Sam Van Wassenbergh

As PhD-student at the University of Antwerp starting in 2002, I studied the consequences of the drastically increased size of the jaw muscles in different species of African air-breathing catfish (Clariidae) on the mechanics of their feeding apparatus.  Working at the laboratory of Functional Morphology under the supervision of Prof. Anthony Herrel and Prof. Peter Aerts, I combined experimental work (high-speed video, X-ray video) with mathematical modelling (both analytical and computational), which led to a deeper understanding of the feeding mechanism of fish in general. In April 2006, the final chapter of my thesis, in which I presented the discovery of a novel, terrestrial feeding strategy in the catfish Channallabes apus, was published in Nature.  It became the fourth most-read article on the Nature website in 2006, and received much media attention.  I defended my thesis entitled ‘Functional consequences of jaw adductor hypertrophy on prey capture in clariid catfishes’ on 20 May 2006. More information on my PhD thesis can be found on the page ‘catfish thesis’.

Between handing in my PhD thesis and the start of my post-doc in 2006 I performed two research and training visits: (1) to perform in-vitro contractile property measurements of catfish muscles at Coventry University, Laboratory of Muscle Mechanics (Prof. Rob James), and (2) to study the functional morphology of marine fishes and perform electromyography during food capture in pipefishes at the Friday Harbor Laboratories of the University of Washington (Prof. Adam Summers, Prof. Lara Ferry, Prof. James Strother).

I then successfully applied for a post-doctoral fellowship of the Fund for Scientific Research Flanders (FWO-Vl) to work as a researcher at the University of Antwerp (2006-2012).  I conducted three main projects: firstly, I studied the biomechanics of prey capture in Syngnathidae, the group of specialized suction feeding fish which includes pipefishes and seahorses.  Experimental quantifications of muscle activity and cranial kinematics together with mathematical models allowed me to unravel the mechanics behind their extremely fast capture of prey.  Together with Prof. Peter Aerts, I was the promotor of the PhD thesis of Gert Roos, who defended his thesis ‘Functional morphological study of feeding in seahorses and pipefishes (Syngnathidae)‘ successfully in December 2010.  In January 2011, part of my work on prey-capture biomechanics of Syngnathidae, in which I present an adaptive explanation for the horse-like shape of seahorses, was published in Nature Communications.  This article also received attention of several popular media sources.

Secondly, I acquired the mathematical modelling skills of Computational Fluid Dynamics (CFD; ANSYS Fluent software) and introduced it as a tool for studying the interaction between feeding animals and their aquatic environment to the field of functional morphology of feeding in vertebrates. I still regularly collaborate with colleagues to answer functional morphological questions with a link to fluid dynamics. In a very successful collaboration, CFD was combined with force measurements in a flow tank (in collaboration with Univ. Groningen; Prof. Eize Stamhuis) to determine the hydrodynamic performance of the carapace of boxfish, a model system for the design of cars and underwater vehicles.  The latter publication received a full page of coverage in Nature in Januari 2016.

Thirdly, in 2010 I attracted a grant for a PhD fellowship funded by the University of Antwerp to continue working on the functional morphology and biomechanics of terrestrial feeding in amphibious fishes. The following years, former PhD student Krijn Michel and I studied how mudskippers, reedfishes and four-eyed fishes manage to capture and swallow their food on land.  This work featured my discovery that mudskippers use a hydrodynamic tongue during feeding on land.  Also our work on the terrestrial feeding mechanisms in the four-eyed fish was featured as a research highlight in Nature of October 2015, just around the time Krijn Michel successfully defended his thesis.

