Search

Species vary extensively in geographic range size and climatic niche breadth. If range limits are primarily determined by climatic factors, species with broad climatic tolerances and those that track geographically widespread climates should have large ranges. However, large ranges might increase the probability of population fragmentation and adaptive divergence, potentially decoupling climatic niche breadth and range size. Conversely, ecological generalism in large-ranged species might lead to higher gene flow across climatic transitions, increasing species' cohesion and thus decreasing genetic isolation by distance (IBD). Focusing on Australia's iconic

Animals use mating traits to compete for, attract, and choose mates. Because mating traits influence mate choice, the divergence of mating traits between populations can result in reproductive isolation. This can occur without associated morphological divergence, producing reproductively isolated cryptic species that are visually indistinguishable. Thus, identifying the mating traits in morphologically conservative groups is key to resolving diversity and speciation processes. Lizards contain many such groups, with phylogeographic studies often revealing highly divergent but morphologically cryptic lineages within species. Considering that cryptic lizard species can be sympatric but morphologically indistinguishable, we hypothesize that candidate species will exhibit divergent pheromones and that pheromones will have typically diverged more than morphology. To test this, we used gas chromatography to characterize pheromones (epidermal pore secretions) from 10 genetically divergent lineages of the Bynoe's gecko (Heteronotia binoei) species complex in northern Australia. Multivariate analyses of pheromone blends and morphology indicate that pheromones are lineage specific and have diverged relatively more than morphology. Such specificity suggests that pheromones influence behavioral isolation in this morphologically conservative lizard radiation. These results suggest that pheromone data may unlock the tremendous cryptic diversity currently being uncovered in many lizard groups.

Adaptive radiation is a widely recognized pattern of evolution wherein substantial phenotypic change accompanies rapid speciation. Adaptive radiation may be triggered by environmental opportunities resulting from dispersal to new areas or via the evolution of traits, called key innovations, that allow for invasion of new niches. Species sampling is a known source of bias in many comparative analyses, yet classic adaptive radiations have not been studied comparatively with comprehensively sampled phylogenies. In this study, we use unprecedented comprehensive phylogenetic sampling of Anolis lizard species to examine comparative evolution in this well-studied adaptive radiation. We compare adaptive radiation models within Anolis and in the Anolis clade and a potential sister lineage, the Corytophanidae. We find evidence for island (i.e., opportunity) effects and no evidence for trait (i.e., key innovation) effects causing accelerated body size evolution within Anolis. However, island effects are scale dependent: when Anolis and Corytophanidae are analyzed together, no island effect is evident. We find no evidence for an island effect on speciation rate and tenuous evidence for greater speciation rate due to trait effects. These results suggest the need for precision in treatments of classic adaptive radiations such as Anolis and further refinement of the concept of adaptive radiation.

We report a new chameleon-like Anolis species from Hispaniola that is ecomorphologically similar to congeners found only on Cuba. Lizards from both clades possess short limbs and a short tail and utilize relatively narrow perches, leading us to recognize a novel example of ecomorphological matching among islands in the well-known Greater Antillean anole radiation. This discovery supports the hypothesis that the assembly of island faunas can be substantially deterministic and highlights the continued potential for basic discovery to reveal new insights in well-studied groups. Restricted to a threatened band of midelevation transitional forest near the border of the Dominican Republic and Haiti, this new species appears to be highly endangered.

Identification of mechanisms that promote variation in life-history traits is critical to understand the evolution of divergent reproductive strategies. Here we compiled a large life-history data set (674 lizard populations, representing 297 species from 263 sites globally) to test a number of hypotheses regarding the evolution of life-history traits in lizards. We found significant phylogenetic signal in most life-history traits, although phylogenetic signal was not particularly high. Climatic variables influenced the evolution of many traits, with clutch frequency being positively related to precipitation and clutches of tropical lizards being smaller than those of temperate species. This result supports the hypothesis that in tropical and less seasonal climates, many lizards tend to reproduce repeatedly throughout the season, producing smaller clutches during each reproductive episode. Our analysis also supported the hypothesis that viviparity has evolved in lizards as a response to cooler climates. Finally, we also found that variation in trait values explained by clade membership is unevenly distributed among lizard clades, with basal clades and a few younger clades showing the most variation. Our global analyses are largely consistent with life-history theory and previous results based on smaller and scattered data sets, suggesting that these patterns are remarkably consistent across geographic and taxonomic scales.

Reproductive phenology often varies geographically within species, driven by environmental gradients that alter growth and reproduction. However, environments can differ between adjacent habitats at single localities. In lowland Puerto Rico, both open (sunny, warm) and forested (shady, cool) habitats may be only meters apart. The lizard Anolis cristatellus lives in both habitats: it thermoregulates carefully in the open but is a thermoconformer in the forest. To determine whether reproduction differs between habitats, we compared reproductive cycles of females in open versus forest habitats at two localities for over 2 years. Open females were more likely than forest females to be reproductive throughout the year, probably because open females were able to bask and thereby achieve warmer body temperatures. These between-habitat differences in reproduction were especially marked in cool months and are equivalent in magnitude to those between populations separated by elevation. Thus, environmental differences (even on a microlandscape scale) matter to reproduction and probably to demography.

