Browsing by Author "Broeckhoven, Chris"
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- ItemCauses and consequences of body armour in the group-living lizard, Ouroborus cataphractus (Cordylidae)(Stellenbosch : Stellenbosch University, 2015-03) Broeckhoven, Chris; Mouton, P. le Fras N.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: Cordylidae is a family of predominantly rock-dwelling sit-and-wait foraging lizards endemic to southern Africa. The significant variation in spine length and extent of osteoderms among taxa makes the family an excellent model system for studying the evolution of body armour. Specifically, the Armadillo lizard (Ouroborus cataphractus) offers an ideal opportunity to investigate the causes and consequences of body armour. Previous studies have hypothesised that high terrestrial predation pressure, resulting from excursions to termite foraging ports away from the safety of the shelter, has led to the elaboration of body armour and a unique tail-biting behaviour. The reduction in running speed associated with heavy body armour, in turn, appears to have led to the evolution of group-living behaviour to lower the increased aerial predation risk. In this thesis, a comparative and integrative approach is used to provide more insight into the conditions under which body armour could have evolved in O. cataphractus and the consequences of body armour for life-history traits. Chapter 2 attempts to investigate how competitive and predatory pressures affect the activity patterns of O. cataphractus. Analysis of activity patterns, obtained via remote camera trapping techniques, show low levels of activity during summer in O. cataphractus, resulting from increased competition for food and high predation pressure. In contrast, a shift in activity to spring, when food availability is relatively high, appears to override the negative effects of body armour and group-living behaviour in O. cataphractus. Chapter 3 tests the hypothesis that body armour serves as protection against attacks from predators during foraging excursions away from the safety of the shelter. The relatively high skin toughness, due to the presence of thick osteoderms in the dermis, protects O. cataphractus against most terrestrial predators, while the skin toughness values for other cordylid lizards are well-below the bite forces of potential mammalian predators. The remaining chapters focus strongly on the feeding behaviour of O. cataphractus and how it is linked to body armour. Chapter 4 investigates the consequences of a reduction in running speed for the diet and tests for the presence of compensatory alternative performance capacities (i.e. increased bite force or jaw closing velocity). A comparative phylogenetic analysis shows that the possession of body armour affects the proportion of evasive prey items that can be included into the diet, thereby restricting the prey spectrum of heavily armoured taxa, such as O. cataphractus, to slow-moving prey (e.g. Coleoptera). Although the results indicate a relatively high bite force in O. cataphractus, the primary selection pressure seems to be tail-biting behaviour, rather than the consumption of hard-bodied Coleoptera (Chapter 5). Bite force, however, trades-off with jaw closing velocity in lizards. A novel lingual prehension mode, exclusive to O. cataphractus (Chapter 6) appears to have evolved in response to the force-velocity trade-off. Given the slow nature of lingual prehension, increased prey capture efficiency appears to be the main selection pressure (Chapter 7), rather than miminsing exposure to predators by reducing the time spent in the open.
- ItemEvolutionary morphology of the lizard chemosensory system(Nature Research, 2017-09-04) Baeckens, Simon; Herrel, Anthony; Broeckhoven, Chris; Vasilopoulou-Kampitsi, Menelia; Huyghe, Katleen; Goyens, Jana; Van Damme, RaoulForaging mode plays a pivotal role in traditional reconstructions of squamate evolution. Transitions between modes are said to spark concerted changes in the morphology, physiology, behaviour, and life history of lizards. With respect to their sensory systems, species that adopt a sit-and-wait strategy are thought to rely on visual cues primarily, while actively hunting species would predominantly use chemical information. The morphology of the tongue and the vomeronasal-organs is believed to mirror this dichotomy. Still, support for this idea of concerted evolution of the morphology of the lizard sensory system merely originates from studies comparing only a few, distantly related taxa that differ in many aspects of their biology besides foraging mode. Hence, we compared vomeronasal-lingual morphology among closely related lizard species (Lacertidae). Our findings show considerable interspecific variation indicating that the chemosensory system of lacertids has undergone substantial change over a short evolutionary time. Although our results imply independent evolution of tongue and vomeronasal-organ form, we find evidence for co-variation between sampler and sensor, hinting towards an ‘optimization’ for efficient chemoreception. Furthermore, our findings suggest species’ degree of investment in chemical signalling, and not foraging behaviour, as a leading factor driving the diversity in vomeronasal-lingual morphology among lacertid species.
