Research Anthony Herrel

Abstract

Darwin's finches (Geospizinae) have become a model system for the study of adaptive radiaton. From a single ancestor, thirteen species of Darwin's finches have radiated on the Galápagos Islands, have specialized on different food resources and differ in beak form. Despite the importance of beak size and shape in Darwin's finches ecology, the mechanical link between these aspects of beak morphology and the ability of a bird to crack seeds of different size and hardness remains unknown. Those biological theories can only be validated or refuted by an interdisciplinary approach, based on physical computational modelling. International cooperation supplies us of rare specimens from different species. The in-vivo biting force and place, CT images and histological cuts from different (protected) Darwin's finches and the physiological cuts from which the maximum muscle force could be calculated are important to make a realistic model. The research consists of two parts. First we have the computer modelling part (Finite elements simulations with FEBio), and second, an experimental part for judging the necessary boundary conditions for the simulation, hence validating and optimizing the FE model. Converning the validation, we will use the more common java finches (Padda oryzivora).

Researcher(s)

• Promoter: Dirckx Joris
• Co-promoter: Aerts Peter
• Co-promoter: Herrel Anthony
• Fellow: Soons Joris

Research team(s)

• Biophysics and Biomedical Physics

Project type(s)

• Research Project

Abstract

Darwin's finches (Geospizinae) have become a model system for the study of adaptive radiaton. From a single ancestor, thirteen species of Darwin's finches have radiated on the Galápagos Islands, have specialized on different food resources and differ in beak form. Despite the importance of beak size and shape in Darwin's finches ecology, the mechanical link between these aspects of beak morphology and the ability of a bird to crack seeds of different size and hardness remains unknown. Those biological theories can only be validated or refuted by an interdisciplinary approach, based on physical computational modelling. International cooperation supplies us of rare specimens from different species. The in-vivo biting force and place, CT images and histological cuts from different (protected) Darwin's finches and the physiological cuts from which the maximum muscle force could be calculated are important to make a realistic model. The research consists of two parts. First we have the computer modelling part (Finite elements simulations with FEBio), and second, an experimental part for judging the necessary boundary conditions for the simulation, hence validating and optimizing the FE model. Converning the validation, we will use the more common java finches (Padda oryzivora).

Researcher(s)

• Promoter: Dirckx Joris
• Co-promoter: Aerts Peter
• Co-promoter: Herrel Anthony
• Fellow: Soons Joris

Research team(s)

• Biophysics and Biomedical Physics

Project type(s)

• Research Project

Abstract

Researcher(s)

• Promoter: Van Damme Raoul
• Co-promoter: Herrel Anthony
• Fellow: Cools Annemie

Research team(s)

• Functional Morphology

Project type(s)

• Research Project

Abstract

The overall goal of this project is to investigate to what degree the extreme morphological specialisation of the feeding system in syngnathids has constrained its functional capacity, and to explore whether this can explain the reduced ecological resilience of syngnathids in the face of changing ecological settings (i.e. changes in trophic resources).

Researcher(s)

• Promoter: Herrel Anthony
• Co-promoter: Aerts Peter

Research team(s)

• Functional Morphology

Project type(s)

• Research Project

Abstract

Measurements of shape and material parameters are measured and incorporated in a finite element model for investigation of the functional characteristics of muscular-sceletal cranial structures of Darwin finches, to gain understanding of phenotypic variation and ecological diversity.

Researcher(s)

• Promoter: Dirckx Joris
• Co-promoter: Aerts Peter
• Co-promoter: Herrel Anthony

Research team(s)

• Biophysics and Biomedical Physics

Project type(s)

• Research Project

Abstract

The structure of the mammalian skull is often used as a textbook example of optimal design. However, as more experimental data became available the design appeared less optimal than suggested by theoretical approaches. Surprisingly little is, however, known about design criteria of the skull in other vertebrate groups. The skull in lizards, for example, is much more variable and appears, at first sight, well designed to withstand loads during prey processing. To gain insights into the function and design of any mechanical structure the loads and stresses applied to the structure must be known. For biological materials such as bone, this can be done using strain gauges that measure local deformations at the surface of a bone. Given an appropriate calibration, these can be used to gain insights into the loading regime of the cranial bones. In the current project this approach will be used to test optimality criteria in the evolution of the lizard skull.

