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At least 127 records · Page 7Linked to original sources
PubMed2001

Temperature cycles induce a bimodal activity pattern in ruin lizards: masking or clock-controlled event? A seasonal problem.

The daily locomotor activity pattern of Ruin lizards in the field is mainly unimodal, except for summer months when soil temperatures exceed 40 degrees C to 42 degrees C around midday. In such a situation, lizards reduce their locomotor activity around midday to avoid overheating, and thus their daily activity pattern becomes bimodal. The bimodal pattern expressed in the field is usually retained in the free-running rhythm under constant temperature and DD for a couple of weeks, after which the bimodal pattern changes into a unimodal pattern. In the present study, the authors examined whether 24-h temperature cycles (TCs) would change lizard activity from a unimodal to a bimodal pattern. Administration of TCs to unimodal lizards free-running in DD is able to entrain locomotor rhythms and to induce a bimodal pattern both in summer and autumn-winter. There are, however, striking seasonal differences in the effectiveness with which TCs achieve bimodality: (a) Numbers of lizards rendered bimodal are significantly higher in summer than in autumn-winter; (b) TCs require less time to achieve bimodality in summer than autumn-winter; (c) bimodality is retained as an aftereffect in the postentrainment free-run in summer, but not in autumn-winter; (d) TCs change activity duration in summer, but not in autumn-winter. All this demonstrates the existence of seasonal changes in responsiveness of the circadian oscillators controlling activity to the external factors inducing bimodality. Oscillators' responsiveness is high in summer, when bimodality is the survival strategy of Ruin lizards to avoid overheating around midday in open fields, and low in autumn-winter, when bimodality has no recognizable adaptive significance.

Activity Cycles↗
PubMedDate not supplied

Age related differences in lipophilic compounds found in femoral gland secretions of male spiny-footed lizards, Acanthodactylus erythrurus.

Although chemoreception plays an important role in social organization of many lizards, only a few studies have examined the chemicals found in secretions used for intraspecific communication. We report the composition of the secretion of the femoral glands of males of the spiny-footed lizard (Acanthodactylus erythrurus). On the basis of mass spectra, obtained by GC/MS, we identified 45 lipophilic compounds, including several alcohols ranging from 10 to 29 carbon atoms (mainly hexacosanol and tetracosanol), steroids (mainly cholesterol and dehydrocholesterol), n-C9 to n-C20 carboxylic acids, esters of carboxylic acids, and minor components such as lactones, ketones, squalene and a-tocopherol. Some of these compounds are reported for the first time in lizards. Adult and subadult males differed in the composition of secretions, with C9 to C15 carboxylic acids being more abundant in younger than in older lizards, whereas C16 to C20 carboxylic acids were more abundant in older lizards. Also, older lizards had significant lower proportions of cholesterol and campesterol but higher proportions of dehydrocholesterol.

Aging↗
PubMedDate not supplied

Lipids in the femoral gland secretions of male Schreiber's green lizards, Lacerta schreiberi.

In spite of the importance of chemoreception and chemical signals in social organization of lizards, only a few studies have examined the chemical composition of secretions that lizards use for intraspecific communication. The secretion of the femoral glands of male Schreiber's green lizards (Lacerta schreiberi) contains 51 lipophilic compounds, including several steroids, a-tocopherol, n-C9 to n-C22 carboxylic acids and their esteres, and minor components such as alcohols between C12 and C24, two lactones, two ketones, and squalene. These compounds were identified on the basis of mass spectra, obtained by GC-MS. We compared these chemicals with those found in other lizard species, and discussed how environmental conditions could explain the differential presence of chemicals in different lizards. Particularly, the high abundance of a-tocopherol in this lizard is suggested to contribute to avoid oxidation of other lipids in secretions, increasing chemical stability of scent marks in the humid conditions of its habitat.

Animals↗
PubMed2005

Effect of temperature on toxicity of a natural pyrethrin pesticide to green anole lizards (Anolis carolinensis).

