Papers by Raoul Van Damme
Animal body armour is often considered an adaptation that protects prey against predatory attacks... more Animal body armour is often considered an adaptation that protects prey against predatory attacks, yet comparative studies that link the diversification of these allegedly protective coverings to differential predation risk or pressure are scarce. Here, we examine the evolution of body armour, including spines and osteoderms, in Cordylinae, a radiation of southern African lizards. Using phylogenetic comparative methods, we attempt to identify the ecological and environmental correlates of body armour that may hint at the selective pressures responsible for defensive trait diversification. Our results show that species inhabiting arid environments are more likely to possess elaborated body armour, specifically osteoderms. We did not find any effect of estimated predation pressure or risk on the degree of body armour. These findings suggest that body armour might not necessarily evolve in response to direct interactions with predators, but rather as a result of increased habitat-mediated predation risk. Furthermore, we discuss the possibility that osteoderms might have been shaped by factors unrelated to predation.
Animal Cognition, Jan 17, 2022
Animals exhibit considerable and consistent among-individual variation in cognitive abilities, ev... more Animals exhibit considerable and consistent among-individual variation in cognitive abilities, even within a population. Recent studies have attempted to address this variation using insights from the field of animal personality. Generally, it is predicted that animals with "faster" personalities (bolder, explorative, neophilic) should exhibit faster but less flexible learning. However, the empirical evidence for a link between cognitive style and personality is mixed. One possible reason for such conflicting results may be that personality-cognition covariance changes along ecological conditions, a hypothesis that has rarely been investigated so far. In this study, we tested the effect of habitat complexity on multiple aspects of animal personality and cognition, and how this influenced their relationship, in five populations of the Aegean wall lizard (Podarcis erhardii). Overall, lizards from both habitat types did not differ in average levels of personality or cognition, with the exception that lizards from more complex habitats performed better on a spatial learning task. Nevertheless, we found an intricate interplay between ecology, cognition and personality, as behavioral associations were often habitat-but also year-dependent. In general, behavioral covariance was either independent of habitat, or found exclusively in the simple, open environments. Our results highlight that valuable insights may be gained by taking ecological variation into account while studying the link between personality and cognition.
Functional Ecology, Apr 1, 2003
1. Microhabitat use and antipredator behaviour (i.e. behavioural response to a bird model and ref... more 1. Microhabitat use and antipredator behaviour (i.e. behavioural response to a bird model and refuge microhabitat) was measured in an experimental set-up for 11 lacertid lizard species. Additionally, locomotor performance (sprint speed, climbing and clambering speed, manoeuvrability and endurance) of the same species was quantified. 2. The results showed considerable interspecific variation in microhabitat use, behavioural response and choice of refuge microhabitat. Part of that variation could be linked to differences in locomotor capacity. 3. Species that frequently made use of open microhabitats tended to be fast sprinters, but had limited endurance. The behavioural data suggest these species will not start running before the predator is close at hand, and thus having high sprint capacities might be more beneficial than great endurance. 4. Species that spent most of their time on vertical elements appeared to be fast climbers. As such microhabitats tend to be quite exposed, lizards living there are conspicuous to predators and being able to escape fast seems relevant. 5. Contrary to our expectations, species mostly observed in the vegetated microhabitats did not excel in clambering capacity or manoeuvrability. Possibly, dense vegetation constitutes a safe harbour and species may no longer be under selection for locomotor speed. 6. Behavioural response when confronted with an aerial predator was context-dependent in most species: most lizards fled more when in open or vertical microhabitats than when in densely vegetated ones. Moreover, when fleeing most species sought refuge in the vegetation. These findings support our idea that vegetated patches may constitute a safe harbour for lacertids.
