Raoul Van Damme

Rapid large-scale evolutionary divergence in morphology and performance associated with exploitation of a different dietary resource

Although rapid adaptive changes in morphology on ecological time scales are now well documented in natural populations, the effects of such changes on whole-organism performance capacity and the consequences on ecological dynamics at the population level are often unclear. Here we show how lizards have rapidly evolved differences in head morphology, bite strength, and digestive tract structure after experimental introduction into a novel environment. Despite the short time scale (≈36 years) since this introduction, these changes in morphology and performance parallel those typically documented among species and even families of lizards in both the type and extent of their specialization. Moreover, these changes have occurred side-by-side with dramatic changes in population density and social structure, providing a compelling example of how the invasion of a novel habitat can evolutionarily drive multiple aspects of the phenotype.

SPEED AND STAMINA TRADE-OFF IN LACERTID LIZARDS

Abstract Morphological and physiological considerations suggest that sprinting ability and endurance capacity put conflicting demands on the design of an animals locomotor apparatus and therefore cannot be maximized simultaneously. To test this hypothesis, we correlated size-corrected maximal sprint speed and stamina of 12 species of lacertid lizards. Phylogenetically independent contrasts of sprint speed and stamina showed a significant negative relationship, giving support to the idea of an evolutionary trade-off between the two performance measures. To test the hypothesis that the trade-off is mediated by a conflict in morphological requirements, we correlated both performance traits with snout-vent length, size-corrected estimates of body mass and limb length, and relative hindlimb length (the residuals of the relationship between hind- and forelimb length). Fast-running species had hindlimbs that were long compared to their forelimbs. None of the other size or shape variables showed a significant relationship with speed or endurance. We conclude that the evolution of sprint capacity may be constrained by the need for endurance capacity and vice versa, but the design conflict underlying this trade-off has yet to be identified. Corresponding Editor: T. Garland Jr.

Altitudinal variation of the thermal biology and running performance in the lizard Podarcis tiliguerta

SummaryWe studied, in the field and laboratory, aspects of the thermal biology in two populations of the lizard Podarcis tiliguerta along a 1450 m altitudinal gradient. Body temperatures (Tb) at high altitudes average lower, are more variable, but are more elevated above environmental temperatures than at sea level. Lizards partially reduced the impact of altitudinal changes in thermal loads through presumable subtle behavioural adjustments. A comparison of the thermal preferences in the laboratory, the maximal operative temperatures predicted from a biophysical model, and the activity Tbs at both sites, indicates that the main response to changing environmental conditions is an active shift in thermoregulatory set points. Integration of field Tbs and laboratory data on temperature specific sprint speeds, predicts that the mountainous lizards experience reduced running abilities that are especially acute in the early morning. Despite this impairment of running performance, the thermal sensitivity of running speed has not evolved to match the Tbs experienced by both populations. This result supports the view that the thermal physiology of this lizard is evolutionarily conservative, but the lack of information on the relation between running performance and fitness components impedes rejection of alternative hypotheses.

LOCOMOTOR COMPENSATION CREATES A MISMATCH BETWEEN LABORATORY AND FIELD ESTIMATES OF ESCAPE SPEED IN LIZARDS: A CAUTIONARY TALE FOR PERFORMANCE-TO-FITNESS STUDIES

Abstract A key assumption in evolutionary studies of locomotor adaptation is that standard laboratory measures of performance accurately reflect what animals do under natural circumstances. One widely examined measure of performance is maximum sprint speed, which is believed to be important for eluding predators, capturing prey, and defending territories. Previous studies linking maximum sprint speed to fitness have focused on laboratory measurements, and we suggest that such analyses may be appropriate for some species and intraspecific classes, but not others. We provide evidence for a general inverse relationship between maximum laboratory sprint speed and the percentage of maximum capacity that animals use when escaping from a threat in the field (the model of locomotor compensation). Further, absolute values of field escape speed and maximum laboratory speed are not significantly related when comparing across a diverse group of Anolis and lacertid lizards. We show that this pattern of locomotor compensation holds both within (i.e., among intraspecific classes) and among lizard species (with some exceptions). We propose a simple method of plotting field escape speed (y‐axis) versus maximum laboratory speed (x‐axis) among species and/or intraspecific classes that allows researchers to determine whether their study organisms are good candidates for relating laboratory performance to fitness. We suggest that species that reside directly on, or near the “best fitness line”(field escape speed = maximum laboratory speed) are most likely to bear fruit for such studies.

Sexual Dimorphism of Head Size in Podarcis Hispanica Atrata: Testing the Dietary Divergence Hypothesis By Bite Force Analysis

Sexual dimorphism of relative head size is a widespread phenomenon in lizards, males having larger head/trunk ratios than females. In an attempt to explain this sexual dimorphism several hypotheses have been formulated. The two most frequently cited ones are: 1) sexual selection acting on those structures important in intrasexual competition and 2) natural selection for reduction of food competition between the sexes. In the insular subspecies of Podarcis hispanica (P h. atrata) males tend to have significantly larger heads than similarly sized females. We here test an implicit assumption of the dietary divergence hypothesis, namely that an increase in head size results in an increase in gape width and/or bite force, thereby allowing the larger headed sex to exploit larger prey classes. Using a static bite force model, we calculated the magnitude of bite forces for given directions at given positions on the jaws and for different head sizes. We experimentally determined the hardness of three different prey items and compared the data to the maximal bite force produced by both sexes. Our results suggest an important difference in male and female bite capacity, which may bear significant ecological relevance, and are in agreement with the implicit assumption of the dietary divergence theory.