Glucocorticoid hormone profiles are increasingly used as physiological markers to infer the strength of species interactions that can influence fitness and ensuing population dynamics of animals. Here we investigated two aims. First, we measured the effect of a 90-min capture stress protocol on the plasma corticosterone responses of a large native Australian lizard, the lace monitor (Varanus varius). Second, we compared the basal and postcapture stress corticosterone responses of lace monitors in habitats where they were exposed to high or low densities of the European red fox (Vulpes vulpes), an introduced competitor. Lace monitors responded to the capture stress protocol by significantly increasing plasma levels of corticosterone above basal at 45- and 90-min-postcapture blood-sampling intervals. In habitats with high fox densities, lace monitors produced a significantly greater basal and capture-stress-induced corticosterone response compared to individuals in low-fox density habitat. A significant interaction among fox density, time postcapture, and body condition was also found to influence plasma corticosterone values. These results suggest competition with red fox, perhaps via nutritional stress and increased hypersensitivity of the adrenocortical axis in lizards. At present, without further research, we do not understand whether such responses mediate lizard fitness or whether they have adaptive or maladaptive consequences for lizard populations in response to red fox competition. Nevertheless, our results help broaden understanding of the physiological implications arising from species interactions and specifically how introduced competitors could mediate diverse impacts on native biodiversity.

Invasive species often encounter novel climatic conditions when they spread outside of their native ranges. Invading populations can respond to novel conditions by acclimation or adaptation of physiological capacities, which may facilitate their spread. We investigated differences in physiological traits among three populations of an invasive lizard, the brown anole (Anolis sagrei), along the latitudinal extent of its invasion in the southeastern United States. We predicted latitudinal clines for most traits based on models of adaptation to climate. Consistent with the latitudinal cline in temperature and moisture, the mean critical thermal minimum and the mean rate of water loss were lowest for lizards in the northern population. Furthermore, these traits acclimated to either temperature or humidity in a direction consistent with adaptive phenotypic plasticity. By contrast, metabolic rates varied among populations but did not conform to our prediction based on a latitudinal cline in temperature. Critical thermal maxima, endurances, and sprint speeds were similar among populations. Despite the idea that tropical lizards have limited capacity for acclimation, we found variation among invasive populations of brown anoles, which could have partially resulted from acclimation. This physiological variation within the invasive range raises questions about the roles of plasticity and adaptation in the success of the invasion.

The ability to shed an appendage occurs in both vertebrates and invertebrates, often as a tactic to avoid predation. The tails of lizards, unlike most autotomized body parts of animals, exhibit complex and vigorous movements once disconnected from the body. Despite the near ubiquity of autotomy across groups of lizards and the fact that this is an extraordinary event involving the self-severing of the spinal cord, our understanding of why and how tails move as they do following autotomy is sparse. We herein explore the histochemistry and physiology of the tail muscles of the leopard gecko (Eublepharis macularius), a species that exhibits vigorous and variable tail movements following autotomy. To confirm that the previously studied tail movements of this species are generally representative of geckos and therefore suitable for in-depth muscle studies, we quantified the three-dimensional kinematics of autotomized tails in three additional species. The movements of the tails of all species were generally similar and included jumps, flips, and swings. Our preliminary analyses suggest that some species of gecko exhibit short but high-frequency movements, whereas others exhibit larger-amplitude but lower-frequency movements. We then compared the ATPase and oxidative capacity of muscle fibers and contractile dynamics of isolated muscle bundles from original tails, muscle from regenerate tails, and fast fibers from an upper limb muscle (iliofibularis) of the leopard gecko. Histochemical analysis revealed that more than 90% of the fibers in original and regenerate caudal muscles had high ATPase but possessed a superficial layer of fibers with low ATPase and high oxidative capacity. We found that contraction kinetics, isometric force, work, power output, and the oscillation frequency at which maximum power was generated were lowest in the original tail, followed by the regenerate tail and then the fast fibers of the iliofibularis. Muscle from the original tail exhibited greater resistance to fatigue, followed by the regenerate tail and then the fast iliofibularis fibers. These results suggest that the relatively slow and oxidative fibers found within the tail musculature have a significant impact on contractile function, which translates into a trade-off between longevity of performance and power after autotomy.

