R. Van Damme

Ecomorphological analysis of trophic niche partitioning in a tropical savannah bat community

The exceptional diversity of neotropical bat communities is sustained by an intricate partitioning of available resources among the member species. Trophical specialization is considered an important evolutionary avenue towards niche partitioning in neotropical phyllostomid bats. From an ancestral insectivorous condition, phyllostomids evolved into highly specialized frugivorous, carnivorous, nectarivorous, piscivorous and even sanguivorous species. Previously, correlations between cranial morphology and trophic ecology within this group have been documented. Here, we examine the evolutionary relationships between bite force and head shape in over 20 species of bats from a single tropical savannah bat community. The results show that bite force increases exponentially with body size across all species examined. Despite the significant differences between large dietary groups using traditional analysis (i.e. non–phylogenetic) and the strong evolutionary correlations between body mass and bite force, phylogenetic analyses indicated no differences in bite performance between insectivorous, omnivorous and frugivorous bats. Comparisons of three species with highly specialized feeding habits (nectarivory, piscivory and sanguivory) with the rest of the species in the community indicate that specialization into these niches comes at the expense of bite performance and, hence, may result in a reduction of the trophic niche breadth.

Evolutionary trade-offs in locomotor capacities in lacertid lizards: are splendid sprinters clumsy climbers?

We tested the hypothesis that an evolutionary trade‐off exists between the capacity to run on level terrain and the ability to climb inclined structures in lacertid lizards. Biomechanical and physiological models of lizard locomotor performance suggest that the morphological design requirements of a ground‐dwelling vs. scansorial life style are difficult to reconcile. This conflict is thought to preclude simultaneous evolution of maximal locomotor performance on level and inclined terrain. This notion has been corroborated by comparative studies on lizard species from other groups (Anolis, Chamaeleo, Sceloporus), but is not supported by our data on 13 species from the family Lacertidae. We found no indication of a negative association between maximal sprint speed of lizards over a level racetrack (indicative of ground‐dwelling locomotor performance), on an inclined stony surface (indicative of climbing performance over rock faces) and inclined mesh surface (indicative of clambering performance among vegetation). Moreover, morphological characteristics associated with fast sprinting capacities (e.g. long hind limbs) apparently enhance, rather than hinder climbing and clambering performance. We conclude that in our sample of lacertid lizards, the evolution of fast sprinting capacity on level terrain has not inflicted major restrictions on climbing and clambering performance.

Evolutionary rigidity of thermal physiology: the case of the cool temperate lizard Lacerta vivipara

We compared the thermal dependence of sprint speed in two populations of the common lizard, Lacerta vivipara, from different altitudes. Although field body temperatures in the montane population were consistently 3-5°C below those of the lowland population, we found no parallel shift in the optimal temperatures for sprint speed. Lizards from both populations also selected similar temperatures in the laboratory. In the field, lizards from the montane population were frequently active at body temperatures that seriously impair locomotion. These observations give support to the static view of thermal physiology, which claims that thermal physiology is evolutionary stationary and resistant to directional selection.

Omnivory in lacertid lizards: adaptive evolution or constraint?

Feeding specializations such as herbivory are an often cited example of convergent and adaptive evolution. However, some groups such as lizards appear constrained in the evolution of morphological specializations associated with specialized diets. Here we examine whether the inclusion of plant matter into the diet of omnivorous lacertid lizards has resulted in morphological specializations and whether these specializations reflect biomechanical compromises as expected if omnivores are constrained by functional trade‐offs. We examined external head shape, skull shape, tooth structure, intestinal tract length and bite performance as previous studies have suggested correlations between the inclusion of plants into the diet and these traits. Our data show that omnivorous lacertid lizards possess modifications of these traits that allow them to successfully exploit plant material as a food source. Conversely, few indications of a compromise phenotype could be detected, suggesting that the evolution towards herbivory is only mildly constrained by functional trade‐offs.

Absolute versus per unit body length speed of prey as an estimator of vulnerability to predation

To study whether absolute (m/s) or relative (body lengths/s) speed should be used to compare the vulnerability of differently sized animals, we developed a simple computer simulation. Human ‘predators’ were asked to ‘catch’ (mouse-click) prey of different sizes, moving at different speeds across a computer screen. Using the simulation, a prey’s chances of escaping predation depended on its speed (faster prey were more difficult to catch than slower prey of the same body size), but also on its size (larger prey were easier to catch than smaller prey at the same speed). Catching time, the time needed to catch a prey, also depended on both prey speed and prey size. Relative prey speed (body lengths/s or body surface/s) was a better predictor of catching time than was absolute prey speed (m/s). Our experiment demonstrates that, in contrast to earlier assertions, per unit body length speed of prey may be more ‘ecologically relevant’ than absolute speed.

Fight versus flight: physiological basis for temperature-dependent behavioral shifts in lizards.