Journal of Zoology, Nov 1, 2002
We tested the hypothesis that the number of presacral vertebrae in lacertid lizards has evolved t... more We tested the hypothesis that the number of presacral vertebrae in lacertid lizards has evolved to meet requirements set by the structural habitat. The idea was that lizards from cluttered habitats (densely vegetated areas, stony walls and hills, rocks) would be aided by a ¯exible backbone with many vertebrae, ensuring manoeuvrability, whereas lizards from open habitats would require stiffer vertebrate columns, with relatively few vertebrae, favouring speed and acceleration capacity. In contrast to earlier ®ndings in ®shes and snakes, evolution of vertebral number and body size was uncorrelated in lacertid lizards. Body size also did not differ between structural habitat types (open areas, densely vegetated areas, vertical elements). Traditional analysis of variance suggests strong differences in vertebral counts between species from open areas and cluttered areas, the latter having higher numbers of presacral vertebrae. When adequate phylogenetic analyses are used, differences remain signi®cant although the level of signi®cance is considerably lower. Tests of the mechanistic relationships between vertebral number, bending ability, and manoeuvrability, and assessment of the relative importance of manoeuvrability and speed in habitats with varying degrees of impediment are needed to reveal the evolutionary path that has led to the differences in vertebral number.
Philosophical Transactions of the Royal Society B, Aug 6, 2003
This paper illustrates how simple mechanical models based on morphological, ethological, ecologic... more This paper illustrates how simple mechanical models based on morphological, ethological, ecological and phylogenetic data can add to discussions in evolutionary biology. Bipedal locomotion has evolved on numerous occasions in lizards. Traits that appear repeatedly in independent evolutionary lines are often considered adaptive, but the exact advantages of bipedal locomotion in lizards remain debated. Earlier claims that bipedalism would increase maximal running speed or would be energetically advantageous have been questioned. Here, we use 'whole body' mechanical modelling to provide an alternative solution to the riddle. The starting point is the intermittent running style combined with the need for a high manoeuvrability characterizing many small lizard species. Manoeuvrability benefits from a caudal shift of the centre of mass of the body (body-COM), because forces to change the heading and to align the body to this new heading do not conflict with each other. The caudally situated body-COM, however, might result in a lift of the front part of the body when accelerating (intermittent style), thus resulting in bipedal running bouts. Based on a momentum-impulse approach the effect of acceleration is quantified for a mechanical model, a virtual lizard (three segments) based on the morphometrics of Acanthodactylus erythrurus (a small lacertid lizard). Biologically relevant input (dimensions, inertial properties, step cycle information, etc.) results in an important lift of the front part of the body and observable distances passively covered bipedally as a consequence of the acceleration. In this way, no functional explanation of the phenomenon of lizard bipedalism is required and bipedalism can probably be considered non-adaptive in many cases. This does not exclude, however, some species that may have turned this consequence to their benefit. For instance, instantaneous manipulation of the position of the centre of the body-COM allows stable, persisting bipedal running. Once this was achieved, the bipedal spandrel could be exploited further.
Functional Ecology, Jun 1, 2000
Morphological features (i.e. snout-vent length, SVL, mass and limb parameters), locomotor perform... more Morphological features (i.e. snout-vent length, SVL, mass and limb parameters), locomotor performance (sprint speed, climbing speed, manoeuvrability and endurance) and microhabitat use were measured in three lacertid lizard species. Additionally, microhabitat preference was tested in the laboratory with species kept apart and in combination with each other to assess mutual interference. 2. It was predicted that each species possesses morphological adaptations that allow it to excel in those performance measures relevant in its particular microhabitat. 3. The three species differed in microhabitat use. Lacerta bedriagae was mostly seen on boulders, while Podarcis sicula occurred among vegetation. Podarcis tiliguerta seemed more general in its microhabitat use. The results from the microhabitat preference in the laboratory corresponded well to these field observations. 4. Besides differing in SVL, the three species differed in limb length and diameter, and body mass (all relative to SVL). L. bedriagae has long forelimbs, short hindlimbs and a high body mass, while P. sicula has short forelimbs, long hindlimbs and a low body mass. P. tiliguerta is morphologically intermediate. 5. The differences found in morphology translated partially into performance differences. Only climbing speed and endurance differed among species. L. bedriagae excelled in both cases. Considering its microhabitat use, this seemed adaptive. 6. Unexpectedly, the interference experiments suggested that L. bedriagae is the least competitive of the three species.