Caudal autotomy is a common defense mechanism in lizards, where the animal may lose part or all of its tail to escape entrapment. Lizards show an immense variety in the degree of investment in a tail (i.e., length) across species, with tails of some species up to three or four times body length (snout-vent length [SVL]). Additionally, body size and form also vary dramatically, including variation in leg development and robustness and length of the body and tail. Autotomy is therefore likely to have fundamentally different effects on the overall body form and function in different species, which may be reflected directly in the incidence of lost/regenerating tails within populations or, over a longer period, in terms of relative tail length for different species. We recorded data (literature, museum specimens, field data) for relative tail length (n=350 species) and the incidence of lost/regenerating tails (n=246 species). We compared these (taking phylogeny into account) with intrinsic factors that have been proposed to influence selective pressures acting on caudal autotomy, including body form (robustness, body length, leg development, and tail specialization) and ecology (foraging behavior, physical and temporal niches), in an attempt to identify patterns that might reflect adaptive responses to these different factors. More gracile species have relatively longer tails (all 350 spp., P0.001; also significant for five of the six families tested separately), as do longer (all species, P0.001; Iguanidae, P0.05; Lacertidae, P0.001; Scindidae, P0.001), climbing (all species, P0.05), and diurnal (all species, P0.01; Pygopodidae, P0.01) species; geckos without specialized tails (P0.05); or active-foraging skinks (P0.05). We also found some relationships with the data for caudal autotomy, with more lost/regenerating tails for nocturnal lizards (all 246 spp., P0.01; Scindidae, P0.05), larger skinks (P0.05), climbing geckos (P0.05), or active-foraging iguanids (P0.05). The selective advantage of investing in a relatively longer tail may be due to locomotor mechanics, although the patterns observed are also largely consistent with predictions based on predation pressure.

Lizards that undergo caudal autotomy experience a variety of consequences, including decreased locomotor performance in a number of cases. One mode of locomotion common to many arboreal lizard species is jumping, and yet little is known about the effects of autotomy on this locomotor mode. In this article we review recent literature demonstrating the importance of the lizard tail as an in-air stabilizer. First, we review work highlighting how a variety of lizards from diverse families can use their tails to control body position in midair. We then move on to cover recent work demonstrating how in at least one species, Anolis carolinensis, tail loss can lead to remarkable instabilities after takeoff during jumping. Such instabilities occur even when animals are jumping toward specific targets both below and above them, although individual variation in the response to tail loss is considerable. Finally, we report results from a study examining whether increased jumping experience after autotomy facilitates the recovery of in-air stability during jumping. Our work suggests it does not, at least not consistently after 5 wk, indicating that any fitness consequences associated with decreased jumping stability are likely to be long term.

Immune defenses are of great benefit to hosts, but reducing the impact of infection by mounting an immune response also entails costs. However, the physiological mechanisms that generate the costs of an immune response remain poorly understood. Moreover, the majority of studies investigating the consequences of an immune challenge in vertebrates have been conducted on mammals and birds. The aim of this study is to investigate the physiological costs of mounting an immune response during gestation in an ectothermic species. Indeed, because ectothermic species are unable to internally regulate their body temperature, the apportionment of resources to homeostatic activities in ectothermic species can differ from that in endothermic species. We conducted this study on the common lizard Zootoca vivipara. We investigated the costs of mounting an immune response by injecting females with sheep red blood cells and quantified the consequences to reproductive performance (litter mass and success) and physiological performance (standard metabolic rate, endurance, and phytohemagglutinin response). In addition, we measured basking behavior. Our analyses revealed that mounting an immune response affected litter mass, physiological performance, and basking behavior. Moreover, we demonstrated that the modulation of an immune challenge is impacted by intrinsic factors, such as body size and condition.

The predominant view is that the thermal physiology of tropical ectotherms, including lizards, is not labile over ecological timescales. We used the recent introduction (∼35 years ago) of the Puerto Rican lizard Anolis cristatellus to Miami, Florida, to test this thermal rigidity hypothesis. We measured lower (critical thermal minimum [CT(min)]) and upper (critical thermal maximum [CT(max)]) thermal tolerances and found that the introduced population tolerates significantly colder temperatures (by ∼3°C) than does the Puerto Rican source population; however, CT(max) did not differ. These results mirror the thermal regimes experienced by each population: Miami reaches colder ambient temperatures than Puerto Rico, but maximum ambient temperatures are similar. The differences in CT(min) were observed even though lizards from both sites experienced nearly identical conditions for 49 days before CT(min) measurement. Our results demonstrate that changes in thermal tolerance occurred relatively rapidly (∼35 generations), which strongly suggests that the thermal physiology of tropical lizards is more labile than previously proposed.

