowledge base.

For many years Gemballa has been doing research on the site to which the muscle fibres of the locomotory apparatus attach and he has discovered previously unknown features: “It was long assumed that the attachment areas with their complex folds had a homogenous connective tissue structure, and were a kind of cement that held the muscle segments together,” said Gemballa. Gemballa and his team developed a new combination of techniques that enabled them to visualise the three-dimensional morphology of the myosepta, as the muscle fibres are called, that are separated by sheets of connective tissue (the myosepta). The researchers discovered that there is much more to this complex structure than previously assumed.

Surprising discovery: tendons are important for swimming

“In the middle of the 1990s, I was able to show that the attachment areas consist of a complex system of flexible tendons. The parallel myoseptal tendons are able to transmit previously generated muscular forces,” said the researcher with well-deserved pride. Once it became clear that these structures were important for swimming, Gemballa commenced comparative investigations.
Gemballa is investigating how the tendons developed during evolution. Several years ago during his doctorate, Gemballa carried out comparative investigations between basal fish groups such as bichirs and gars and the more distantly related snakeheads. The feature that the three groups have in common is that they live in similar ecological niches and are lurking freshwater predators. Gemballa succeeded in showing that they also had similar tendon structures. The first investigations were followed by the investigation of the tendon system in all representatives of all major groups of cartilaginous fish (Chondrichthyes) and bony fish (Osteichthyes)

How did the structures diversify?

According to current scientific knowledge, the tendon system that Gemballa discovered, is a very conservative system, a trait that is common to all gnathostomata (animals with jaws), and can also be found in bony fish as well as in cartilaginous fish such as shark. Gemballa then focused on the question as to how the fish structures developed as they gradually became land-dwelling animals. Gemballa also examined the famous Latimeria, a fish specimen that is regarded as a living fossil and as a link to the quadruped land-dwelling animals.
Structure of a tendon in shortfin mako sharks. (Photo: Sven Gemballa, modified from figure in Journal of Experimental Biology Vol. 208, 2005)
Structure of a tendon in shortfin mako sharks. (Photo: Sven Gemballa, modified from figure in Journal of Experimental Biology Vol. 208, 2005)
“Latimeria still have the complete set of tendons, which are also found among lung fish, albeit in a slightly different shape. Salamanders have clearly different tendon structures. We finally concluded that the water-dwelling fish got rid of their tendon system when they made the move from water to land. The mechanical strain on the body differs considerably between quadruped land-dwelling animals and swimming fish. The reconstruction that became necessary when moving to land, also affected the tendon system of the body,” summarised Gemballa who also found slight alterations in fish that have developed a very specific way of life – for example tuna and probeagles, large pelagic predatory sharks.

Sprinter versus endurance runners

The two groups are not related to each other, but in contrast to the previously investigated lurking predators, are excellent endurance swimmers. “They differ in the same way as 100 m sprinters and marathon runners differ,” said Gemballa highlighting that this is why the tendon system of the endurance swimmers differs from that of the other fish. “Some tendons are enforced, others longer and some are even completely missing,” said Gemballa.

The comparison of different fish has given him excellent insights into the system. His next goal is to characterise the tendon structures with modern imaging systems and to clarify the biomechanical relationships. “We are hoping that techniques such as magnetic resonance tomography, MRT, will provide us with high-resolution three-dimensional pictures of the system. In this study, we are working in close cooperation with the Max Planck Institute of Biological Cybernetics which has the best MRT in the world. The first test scans will be performed shortly,” said Gemballa, who is eagerly anticipating the test runs.
The enlarged sections show what the cross section hides: Thick tendons are embedded in the muscles of the mako sharks (top section: the tendons appear white; bottom section: histological cut; tendons are dyed orange). (Photo: Sven Gemballa, modified from
The enlarged sections show what the cross section hides: Thick tendons are embedded in the muscles of the mako sharks (top section: the tendons appear white; bottom section: histological cut; tendons are stained orange). (Photo: Sven Gemballa, modified from Journal of Experimental Biology vol. 208, 2005, and Nature vol. 429, 2004)

MRT brings completely new insights into the tendon system

The MRT scans visualise soft tissue structures and are therefore well suited for differentiating connective tissue and muscular structures. These examinations offer another interesting option: “We will then be able to investigate tendons on museum sharks that must not be damaged. Since MRT provides us with complete 3D data sets, computer simulations and modelling are becoming more possible.”

In order to use the tendon system as a natural model for robot fish that are able to snake around on their own, many other investigations are still necessary. Gemballa is hoping that the close cooperation with American institutes will provide him with detailed knowledge on the transmission of force by the locomotory apparatus of fish. In addition, we still require exact data on the material properties that are being determined on isolated tendons, for example force-expansion curves. This I hope to be able to investigate in close cooperation with material scientists,” said Gemballa.

leh - 28.02.2008
© BIOPRO Baden-Württemberg GmbH
Further information:
University of Tübingen
Institute of Zoology
Prof. Dr. Sven Gemballa
Auf der Morgenstelle 28
72076 Tübingen
Tel.: +49 (0)7071 29-76947
Fax: +49 (0)7071 29-5150
E-mail: sven.gemballa@uni-tuebingen.de

Website address: https://www.biooekonomie-bw.de/en/articles/news/sharks-and-the-evolution-of-the-locomotory-apparatus