Oikos, Aug 1, 2007
We investigated the possible role of variation in predation pressure in the phenotypic divergence... more We investigated the possible role of variation in predation pressure in the phenotypic divergence of two island populations of the Italian wall lizard, Podarcis sicula . In 1971, ten adult specimens from the island of Pod Kopis ˇte (Adriatic Sea, Croatia) were transported to the island of Pod Mrc ˇaru, 3.5 km east, where they founded a new population. Although the two islands resemble each other in general physiognomy (size, elevation, microclimate) and in the absence of terrestrial predators, lizards from the newly established population are now on average larger and have shorter hind limbs. They also exhibit lower maximal sprint speed as measured on a racetrack, and fatigue faster when chased in a torus track. In the field, lizards from the original population of Pod Kopis ˇte respond to a simulated predatory attack by fleeing at larger approach distances and by running further from the predator than lizards from Pod Mrc ˇaru. These changes in morphology, behaviour and performance may result from the relaxed predation intensity on the latter island. Our analysis of the structural features of the microhabitats suggests that the vegetation on Pod Mrc ˇaru offers more protection to lizards. Also, plasticine models of lizards, laid out on the islands, less often exhibited signs of being attacked by birds on Pod Mrc ˇaru than on Pod Kopis ˇte. Our findings provide an example of how changes in (possibly a single) environmental factor may simultaneously produce responses in behaviour, morphology and whole-animal physiology, and this on a surprisingly small spatial and temporal scale.
Research Square (Research Square), Oct 18, 2022
Women's representation in science is increasing steadily, with some elds closing gender parity in... more Women's representation in science is increasing steadily, with some elds closing gender parity in terms of participation and scienti c output. Animal Cognition appears to fall into that category. However, a careful analysis of gender author balance in 600 animal cognition papers revealed some remaining disparities. Despite that female animal cognition scientists dominate rst authorship positions, receive equal citations, and publish in equally high quality journals, they are still severely under-represented in positions of seniority. In addition, disparities remain at the group level, where all-female author teams are not only the minority in our dataset, but also seem to receive disproportionally less citations than all-male author teams, regardless the quality of the publications. We also found that female animal cognition scientists focus on different taxa, and tend to include study animals of both sexes more often than male scientists. Our study suggests that despite the meaningful contribution of female scientists to the eld, Animal Cognition continues to be marred by gender biases.
Amphibia-reptilia, 2009
The millions of conserved biological specimens that are stored upon the shelves of Natural Histor... more The millions of conserved biological specimens that are stored upon the shelves of Natural History Museums across the world constitute a capital of biological information that is becoming increasingly accessible to students of various disciplines. Most students have taken measures of body size and shape of preserved museum specimens to test various elements of ecological and evolutionary theory. One possible hazard of using morphological measurements of museum specimens is that fixation and preservation may deform bodies or body parts, but most researchers implicitely assume that the magnitude of conservation-induced distortions are insufficient to jeopardize their analyses. However, no study to our knowledge has clearly quantified those possible distortions. In this study, we have measured 17 morphological variables on a set of 65 green iguanas (Iguana iguana), starting shortly after their death and then repeatedly over a two month period, a period during which they were fixated and preserved. Our aims were (1) to quantify and compare the deformation in different morphometrics frequently used in evolutionary studies; (2) to determine the amount of temporal variation that can be attributed to reader variability; and (3) to build conversion equations that should improve the reliability of morphological comparisons of life and conserved specimens. Conserved lizards revealed major reduction in snout vent length and body weight. Changes in other measured traits are more subtle, but persistent. These facts disturb analyses when using relative measurements, especially when comparing (often small) intraspecific differences or even morphological differences within populations in a temporal frame. We urge caution in using museum specimens as direct proxies for living organisms in ecological and taxonomic studies.