The use of stored resources to fuel reproduction, growth, and self-maintenance in the face of uncertain nutrient availability is a tactic common to many organisms. The degree to which organisms rely on stored resources in response to varied nutrients, however, is not well quantified. In this study, we used stable isotope methods to quantify the use of stored versus incoming nutrients to fuel growth and egg and fat body development in lizards under differing nutrient regimes. We found that the degree of capital breeding is a function of an individual's body condition. Furthermore, given sufficient income, lizards in poor condition can allocate simultaneously to storage, growth, and reproduction and "catch up" in body size and reproductive allocation to better-conditioned animals. Using natural variation in the δ(13)C of environmental nutrient pulses, we also found a high degree of variation in capital breeding in a lizard community. These findings demonstrate that capital breeding in lizards is not simply a one-way flow of endogenous stores to eggs but is a function of the condition state of individuals and seasonal nutrient availability. We use our findings to comment on capital breeding in lizards and the utility of the capital-income concept in general.

Net energy availability depends on plasma corticosterone concentrations, food availability, and their interaction. Limited net energy availability requires energy trade-offs between self-maintenance and reproduction. This is important in matrotrophic viviparous animals because they provide large amounts of energy for embryos, as well as self-maintenance, for the extended period of time during gestation. In addition, gravid females may transmit environmental information to the embryos in order to adjust offspring phenotype. We investigated effects of variation in maternal plasma corticosterone concentration and maternal food availability (2 × 2 factorial design) during gestation on offspring phenotype in a matrotrophic viviparous lizard (Pseudemoia entrecasteauxii). Subsequently, we tested preadaptation of offspring phenotype to their postnatal environment by measuring risk-averse behavior and growth rate using reciprocal transplant experiments. We found that maternal net energy availability affected postpartum maternal body condition, offspring snout-vent length, offspring mass, offspring performance ability, and offspring fat reserves. Females treated with corticosterone allocated large amounts of energy to their own body condition, and their embryos allocated more energy to energy reserves than somatic growth. Further, offspring from females in high plasma corticosterone concentration showed compensatory growth. These findings suggest that while females may be selfish when gestation conditions are stressful, the embryos may adjust their phenotype to cope with the postnatal environment.

Carbon stable isotope (delta(13)C) analysis can be used to infer the origin and to estimate the flow of nutrient resources through animals and across ecological compartments. These applications require knowledge of the rates at which carbon is incorporated into animal tissues and diet-to-tissue discrimination factors (Delta(13)C). Studies of carbon dynamics in terrestrial vertebrates to date have focused almost solely on endothermic animals; ectotherms such as reptiles have received little attention. Here we determined carbon incorporation rates and Delta(13)C in tissues of prairie lizards (Sceloporus undulatus consobrinus) and collared lizards (Crotaphytus collaris). The smaller lizard, S. undulatus, had carbon retention times of 25 and 61 d in plasma and red blood cells (RBC), respectively, compared with 44 and 311 d for the larger C. collaris. Liver, muscle, and skin carbon retention times for S. undulatus were 21, 81, and 94 d. Growth contributed 9%-19% of the carbon incorporated into these tissues. This contribution is similar to endotherms measured at comparable developmental stages. Mean Delta(13)C for plasma (-0.2 per thousand +/- 0.4 per thousand Vienna Pee Dee Belemnite Standard) and RBCs (-1.3 per thousand +/- 0.8 per thousand) were similar to values reported for other vertebrates. Carbon incorporation rates for these ectotherms, however, are seven times slower than in similarly sized adult endotherms. Although a limited comparison with data for warm-water fishes suggests comparable incorporation rates between aquatic and terrestrial ectotherms, this study highlights the lack of experimental data for isotope dynamics in ectotherms across a range of temperatures, body sizes, and developmental stages.

Stress experienced by a reproducing female can substantially affect the morphology, behavior, and physiology (and hence fitness) of her offspring. In addition, recent studies demonstrate that stress hormones (corticosterone) influence sex determination of embryos. To explore these issues, we manipulated corticosterone levels in eggs of two Australian lizard species (Amphibolurus muricatus and Bassiana duperreyi) that exhibit temperature-dependent sex determination (TSD). Elevated corticosterone levels during embryonic development affected body size, growth rates, and sex ratios of the resultant offspring, but the direction and magnitude of these effects differed between the species. Corticosterone enhanced growth rates of hatchling B. duperreyi but inhibited growth of A. muricatus. Eggs with elevated levels of corticosterone produced more daughters in A. muricatus and more sons in B. duperreyi. The sex-ratio effect in A. muricatus may have been due to sex-specific embryonic mortality, but it may represent a direct effect on sex determination in B. duperreyi (because embryonic mortality was not affected by corticosterone manipulation in this species). These results demonstrate the complexity of proximate mechanisms for sex determination among reptiles with TSD and illustrate the potential role of corticosterone in sex-determining systems.