SUMMARY Previous studies have demonstrated that a behavioral shift from flight to aggressive behavior occurs at low temperatures in some lizards. Our data for the agamid lizard Trapelus pallida demonstrate how the effect of temperature on whole organism performance traits such as sprint speed (much lower performance at lower temperature) and bite force (largely independent of temperature) may explain the shift from flight to fight behavior with decreasing temperature. Moreover, our data hint at the physiological basis for this effect as isolated muscle power output, twitch and tetanus time traits, relevant to sprinting, appear to be strongly temperature-dependent muscle properties. Maximal muscle force production, on the other hand, appears largely independent of temperature. Unexpectedly, differences in the physiological properties of jaw versus limb muscle were observed that enhance the ability of the jaw muscle to generate maximal force at all temperatures tested. Thus our data show how behavioral responses may be determined by the limitations set by temperature on physiological processes.

Limb proportions in climbing and ground-dwelling geckos (Lepidosauria, Gekkonidae): a phylogenetically informed analysis

Abstract Biomechanical considerations predict that limb proportions should differ between animals with climbing and ground-dwelling lifestyles. Ground-dwellers should have relatively long, parasagittal hind limbs, with high tibia:femur ratios, and relatively short fore limbs. Climbers should have relatively short limbs, with low tibia:femur ratios, and equally long hind and fore limbs. We tested these predictions using gecko species with different locomotion habits (climbing versus ground-dwelling). We measured snout-vent length and lengths of limb segments in 29 species of geckos and analysed them using both non-phylogenetic statistics (nested analysis of variance and principal component analysis) and phylogenetic statistics (analysis of covariance). Neither approach allowed us to find any consistent relationship between habitat use and the morphometric variables. We conclude that either relative limb lengths and limb proportions in geckos have not evolved in response to the physical demands of the microhabitat, or our understanding of those demands is insufficient.

Field body temperatures and thermoregulatory behavior of the high altitude lizard, Lacerta bedriagae

Many species of lizards are known to maintain relatively high and constant body temperatures (Avery, 1982; Huey, 1982). Their abilities to do so depend largely on regulatory behaviors that alter heat exchange with the environment and on the thermal conditions within their habitats. Ectotherms living at high altitudes (and latitudes) offer unique opportunities to study thermoregulatory responses to the rather unfavorable and strongly variable thermal characteristics of these regions. High altitude lizards often exhibit lower and more variable activity body temperatures, and/or thermoregulate less precisely than conspecific or congeneric populations living at lower elevations (Brattstrom, 1965; Hertz and Nevo, 1981; Vial, 1984; Crowley, 1985). We report here results of a short-term study on field body temperatures and aspects of thermoregulatory behavior of the lizard Lacerta bedriagae. This mediumsized lizard (adult male body size = 66-84 mm, mass = 7-14 g; adult female body size = 66-80 mm, mass = 7-11 g) is endemic to the Mediterranean islands Corsica and Sardinia, where its distribution is usually retricted to altitudes >1000 m (Schneider, 1984 reviews information on the habits of this poorly known species). We hypothesized that this lizard, living in an environment characterized by low and variable ambient temperatures, would be active over a relatively wide range of body temperatures. Our main aim therefore was to examine changes in body temperature and thermoregulatory behavior in relation to diel variations in the thermal environment.

Does foraging mode mould morphology in lacertid lizards

Evolutionary changes in foraging style are often believed to require concurrent changes in a complex suite of morphological, physiological, behavioural and life‐history traits. In lizards, species from families with a predominantly sit‐and‐wait foraging style tend to be more stocky and robust, with larger heads and mouths than species belonging to actively foraging families. Here, we test whether morphology and foraging behaviour show similar patterns of association within the family Lacertidae. We also examine the association of bite force abilities with morphology and foraging behaviour. Lacertid lizards exhibit considerable interspecific variation in foraging indices, and we found some evidence for a covariation between foraging style and body shape. However, the observed relationships are not always in line with the predictions. Also, the significance of the relationships varies with the evolutionary model used. Our results challenge the idea that foraging style is evolutionarily conservative and invariably associated with particular morphologies. It appears that the flexibility of foraging mode and its morphological correlates varies among lizard taxa.

Synchronization of spring molting with the onset of mating behavior in male lizards, Lacerta vivipara

BURGER, W. L. 1950. Novel aspects of the life history of two ambystomas. J. Tenn. Acad. Sci. 25:252-257. COLLINS, J. P., AND J. R. HOLOMUZKI. 1984. Intraspecific variation in diet within and between trophic morphs in larval tiger salamanders (Ambystoma tigrinum nebulosum). Can. J. Zool. 62:168-174. DODSON, S. I., AND V. E. DODSON. 1971. The diet of Ambystoma tigrinum larvae from western Colorado. Copeia 1971:614-624. GEHLBACH, F. R. 1965. Herpetology of the Zuni Mountains region, northwestern New Mexico. Proc. U.S. Nat. Mus. 116:243-332.