Researcher(s)

• Promoter: Herrel Anthony

Research team(s)

• Functional Morphology

Project type(s)

• Research Project

Abstract

From the very start (e.g. Darwin 1845, Wallace 1859), the faunas of island groups have played a special role in the growth of our understanding of evolutionary changes and speciation - and they continue to do so (e.g. Losos et al. 1997, 2004). Islands in archipelagos constitute repeated, discrete and relatively simple entities and therefore function as 'natura/laboratories' that can be used to test general theories (Whittaker 1998). The (often prominent) differences in phenotype (morphology, behaviour, ecology, life history) among island populations or between island and mainland populations are almost invariably attributed to genetic divergence, but it is often unclear which evolutionary processes (founder effect, genetic drift, natural selection, introgression, ...) induce these differences (Barton 1989, Clarke & Grant 1996). The alternative explanation, that the differences arise from phenotypic plasticity, is often not considered (Losos et al. 2000). In this project, we intend to take advantage of an exceptional opportunity to unravel the causes of fenotypic divergence among (island) populations.

Researcher(s)

• Promoter: Van Damme Raoul
• Co-promoter: Backeljau Thierry
• Co-promoter: Herrel Anthony
• Co-promoter: Vanhooydonck Bieke

Research team(s)

• Functional Morphology

Project type(s)

• Research Project

Abstract

Jumping in frogs is a peculiar mode of locomotion, which together with the derived anatomy of the pelvic girdle, makes it unique among vertebrates. Frog hindlimbs are much more developed than the anterior ones, the tail is vestigial and the ilia are elongated posteriorly so that the pelvic joint is located behind the sacrum. There are two major hypotheses attempting to explain origin of the saltatory locomotion in frogs and the unique derived anatomy of the locomotor apparatus. The first is largely based on the fossil record, and argues that frogs evolved from larval (i.e., water dwelling) temnospondyl amphibians (i.e. that frogs are derived from aquatic ancestors). The second hypothesis emphasizes a strictly terrestrial origin of frogs, and uses as the predominant argument against the first hypothesis that there would be no reason to modify undulatory swimming movements and to reduce the tail of the ancestral temnospondyl larvae if the transition from the pre-anuran to anuran stages would occur exclusively in water. We are convinced that this controversy cannot be solved unless we understand the functioning of the anuran pelvic girdle and its musculature during locomotion. We therefore propose to investigate terrestrial and aquatic locomotion and the anatomy of the pelvic girdle in frogs that have specialized into different locomotor modes (i.e. swimmers, jumpers, diggers and crawlers). Additionally we want to study the functioning of the locomotor system during the ontogenetic transition from water to land. This kind of data should allow for a better interpretation of the fossil evidence and allow us to determine the evolutionary origin of this unique locomotor mode.

Researcher(s)

• Promoter: Aerts Peter
• Co-promoter: Herrel Anthony
• Co-promoter: Van Damme Raoul

Research team(s)

• Functional Morphology

Project type(s)

• Research Project

Abstract

Previous research into the effects of size on the functioning of the feeding system in the African catfish suggest a discordance between the scaling of morphology and the actual movements. The goal of the present project is to investigate this apparent paradox by studying the scaling of the muscle physiology. This will be done in collaboration with Dr. R. James (Coventry University), an expert in the field of vertebrate muscle physiology.

Researcher(s)

• Promoter: Herrel Anthony

Research team(s)

• Functional Morphology

Project type(s)

• Research Project

Abstract

The evolution of a terrestrial feeding mode and the origin of the amniote skull structure have undoubtably been key phenomena in the evolution of vertebrates. Althoug there is a substantial body of work, dealing with the craniocervical structure and feeding systems in mammals and birds, relatively little is known about these systems in lower tetrapods. Still, the study of these basal groups is essential to gain insights in the evolutionary processes that shaped the feeding system. Within the scope of this post-doc two topics are proposed for further study. First, the neuromotor basis of feeding in lizards will be examined. Here, emphasis will be placed on investigations into the presumed stereotypy of feeding motor patterns. Additionally we will investigate the presence, prevalence and importance of feedback systems in the evolution of lizard feeding systems. The second question I would like to address within the scope of this post-doc concerns the ecomorphological relations of the feeding apparatus in lizards. Using a broad, comparative approach within a strict phylogenetic context, we will investigate the importance of several performance parameters of the feeding system in lizards. This should allow us to identify those elements which played a critical role in the evolutionary diversification of the feeding system in lizards. The techniques and statistical methods that will be used to analyse these types of data (which will be learned in the lab. of Dr. D. Irschick, Tulane University - New Orleans), will eventually also be used to analyse the evolution of neuromotor control of the feeding system in lizards.