Some species of terrestrial lizards in wet-dry tropical climates reduce their body temperatures (T(b)'s) and activity and lower their metabolic rates during the dry season when food and water resources are scarce. However, semiaquatic lizards have access to water and presumably food throughout the year, so it is possible that they will not have the seasonal response seen in terrestrial species. We studied the thermal biology, energetics, and water flux of Varanus indicus, a semiaquatic, mangrove-dwelling varanid in tropical northern Australia. Although V. indicus remained active all year, they reduced their activity in the dry season, but not to the extent of terrestrial varanids. Varanus indicus field metabolic rates decreased by 38% in the dry season mostly as a result of the reduction in activity. Although food and water depletion are the driving forces behind decreases in dry season T(b) selection and energetics for many varanids, V. indicus appears not to be subject to these pressures to the same extent. Thermoregulatory indices indicate that V. indicus actively thermoregulate in the wet and dry seasons, but they do not fully exploit the available thermal resources. These lizards are unusual among varanid lizards in that their midday T(b)'s are relatively low (about 31 degrees C) despite the availability of thermal resources that would allow them to attain substantially higher T(b)'s.

I present a dynamic bioenergetic model that couples individual energetics and population dynamics to predict current lizard ranges and those following climate warming. The model predictions are uniquely based on first principles of morphology, life history, and thermal physiology. I apply the model to five populations of a widespread North American lizard, Sceloporus undulatus, to examine how geographic variation in traits and life histories influences ranges. This geographic variation reflects the potential for species to adapt to environmental change. I then consider the range dynamics of the closely related Sceloporus graciosus. Comparing predicted ranges and actual current ranges reveals how dispersal limitations, species interactions, and habitat requirements influence the occupied portions of thermally suitable ranges. The dynamic model predicts individualistic responses to a uniform 3 degrees C warming but a northward shift in the northern range boundary for all populations and species. In contrast to standard correlative climate envelope models, the extent of the predicted northward shift depends on organism traits and life histories. The results highlight the limitations of correlative models and the need for more dynamic models of species' ranges.

The eggs of birds and reptiles contain detectable levels of several steroid hormones, and experimental application of such steroids can reverse genetically determined sex of the offspring. However, any causal influence of maternally derived yolk steroids on sex determination in birds and reptiles remains controversial. We measured yolk hormones (dihydrotestosterone, testosterone, and 17 beta-estradiol) in newly laid eggs of the montane scincid lizard Bassiana duperreyi. This species is well suited to such an analysis because (1) offspring sex is influenced by incubation temperatures and egg size as well as by sex chromosomes, suggesting that yolk hormones might somehow be involved in the complex pathways of sex determination, and (2) experimental application of either estradiol or fadrozole to such eggs strongly influences offspring sex. We obtained yolk by biopsy, before incubating the eggs at a temperature that produces a 50:50 sex ratio. Yolk steroid levels varied over a threefold range between eggs from different clutches, but there were no significant differences in yolk steroids, or in relative composition of steroids, between eggs destined to become male versus female. Further, yolk steroid concentrations were not significantly related to egg size. Thus, yolk steroid hormones do not appear to play a critical role in sex determination for B. duperreyi.

In territorial polygynous taxa, reproductive success reflects phenotypic variation. Using Crotaphytus collaris, a sexually dimorphic lizard in which males use the head (i.e., jaws and associated musculature) as a weapon when territorial interactions escalate to fights, we tested the hypothesis that weapon performance (i.e., bite force) is a better predictor of fitness than body or weapon size. Bite-force performance predicted the number of female home ranges overlapped, estimated mating success, and potential reproductive output. However, no body or weapon size measure correlated with these estimates of fitness, and only one weapon dimension (head width) correlated with bite force. These results indicate that weapon performance has far stronger effects on fitness than body or weapon size, likely because it directly influences fight outcomes. As such, it is desirable that the use of morphology as a proxy for performance and its presumed extensions to fitness be based on empirical morphology-performance relationships.

Offspring phenotype can be affected by maternal history before and during gestation. Offspring sensitivity to maternal conditions is believed to have evolved to favor preadaptation of offspring to environmental factors they are likely to encounter. Because the locomotor capacity of an individual is likely to have important fitness consequences, we examined the role of long-term and short-term prenatal conditions on offspring's locomotor performance in the lizard Lacerta vivipara. To examine long-term prenatal effects, we manipulated the density of two populations, leaving two additional populations as unmanipulated. We then collected pregnant females within these four populations (Cévennes, Massif Central, France) and kept them in the laboratory until parturition. To examine short-term prenatal effects, we manipulated the corticosterone level of half the females within each population. We took two different measurements of offspring locomotion: sprint speed and endurance. As already documented, sprint speed was positively correlated with offspring body size. Although population density significantly affected female fecundity, neither the density manipulation nor the population of origin influenced offspring phenotype. Corticosterone administered during gestation decreased juvenile sprint speed but did not affect juvenile endurance. Furthermore, we observed that the motivation to run was influenced by maternal hormonal treatment. Juveniles born from corticosterone-treated mothers needed more stimuli than those born from control mothers. We conclude, therefore, that the action of corticosterone on sprint speed could be more behavioral than physiological. Offspring phenotype as measured by endurance and sprint speed appeared partly under maternal control.