- ItemLaboratory X-ray micro-computed tomography : a user guideline for biological samples(Oxford University Press, 2015) Du Plessis, Anton; Broeckhoven, Chris; Guelpa, Anina; Le Roux, Stephan GerhardLaboratory X-ray micro-computed tomography (micro-CT) is a fast growing method in scientific research applications that allows for non-destructive imaging of morphological structures. This paper provides an easily operated “how-to” guide for new potential users and describes the various steps required for successful planning of research projects that involve micro-CT. Background information on micro-CT is provided, followed by relevant set-up, scanning, reconstructing and visualization methods and considerations. Throughout the guide, a Jackson’s chameleon specimen, which was scanned at different settings, is used as an interactive example. The ultimate aim of this paper is make new users familiar with the concepts and applications of micro-CT, in an attempt to promote its use in future scientific studies.
- ItemSnake fangs : 3D morphological and mechanical analysis by microCT, simulation, and physical compression testing(Oxford University Press, 2018) Du Plessis, Anton; Broeckhoven, Chris; Le Roux, Stephan G.This Data Note provides data from an experimental campaign to analyse the detailed internal and external morphology and mechanical properties of venomous snake fangs. The aim of the experimental campaign was to investigate the evolutionary development of 3 fang phenotypes and investigate their mechanical behaviour. The study involved the use of load simulations to compare maximum Von Mises stress values when a load is applied to the tip of the fang. The conclusions of this study have been published elsewhere, but in this data note we extend the analysis, providing morphological comparisons including details such as curvature comparisons, thickness, etc. Physical compression results of individual fangs, though reported in the original paper, were also extended here by calculating the effective elastic modulus of the entire snake fang structure including internal cavities for the first time. This elastic modulus of the entire fang is significantly lower than the locally measured values previously reported from indentation experiments, highlighting the possibility that the elastic modulus is higher on the surface than in the rest of the material. The micro–computed tomography (microCT) data are presented both in image stacks and in the form of STL files, which simplifies the handling of the data and allows its re-use for future morphological studies. These fangs might also serve as bio-inspiration for future hypodermic needles.
- ItemSome like it hot : camera traps unravel the effects of weather conditions and predator presence on the activity levels of two lizards(Public Library of Science, 2015) Broeckhoven, Chris; Mouton, Pieter Le Fras NortierIt is generally assumed that favourable weather conditions determine the activity levels of lizards, because of their temperature-dependent behavioural performance. Inactivity, however, might have a selective advantage over activity, as it could increase survival by reducing exposure to predators. Consequently, the effects of weather conditions on the activity patterns of lizards should be strongly influenced by the presence of predators. Using remote camera traps, we test the hypothesis that predator presence and weather conditions interact to modulate daily activity levels in two sedentary cordylid lizards, Karusasaurus polyzonus and Ouroborus cataphractus. While both species are closely related and have a fully overlapping distribution, the former is a fast-moving lightly armoured lizard, whereas the latter is a slow-moving heavily armoured lizard. The significant interspecific difference in antipredator morphology and consequently differential vulnerability to aerial and terrestrial predators, allowed us to unravel the effects of predation risk and weather conditions on activity levels. Our results demonstrate that K. polyzonus is predominantly active during summer, when ambient temperatures are favourable enough to permit activity. In contrast, a peak in activity during spring was observed in O. cataphractus, with individuals being inactive during most of summer. While favourable weather conditions had a strong effect on the activity levels of K. polyzonus, no such relationship was present in O. cataphractus. Contrary to our hypothesis, the presence of terrestrial predators does not seem to affect daily activity levels or alter the influence of weather conditions on activity levels. We conclude that inactivity in O. cataphractus appears to be related to seasonal differences in vulnerability to predators, rather than the presence of predators, and highlight the importance of additional selective pressures, such as food abundance, in determining the species’ activity levels.