Researcher(s)

• Promoter: Aerts Peter
• Fellow: Herrel Anthony

Research team(s)

• Functional Morphology

Project type(s)

• Research Project

Abstract

Whereas traditionally evolutionary biologists belivied in the `almighty' power of evolution by natural selection, more recently the emphasis has changed to the study of procecces that slow down or prevent evolutionary cahnge. Evolutionary trade-offs, for example, occur when different functional tasks put conflicting demands on a functional system. Caribbean Anolis lizards have become a textbook example of adaptive radiation in the past decennia. On islands in the Caribbean, Anolis lizards have independently radiated into forms with similar ecological and morphological characteristics, termed ecomorphs. Besides the obvious differences in leg dimensions large differences in head shape exist among ecomorphs. Although researchers have speculated about potential functional relevance of these differences in head shape, very little is known about the functional implications of differences in head shape in these lizards. The variation among ecomorphs appears to be situated on a gradient from robust and stocky to slender and pointy. This variation thus appears to be correlated with the existence of a functional trade-off between bite force and jaw closing speed. Indeed, biomechanical theory predicts that animals with long jaws will be faster and will be better at catching evasive prey. Animals with short, stocky heads, on the other hand, ae predicted to be better biters. To investigate the functional trade-off predicted to lie at the basis of the observed varaiation in head shape among Anolis ecomorphs we have to be able to accurately quantify jaw closing speed. To do so, we need high-speed recordings of animals capturing prey in nature. As prey capture in lizards is fast, as we cannot get to close to the animals in the field (in order not to disturb them) and as we cannot zoom in to much because of the unpredictable nature of natural behaviour, we need a system that can film at high speed and at high resolution. Recently, an affordable version of such a system has become commercially available. Additionally, the system can be integrated in a portable computer which makes the setup field portable. The grant obtained for the current project will be used to purchase such a system and will be used to investigate the presence of evolutionary trade-offs in the feeding system of Anolis lizards.

Researcher(s)

• Promoter: Herrel Anthony

Research team(s)

• Functional Morphology

Project type(s)

• Research Project

Abstract

Because water is 800 times denser and 50 times more viscous than air, it puts very strong demands on the feeding system of vertebrates. An aquatic predator that approaches a prey will generate bow waves that can either push the prey further away or along a predator's jaws. To avoid or compensate for those bow waves, we find two systems among aquatic vertebrates: filter feeding and suction feeding. However, aquatic snakes seem not able to perform filter- or suction feeding because of their very specialised head morphology (for the consumption of large prey). Still more than 300 snake species feed in an aquatic environment on a variety of prey and with a range of different feeding morphologies and behaviours. High-speed video recordings and Particle Image Velocimetry on the strikes of Natrix maura and N. tesselata with altered predator and prey characteristics will allow us to gain insight in how the process of aquatic feeding in snakes precisely works and through which factors this process is influenced. This information will be completed with measurements on a physic snake model to look at the effects of a broader range of prey- and predator characteristics (functional morphology part). Finally we will try to consider if it is possible with the obtained insights, to link the large variation in head morphology and feeding behaviour among aquatic snakes, to the variety of different prey they eat (ecomorphological part). Data on the head morphology of aquatic snake species will be obtained by measuring museum species; data on the feeding behaviour and diet of aquatic snake species will be collected from literature.

Researcher(s)

• Promoter: Aerts Peter
• Co-promoter: Herrel Anthony
• Fellow: Bilcke Joke

Research team(s)

• Functional Morphology

Project type(s)

• Research Project

Abstract

That size has a major effect on the function of organisms has long been known. Yet, few studies have examined the effects of size on the jaw movements of fish during prey capture. Knowing how size effects movements is essential in comparative studies where often animals of different sizes are compared. As feeding movements in fish are complex and rapid phenomena, these will be examined using high-speed cineradiographic techniques.

Researcher(s)

• Promoter: Herrel Anthony

Research team(s)

• Functional Morphology

Project type(s)

• Research Project

Abstract

Motion analysis is one of the important tools in the functional morphological study of the evolution of musculo-skeletal systems as it, in combination with other functional data (such as muscle activation patterns, force measurements, etc...), allows the determination of the functional demands on the system in its ecolocical context. Whenever movement patterns can be determined externally, the analyses thereof involve the digitisation of conventional video sources (at low or high speeds, depending on the application under study ). However, often essential movements of the musculo-skeletal system of interest cannot be observed externally as the structures are covered by skin, fur or feathers (eg. movements of the pectoral and pelvic girdles in running animals, movements of the tongue and hyoid apparatus during feeding, air flow through the lungs during breathing,...). In all such cases cineradiography is "the tool of choice" to visualise these movements. In cineradiographic analysis the object under study is "illuminated" by a X-ray generator emitting pulsed or continuous X-rays. The emitted radiation is partially absorbed (depending on the density and absorption capacity of the tissue), and is received by an image intensifier and turned into a visual image. In the past, this image was generated by a phosphorising screen that, in turn, was filmed by means of a regular film camera. By synchronising the pulse frequency emitted by the generator and the shutter of the camera, movements could be recorded accurately. However, the recording speed was inherently limited by the fairly long decay time of the phosphorising screen. As for most technical applications, the recent advances in digital technology have had an enormous influence on cineradiographic techniques which has resulted in direct, digital video imaging of the cineradiographic images. This has a number of important advantages over the older technique.