The structure of communities may be largely a result of evolutionary changes that occurred many millions of years ago. We explore the historical ecology of squamates (lizards and snakes), iden- tify historically derived differences among clades, and examine how this history has affected present-day squamate assemblages globally. A dietary shift occurred in the evolutionary history of squamates. Iguanian diets contain large proportions of ants, other hymenop- terans, and beetles, whereas these are minor prey in scleroglossan lizards. A preponderance of termites, grasshoppers, spiders, and in- sect larvae in their diets suggests that scleroglossan lizards harvest higher energy prey or avoid prey containing noxious chemicals. The success of this dietary shift is suggested by dominance of sclero- glossans in lizard assemblages throughout the world. One sclero- glossan clade, Autarchoglossa, combined an advanced vomeronasal chemosensory system with jaw prehension and increased activity levels. We suggest these traits provided them a competitive advantage during the day in terrestrial habitats. Iguanians and gekkotans shifted to elevated microhabitats historically, and gekkotans shifted activity to nighttime. These historically derived niche differences are apparent in extant lizard assemblages and account for some observed structure. These patterns occur in a variety of habitats at both regional and local levels throughout the world.

It is notoriously difficult to test hypotheses about the selective forces responsible for major phylogenetic transitions in life-history traits, but the evolution of viviparity (live bearing) in reptiles offers an ideal model system. Viviparity has arisen in many oviparous reptile lineages that have invaded colder climates. Thermal advantages (eggs retained within the mother's body will be warmer than those laid in the nest) are almost certainly important, but the actual selective pressures remain controversial. For example, the benefit to retention might involve faster development, protection against freezing, predation, or desiccation, or modification of hatchling phenotypes. I experimentally manipulated incubation regimes of a montane scincid lizard (Bassiana duperreyi, Scincidae) to test these ideas. Eggs maintained in cooler "nests" in the laboratory developed more slowly, were more likely to die before hatching, and produced inferior (small, slow) hatchlings. A 2-wk initial period of higher-temperature incubation (simulating uterine retention, an intermediate step toward viviparity) ameliorated these effects. In the field, I placed eggs in artificial nests at the upper elevational limit of natural nests and also extending a further 100 m higher on the mountain. The results mirrored those in the laboratory: retention at maternal body temperatures accelerated hatching, enhanced hatching success, and increased locomotor speeds of hatchlings. This selective advantage of uterine retention was greater at higher elevations and increased with longer retention. The causal process responsible was prolonged low-temperature incubation rather than freezing, desiccation, or predation, and both hatching success and hatchling viability were affected. Field experiments that directly re-create selective regimes may thus provide robust tests of adaptationist hypotheses.

The study of adaptive radiations has played a funda- mental role in understanding mechanisms of evolution. A recent resurgence in the study of adaptive radiations highlights a gap in our knowledge about determining whether a clade constitutes adap- tive diversification. Specifically, no objective criteria exist to judge whether a clade constitutes an adaptive radiation. Most clades, given enough time, will diversify adaptively to some extent; therefore, we argue that the term "adaptive radiation" should be reserved for those clades that are exceptionally diverse in terms of the range of habitats occupied and attendant morphological adaptations. Making such a definition operational, however, requires a comparative analysis of many clades. Only by comparing clades can one distinguish those that are exceptionally diverse (or nondiverse) from those exhibiting a normal degree of adaptive disparity. We propose such a test, fo- cusing on disparity in the ecological morphology of monophyletic groups within the lizard family Iguanidae. We find that two clades, the Polychrotinae and Phrynosomatinae, are exceptionally diverse and that two others, the Crotaphytinae and Oplurinae, are excep- tionally nondiverse. Potential explanations for differences in diversity are discussed, as are caveats and future extensions of our approach.

Heliothermy (heat gain by radiation) has been given a prominent role in basking lizards. However, thigmothermy (heat gain by conduction) could be relevant for heating in small lizards. To ascertain the importance of the different heat transmission modes to the thermoregulatory processes, we conducted an experimental study where we analyzed the role of heat transmission modes on heating rates and on the selection of sites for heating in the Mediterranean lizard Acanthodactylus erythrurus (Lacertidae). The study was conducted under laboratory conditions, where two situations of different operative temperatures (38 degrees and 50 degrees C) were simulated in a terrarium. In a first experiment, individuals were allowed to heat up during 2 min at both temperatures and under both heat transmission modes. In a second experiment, individuals were allowed to select between patches differing in the main transmission mode, at both temperatures, to heat up. Experiences were conducted with live, nontethered lizards with a starting body temperature of 27 degrees C. Temperature had a significant effect on the heating rate, with heat gain per unit of time being faster at the higher operative temperature (50 degrees C). The effect of the mode of heat transmission on the heating rate was also significant: at 50 degrees C, heating rate was greater when the main heat transmission mode was conduction from the substrate (thigmothermy) than when heating was mainly due to heat gain by radiation (heliothermy); at 38 degrees C, heating rates did not significantly differ between transmission modes. At 38 degrees C, selection of the site for heating was not significantly different from that expected by chance. However, at 50 degrees C, the heating site offering the slowest heating rate (heliothermic patch) was selected. These results show that heating rates vary not only with environmental temperature but also with different predominant heat transmission modes. Lizards are able to identify and exploit this heterogeneity, selecting the source of heat gain (radiation) that minimizes the risk of overheating when temperature is high.