Biological Journal of The Linnean Society, Apr 9, 2019
Shape variation in the vestibular system is often linked to microhabitat structure and locomotor ... more Shape variation in the vestibular system is often linked to microhabitat structure and locomotor performance. Highly circular and orthogonal semicircular canal pairs are linked to higher motion sensitivity. Here, we use 3D geometric morphometrics to investigate shape variation in the vestibular system within lacertid lizards and its relationship to balance control. We found that lacertids living in complex microhabitats possess narrow but longer vestibular systems, an S-shaped anterior canal, a straightened lateral canal and a short common crus. However, lacertids specialized for simple microhabitats (open areas) possess wider but shorter vestibular systems, more circular anterior and lateral canals, and a longer common crus. Contrary to our expectations, species living in simple microhabitats possess more anatomical adaptations that enhance the sensitivity of their vestibular system. This suggests that species inhabiting open areas may benefit from increased sensitivity given that they are potentially more visibile to predators and have lower shelter availability. Finally, the wider shape of the vestibular system of the open area species may be linked to a wider and potentially flattened skull, which may be related to sand-diving or prey hardness.
Functional Ecology, Apr 1, 2005
1. We investigated the morphological responses of larval Rana lessonae to the presence of two pre... more 1. We investigated the morphological responses of larval Rana lessonae to the presence of two predators with substantially different prey-detection and capture techniques; larval dragonflies (Aeshna cyanea) and the Pumpkinseed Sunfish (Lepomis gibossus). 2. We also examined the functional implications of any predator-induced morphological variation on their swimming ability by assessing performance during the initial stages of a startle response. 3. We found the morphological responses of larval R. lessonae were dependent on the specific predator present. Tadpoles raised in the presence of dragonfly larvae preying upon conspecific tadpoles developed total tail heights 5•4% deeper and tail muscles 4•7% shallower than tadpoles raised in a non-predator environment, while tadpoles raised with sunfish possessed tails 2% shallower and tail muscles 2•5% higher than non-predator-exposed tadpoles. 4. Predator-induced morphological variation also significantly influenced swimming performance. Tadpoles raised with sunfish possessed swimming speeds 9•5 and 14•6% higher than non-and dragonfly predator groups, respectively. 5. Thus, the expression of these alternative predator-morphs leads to a functional trade-off in performance between the different environments.
Ethology, 2020
Lacertid lizards are known to have keen chemical senses: (a) the olfactory system with the sensor... more Lacertid lizards are known to have keen chemical senses: (a) the olfactory system with the sensory epithelium situated in the nose and (b) the vomerolfactory system in which scent molecules are transported via the tongue to the Jacobson's organ in the roof of
Amphibia-reptilia, 2013
In many animals, aspects of colouration are hypothesized to convey information on the body condit... more In many animals, aspects of colouration are hypothesized to convey information on the body condition or quality of individuals. This idea has been tested primarily for the carotenoid-based component of body colouration. The significance of other pigments in this context has received far less attention. In the common lizard, Zootoca vivipara, the degree of black patterning on the ventrum and throats is sexually dimorphic and varies considerably among individuals. In this study, we examine whether this melanin-based component of body colouration may reflect individual differences in quality (SVL, condition, immune response). We find that males (but not females) with a higher degree of ventral patterning mount a stronger phytohemagglutinin-induced immune response. The amount of black patterning does not correlate with body size, body condition, aspects of dorsal colouration or parasite load. We conclude that in male Zootoca vivipara, melanin-based ventral colouration may signal an aspect of immune capacity to sexual rivals or potential partners.
Physiological and Biochemical Zoology, 2017
Most organisms are limited in the amount and type of resources they are able to extract from the ... more Most organisms are limited in the amount and type of resources they are able to extract from the environment. The juvenile environment is particularly important in this regard, as conditions over ontogeny can influence the adult phenotype. Whole-organism performance traits, such as locomotion, are susceptible to such environmental effects, yet the specific biotic and abiotic factors driving performance plasticity have received little attention. We tested whether speckled wood Pararge aegeria L. butterflies reared under conditions of water stress exhibited poorer flight morphology and performance than control individuals. Despite large differences in mortality between treatments, we found no effects of water stress treatment on takeoff performance and only minor treatment effects on flight morphology. However, butterflies reared on water-stressed diets exhibited both significantly greater mortality and longer development times than did control individuals. Pararge aegeria larvae may compensate for this stress by prolonging development, resulting in similar realized performance capacities at least in takeoff performance in surviving adult butterflies; other measures of flight performance remain to be considered. Alternatively, the adult phenotype may be insulated from environmental effects at the larval stage in these insects.
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Papers by Raoul Van Damme