Researcher(s)

• Promoter: Aerts Peter
• Co-promoter: De Vree Frits
• Co-promoter: Herrel Anthony
• Co-promoter: Van Damme Raoul

Research team(s)

• Functional Morphology

Project type(s)

• Research Project

Abstract

The evolution of a terrestrial feeding mode and the origin of the amniote skull structure have undoubtably been key phenomena in the evolution of vertebrates. Althoug there is a substantial body of work, dealing with the craniocervical structure and feeding systems in mammals and birds, relatively little is known about these systems in lower tetrapods. Still, the study of these basal groups is essential to gain insights in the evolutionary processes that shaped the feeding system. Within the scope of this post-doc two topics are proposed for further study. First, the neuromotor basis of feeding in lizards will be examined. Here, emphasis will be placed on investigations into the presumed stereotypy of feeding motor patterns. Additionally we will investigate the presence, prevalence and importance of feedback systems in the evolution of lizard feeding systems. The second question I would like to address within the scope of this post-doc concerns the ecomorphological relations of the feeding apparatus in lizards. Using a broad, comparative approach within a strict phylogenetic context, we will investigate the importance of several performance parameters of the feeding system in lizards. This should allow us to identify those elements which played a critical role in the evolutionary diversification of the feeding system in lizards. The techniques and statistical methods that will be used to analyse these types of data (which will be learned in the lab. of Dr. D. Irschick, Tulane University - New Orleans), will eventually also be used to analyse the evolution of neuromotor control of the feeding system in lizards.

Researcher(s)

• Promoter: Aerts Peter
• Promoter: De Vree Frits
• Fellow: Herrel Anthony

Research team(s)

• Functional Morphology

Project type(s)

• Research Project

Abstract

The requested funds will allow the purchase of a TEAC RD 145T digital DAT recorder and 4 Gould amplifiers. 8y using such a set-up, a direct, digital and simultaneous recording of muscle activity patterns on at least sixteen channels during prolonged time periods will be possible. As this makes the exteremely time-consuming digitisation of multiple analog signals superfluous, these techniques will enable us to efficiently sample the large number of taxa required for current comparative analyses. Ultimately we foresee novel insights into the evolution of the motor control of complex integrated systems, and associated constraints, to be gained by this innovating approach.

Researcher(s)

• Promoter: Herrel Anthony

Research team(s)

• Functional Morphology

Project type(s)

• Research Project

Abstract

The feeding apparatus is one of the exemplary cases of integrated multifunctional networks. The study of such systems within a broad phylogenetic scope can learn us more about the evolutionary constraints operating on complex integrated systems. Especially the neural control and steering of such systems seems to be conservative in evolutionary terms. However, only by comparing the feeding mechanics and systems of primitive and more complex species and/or groups, more general insights can be obtained. In this context lizards can play a crucial role as primitive amniotes, and the study of the functioning of lizard feeding apparatus can thus provide new insights into the origin and evolution of the complex feeding systems as observed.

Researcher(s)

• Promoter: De Vree Frits
• Fellow: Herrel Anthony

Research team(s)

Project type(s)

• Research Project

Abstract

The feeding apparatus in Agamids will be studied by means of quantitive EMG, high-speed and X-ray recordings. The inter and intra specific differences present will be evaluated, focusing on the differences between insectivorous and herbivorous species.

Researcher(s)

• Promoter: De Vree Frits
• Fellow: Herrel Anthony

Research team(s)

Project type(s)

• Research Project

Abstract

The feeding apparatus in Agamids will be studied by means of quantitive EMG, high-speed and X-ray recordings. The inter and intra specific differences present will be evaluated, focusing on the differences between insectivorous and herbivorous species.

Researcher(s)

• Promoter: De Vree Frits
• Fellow: Herrel Anthony

Research team(s)

Project type(s)

• Research Project

Abstract

The feeding apparatus in Agamids will be studied by means of quantitive EMG, high-speed and X-ray recordings. The inter and intra specific differences present will be evaluated, focusing on the differences between insectivorous and herbivorous species.

Researcher(s)

• Promoter: De Vree Frits
• Fellow: Herrel Anthony

Research team(s)

Project type(s)

• Research Project