At the University of Ghent in the Research Group Evolutionary Morphology of Vertebrates lead by Prof. Dominique Adriaens, I mainly worked on three research topics.  Firstly, I was a co-investigator in a FWO-funded project ‘Integrated performance trade-off in cichlid heads: feeding versus mouth brooding’.  Together with several Bachelor students, I analyzed the drag penalty of the increase head volume of mouthbrooding cichlids.  I worked together with the SPHERE research group at the University of Antwerp (Prof. Gudrun De Boeck and Dr. Hon Jung Liew) to measure the kinematics of mouth brooding in Nile tilapias.  Secondly, I had the opportunity to perform a laboratory study on how African mole-rats use their teeth to dig tunnels. Finally, I attracted funding to purchase a high-speed camera to start an analysis of beak movement in the Java sparrow Lonchura oryzivora.  This research has allowed me to form the ideas for the main line of research for my current Tenure Track position on beak movement in songbirds.

In 2016 I attracted a project grant (Accueil de Chercheurs de Haute Niveau) from the French ANR (Agence National de Recherche) for a project entitled ‘Biomechanics of intra-oral water flow generation in fish (IOFLOW)’.  It allowed me to work in the FunEvol research group (lead by Prof. Anthony Herrel) together with Dr. Pauline Provini. We first made progress through on the development of computational fluid dynamics (CFD) models of suction feeding.  I further developed realistic, three-dimensional models by combining jaw movements with mouth-bottom depressions to create suction flows.  This work helped me to analyze the effects of the shape of the mouth on the kinematics and dynamics of suction feeding in a collaboration with Prof. Egon Heiss. Secondly, CFD was used to test one of the few hypotheses related to intra-oral flow that was present in the literature: that the shape of the posterior oropharynx is important for generating a fast and unidirectional flow through the oropharyngeal cavity.  This hypothesis was rejected, as outflow patterns and overall suction-feeding dynamics were virtually unaffected by morphological changes imposed to this region, which we reported in a paper published in Royal Society Open Science.  Thirdly, a three-dimensional, transient model of suction feeding was applied in a collaborative project on the effects of leakage due to puncture holes in the mouth cavity caused by catching fish with hooks. The results are published in The Journal of Experimental Biology in August 2018. Fourthly, I developed the protocol to use computational fluid dynamics to simulate the flows in a ram-filter feeding fish.  My geometrically simplified cross-step filtration model makes use of a thin external layer defined as a ‘Porous Medium’ in ANSYS Fluent as a model for the gill rakers. This model shows a close resemblance with published data.  A manuscript was written in collaboration with Prof. Laurie Sanderson, which has been published in Royal Society Open Science in 2023.

Dr. Provini and I managed to develop a protocol to make neutrally buoyant particles that can be used to track water flows in high-speed X-ray videos.  Designing particles to have a small size, have a small weight, and still provide enough contrast to be visible on X-ray videos, was challenging. Using these particles, three-dimensional flows of intra-oral water and food could be quantified in two species of fishes: the common carp (Cyprinus carpio) and the Nile tilapia (Oreochromis niloticus). We expect that the newly developed technique will be highly valuable for future research on aquatic flows where optical access in not convenient.  This work was published in eLife.

Since July 2019 I work full-time as a postdoc assistant serving a collaborative project (lead by Prof. Peter Aerts) between research groups of the department of Biology (FUNMORPH), the department of Physics (BIMEF and imec VISION lab), and the department of Veterinary Sciences (CoPeD lab).  I coordinate data acquisition and analysis with the 3D²YMOX system (biplanar X-ray video).  I have been involved in optimising the image quality and 3-D-kinematics analysis workflow.  I assisted in collecting data sets using this system on locomotion in piglets (PhD Falk Mielke), and rats (‘Happy Joints’ project by Prof. Ilse Jonkers and Dr. Judith Piet), as well as on the development of stereoscopic, high-speed CT-scanning techniques using our dual image intensifier system (PhDs of Joaquim Sanctorum and Van Nguyen).

I continued collaborating with colleagues from MNHN Paris. Together with Prof. Anick Abourachid and Prof. Christine Böhmer, I worked on a project the functional morphology and biomechanics of pecking in woodpeckers. This included high-speed video recording sessions in several zoos across Europe. Parts of this work were published in the Journal of Experimental Biology and in Current Biology​