To understand the evolution of biological traits, information on the degree and origins of intraspecific variation is essential. Because adaptation can take place only if the trait shows heritable variation, it is important to know whether (at least) part of the trait variation is genetically based. We describe intra- and interindividual variation in three performance measures (sprint speed, climbing, and clambering speed) in juvenile Gallotia galloti lizards from three populations and examine how genetic, environmental (incubation temperature), and ontogenetic (age, size) effects interact to cause performance variation. Moreover, we test whether the three performance traits are intercorrelated phenotypically and genetically. Sprint speed is highest in juveniles incubated at the lowest temperature (26 degrees C) irrespective of population. Climbing speed differs among populations, and the differences persist at least until the lizards are 30 wk old. This suggests that the three populations experience different selective pressures. Moreover, mass, snout-vent length, and hindlimb length seem to affect climbing performance differently in the three populations. The variation in sprinting and climbing ability appears to be genetically based. Moreover, the two performance traits are intercorrelated and thus will not evolve independently from each other. Clambering speed (i.e., capacity to climb up an inclined mesh) varies among individuals, but the origin of this variation remains obscure.

Locomotor performance of lizards and its relationship to the ecology and morphology of the forms concerned has been well studied recently. Asymmetry of limbs might make the body unstable and make performance less effective. However, their effects on terrestrial locomotion remain almost unexplored. In this article, the escape performance of the lizard Psammodromus algirus running at high speed was related to hindlimb morphology and fluctuating asymmetry levels. Femur length was significantly shorter than crus length. However, absolute fluctuating asymmetry in femur length was significantly larger than in crus length. Asymmetry was not related to body or limb size, thus larger individuals or those with longer limbs did not have significantly greater fluctuating asymmetry. Neither body size nor the length of the limbs (femur or crus) were significantly related to any of the variables describing escape performance. However, escape performance was affected by femur-length fluctuating asymmetry, which resulted in significantly reduced overall escape speeds. In contrast, asymmetry in crus length did not affect escape performance. We discuss the possible basis of these alterations of locomotion, the relevance of reduced performance for the ecology of this species, and how individuals may compensate for the costs of asymmetry.

In geographically widespread ectotherms, variation in life history phenotypes may be caused by differences in maintenance metabolism of individuals. I estimated daily and annual maintenance metabolism of eastern fence lizards, Sceloporus undulatus, from two populations with markedly different life histories; lizards in South Carolina grow faster, mature earlier, and have greater annual reproductive output than lizards in New Jersey. I measured diel cycles of resting metabolic rate (RMR) at four temperatures (20 degrees, 30 degrees, 33 degrees, and 36 degrees C) during spring, summer, and fall. In all seasons, RMR increased significantly from 20 degrees to 33 degrees C but did not differ significantly between 33 degrees and 36 degrees C. Adults from New Jersey had a higher RMR than adults from South Carolina in summer and fall but not in spring. Juveniles from South Carolina had a higher RMR than juveniles from New Jersey in summer but not in spring or fall. Annual maintenance metabolism of New Jersey lizards (53.7 kJ) was greater than that of South Carolina lizards (45.8 kJ), despite the shorter duration of activity in New Jersey. I conclude that the difference in maintenance metabolism between populations contributes to the greater production by S. undulatus in South Carolina.

The European common lizard Lacerta vivipara, a reptile of cold-temperate climates, provides us an interesting model of low-temperature adaptation. Indeed its unique cold-hardiness strategy, which employs both freeze tolerance and freeze avoidance, may be seen as the primary reason for its large distribution, which extends from Spain to beyond the Arctic circle. To study the metabolism supporting this capacity, we used three techniques: two techniques of calorimetry (oxygen consumption and thermogenesis) and nuclear magnetic resonance spectroscopy. These techniques were used to examine the metabolic balance and the different molecular pathways used between three different periods through the year (September, January, and May). The results show a significant 20% augmentation of winter anaerobic metabolism compared to other periods of the year. This is mainly because of an activation of the lactic fermentation pathway leading to an increase of lactate concentration (34% in winter). Furthermore, glucose, which increases some 245% in winter, is used as antifreeze and metabolic substrate. Furthermore, this study provides evidence that the physiological adaptations of the common lizard differ from those of other ectotherms such as Rana sylvatica. Concentrations of alanine and glycerol, commonly used as antifreeze by many overwintering ectotherms, do not increase during winter.