Selected body temperatures in the lizard Lacerta vivipara: variation within and between populations

Abstract 1. 1.|Selected body temperatures (SBT) of adult male, female and subadult Lacerta vivipara from a Belgian population, were measured monthly in a laboratory thermogradient. 2. 2.|Monthly mean SBTs varied between 29.9 and 34.0°C and differed significantly among months in all three lizard groups, and among lizard groups in 4 out of 6 months. 3. 3.|Evidence for a positive relationship between monthly SBT and air temperature was found in the subadults, but not in the adult lizards. 4. 4.|Monthly mean SBTs measured in this study were consistently higher (mean difference = 2.0°C) than those obtained by Patterson and Davies (1978) in a similar study on Lacerta vivipara from southern England.

Effects of habitat fragmentation on provisioning rates, diet and breeding success in two species of tit (great tit and blue tit)

Abstract The aim of this study was to examine the effects of forest fragmentation on the ability of parent birds to provide their young with an adequate food supply. To examine whether prey population densities of the great tit (Parus major L.) and the blue tit (P. caeruleus L.) vary between study areas in different forest size classes we compared provisioning rates and chick diet and related these parameters to breeding success. We filmed 217 nests over two breeding seasons and collected data on frass fall as a general estimate of caterpillar availability. Nests which were attended by none or one parent only during filming (n = 46) were excluded from the analyses. In both years and for both species feeding rates were highest in the smallest fragments and lowest in the large forest. There was also a suggestion that differences in feeding rates between areas vary between years. We found no consistent tendency for prey size to change with forest size, although both species brought slightly smaller prey items to the nest in the smallest forest fragments and feeding rates correlated negatively with prey size. Caterpillars were the main item fed to nestlings, in both species. We found no evidence to suggest that either frass fall or the proportion of caterpillars in the diet varied with forest size. There was also no correlation between mean frass fall and the total number of caterpillars brought to the nests, in either species. Breeding success, as measured by clutch size, brood size, fledging weight and fledging success, did not differ between the small fragments and the large forest, in either species. There was also no relationship between provisioning rate (as concerns volume of prey fed to nestlings and the quality of chick diet) and breeding success parameters. In conclusion, this study does not suggest suboptimal foraging or breeding conditions in small fragments compared to a nearby large forest, for either species.

The quick and the fast: the evolution of acceleration capacity in Anolis lizards.

Abstract Although of prime ecological relevance, acceleration capacity is a poorly understood locomotor performance trait in terrestrial vertebrates. No empirical data exist on which design characteristics determine acceleration capacity among species and whether these design traits influence other aspects of locomotor performance. In this study we explore how acceleration capacity and sprint speed have evolved in Anolis lizards. We investigate whether the same or different morphological traits (i.e., limb dimensions and muscle mass) correlate with both locomotor traits. Within our sample of Anolis lizards, relative sprint speed and acceleration capacity coevolved. However, whereas the variation in relative acceleration capacity is primarily explained by the variation in relative knee extensor muscle mass, the variation in relative sprint speed is correlated to the variation in relative femur, tibia, and metatarsus length as well as knee extensor muscle mass. The fact that the design features required to excel in either performance trait partly overlap might explain the positive correlation between the variation in relative sprint speed and acceleration capacity. Furthermore, our data show how similar levels of sprint performance can be achieved through different morphological traits (limb segment lengths and muscle mass) suggesting that redundant mapping has potentially played a role in mitigating trade‐offs.

Evolutionary maintenance of sexual dimorphism in head size in the lizard Zootoca vivipara: a test of two hypotheses

Zootoca vivipara is a small lizard that shows sexual dimorphism in head size. Males have larger heads than females of the same body size. By observing matings and aggressive interactions between males in the laboratory, we investigated whether this sexual dimorphism could be the result of intra- and/or intersexual selection. Winners of male–male interactions had larger heads than losers. During mating attempts, males with larger heads succeeded in grasping a female faster than males with smaller heads. It follows that head size in Z. vivipara may affect male reproductive success both through intrasexual competition (fighting ability) and through intersexual selection (grasping ability). This suggests that sexual selection may be the cause for the sexual dimorphism in head size in this species.

Morphology, performance, behavior and ecology of three color morphs in males of the lizard Podarcis melisellensis

Males of a Croatian population of the lacertid lizard Podarcis melisellensis exhibit a striking polymorphism, with coloration of the throat and abdomen ranging from completely white, to yellow or orange. In a first attempt to explore the potential ecological and evolutionary significance of this polymorphism, we compared the three forms of males in aspects of their morphology, whole-animal performance, behavior, and ecology. Orange males are, on average, larger in snout-vent length and have disproportionately larger heads than either white or yellow males. This is reflected in orange males having higher bite force capacity and theoretically an increased access to harder prey. Residual limb length, maximal sprint speed and maximal exertion do not differ among color morphs. Body temperatures in the field are similar in the three morphs, but yellow males are caught at sites with slightly higher air temperatures than are orange and white males. Behavioral observations show no differences in time budgets or in the timing of activities among morphs. Microhabitat use is also similar in the three color morphs, but orange males were more often initially seen on rocky substrates. Our findings suggest that the observed polymorphism likely does not originate from a divergence in niche or use of resources, but possibly reflects an underlying polymorphism in mating tactics.