Relatively few squamate reptiles oviposit eggs with embryos at developmental stages greater than stage 30. To investigate potential proximate and ultimate bases of this phenomenon, we experimentally induced females of the lizard Urosaurus ornatus to retain their eggs past the normal time of oviposition (NTO). This procedure allowed us to determine whether the length of egg retention is fixed or facultative and to evaluate the effects of retention on embryos, hatchlings, and females. Females were able to retain eggs facultatively for at least 29 d past the NTO. However, retention resulted in arrested development of embryos; arrest occurred at stages 30-30.5, which is only slightly more advanced than that at the NTO (stage 29.5). Embryogenesis was reinitiated when eggs were removed from females and placed in incubation media. Hatching success of these eggs was high (87%), and incubation time was not affected by the number of days that development had been arrested. However, the snout-vent length and water content of hatchlings were negatively related to the length of retention, and they ran slower than hatchlings from control eggs obtained at the NTO. Retention of eggs past the NTO had no detectable effect on the body condition or running speeds of females. Developmental arrest and the adverse effects of retention on hatchling phenotype, if widespread among squamates, would account for the limited range of embryo stages at oviposition and act as major constraints on the evolution of viviparity.

We used a system of neighboring small islands with and without the lizard Anolis sagrei to stage a 7-yr experimental study of the effects of an invading species. Lizard propagules were introduced to four islands, randomly selected from eight that lacked lizards naturally. Four other islands where lizards occurred naturally constituted a third treatment. We examined possible lizard indirect effects on the commonest shrub (via its arthropod herbivores), two sizes of aerial arthropods, and hymenopteran parasitoids. Lizards reduced leaf damage; moreover, during the middle years of the experiment, damage was less on introduction islands than on islands having lizards naturally. Lizards increased the number of small aerial arthropods but had no effect on large aerial arthropods; the full effect on small arthropods was only evident near the end of the experiment. Lizard introduction increased the number of hymenopteran parasitoids at the end of the experiment; however, only islands having lizards naturally had significantly more parasitoids than no-lizard islands summed over the long term. In contrast to the indirect effects, the mostly direct effect of lizards on spiders was very strong; introduction transformed spider density to that on natural lizard islands relatively rapidly and monotonically. In addition to demonstrating how an introduced vertebrate predator can affect food webs even down to the producer level, this study illustrates the greater strength and regularity of direct as opposed to indirect effects.

We analyzed footprints on the surface of a sand dune to estimate maximal running speeds and the incidence of bipedality in nature, as well as to investigate the effects of incline on the escape locomotion of the lizard Callisaurus draconoides. Previous laboratory tests predicted that inclines would negatively affect sprinting performance in C. draconoides. Although physiologists commonly assume that escape locomotion will be near maximal capacity, we found that only 11% of all strides were greater than 90% of maximal speed of C. draconoides. Escape paths averaged 10 m in length and were generally straight. Approximately 30% of the strides taken by C. draconoides were bipedal, and this value was three times greater than previously found for the closely related species Uma scoparia. The modal value of bipedal stride lengths was greater than that for quadrupedal strides. Inclines negatively affected velocity of only the first meter of C. draconoides escape paths. The location of nearest cover had better predictive value for the initial orientation of C. draconoides escapes than incline. On steep slopes (15 degrees), C. draconoides avoided running directly downhill and uphill and primarily ran horizontally, whereas on shallow slopes, lizards exhibited approximately equal amounts of horizontal, direct uphill, and direct downhill running.

The extent of variation in reptile field metabolism, and its causal bases, are poorly understood. We studied the energetics of the insectivorous lizard Callisaurus draconoides at a site in the California Desert (Desert Center) and at a site at the southern tip of the Baja Peninsula (Cabo San Lucas; hereafter, Cabo). Reproducing Callisaurus were smaller at Cabo than at Desert Center. The allometry of metabolism with body mass can account for most differences in whole-animal metabolism. There was no significant effect of sex or source population on mass-adjusted metabolic rate in the laboratory (resting metabolism, measured by closed-system respirometry) or in the field (field metabolism, measured with doubly labeled water). The mass-adjusted resting metabolism and field metabolism of gravid females and the field metabolism of juvenile lizards were not significantly different from those of nonreproductive adults. Temperature had a significant effect on resting metabolism (Q10 = 2.7); fed lizards had resting metabolism that was 22% higher than that of fasted lizards; field metabolism was positively correlated with growth rate in juveniles; and field metabolism of adults increased from spring to late summer at Desert Center by 25%, probably because of longer activity period length and slightly higher activity period body temperature. We calculated from water influx and field metabolism that juveniles allocated 18% of their metabolizable energy intake to growth and that most energy deposited into eggs was transferred from energy stores rather than ingested in the weeks prior to laying.