Metabolic rates of reptiles vary with body temperature; therefore, the sensitivity of reptiles to a particular dose level of a pesticide might be expected to vary as well. The purpose of the present study was twofold: To evaluate the effects of temperature on the toxicity to green anole lizards (Anolis carolinensis) of a single concentration of a natural pyrethrin pesticide via percutaneous exposure, and to compare the effects of temperature (20 vs 35 degrees C) on the toxicity of different concentrations of pyrethrins to green anoles. When lizards were exposed to a solution that contained 300 mg/L of pyrethrins, the mortality of lizards maintained at 15 and 20 degrees C was significantly higher (p < 0.01) than the mortality of lizards maintained at 35 and 38 degrees C. In addition, the median lethal concentrations of pyrethrins for lizards maintained at 20 and 35 degrees C were 77.6 and greater than 300 mg/L, respectively. Therefore, temperature clearly influenced the sensitivity of lizards to pyrethrin pesticides.

Animals↗
PubMed1989

Dopamine antagonist speeds up tail regeneration in lizards exposed to continuous darkness: evidence for prolactin involvement.

In earlier studies, we demonstrated that continuous light (LL:LD, 24:0) stimulated tail regeneration whereas continuous darkness (DD:LD, 0:24) and pinealectomy depressed the same in the Gekkonid lizard, Hemidactylus flaviviridis, and, furthermore, exogenous prolactin significantly enhanced the regeneration process in lizards kept in 0:24 LD. However, the regeneration process in animals exposed to 24:0 LD was unaffected by the dopamine agonist, bromocriptine. This study with pimozide, an antipsychotic drug, and a potent dopamine receptor antagonist was conducted to ascertain whether the dopaminergic regulation of prolactin release is operative in lizards, as in mammals, and to provide further evidence for prolactin involvement in regenerative growth. Once daily intraperitoneal injection of 50 micrograms/kg pimozide to H. flaviviridis, 5 days prior to tail autotomy and 50 days thereafter, stimulated the regeneration process in lizards exposed to 0:24 LD. The initiation of regeneration, the total length of new growth (regenerate) produced by Day 50, and the total percentage replacement of the lost (autotomized) tails at the end of 50 days of experimentation were all significantly enhanced in pimozide-treated animals as compared with their counterparts injected with 0.6% sterile saline; in fact, better than saline-injected controls exposed to 24:0 LD of 638 lux intensity. The daily growth rate was also enhanced in pimozide-treated lizards. Interestingly, the pattern of regeneration as well as the final regenerate of pimozide-treated lizards were similar to those observed earlier in ovine prolactin-treated animals exposed to similar experimental photoperiodic schedules.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Susceptibility of the western fence lizard (Sceloporus occidentalis) to the Lyme borreliosis spirochete (Borrelia burgdorferi).

Attempts to infect juvenile and adult western fence lizards (Sceloporus occidentalis) with the Lyme borreliosis spirochete (Borrelia burgdorferi) were largely unsuccessful. Spirochetes could not be isolated from the blood and various tissues of 14 lizards 21-32 days after they had been inoculated ip (n = 8) or sc (n = 6) with 10(6) or 10(8) B. burgdorferi representing 3 tick isolates, although 1 lizard apparently developed a transitory spirochetemia lasting 2 days. Similarly, spirochetes could not be detected in the blood or tissues of 5 lizards fed upon by 2- greater than 8 infected larvae or nymphs of the western black-legged tick (Ixodes pacificus). Sixty-five blood samples from 59 lizards in an endemic area and various tissues from 20 of the same lizards were also assayed for B. burgdorferi with negative results. The implications of these findings for the maintenance of this spirochete in natural foci are discussed.

Animals↗
PubMed1992

Lesion and regeneration in the medial cerebral cortex of lizards.

The cerebral cortex of Squamate reptiles (lizards and snakes) may be regarded as an archicortex or "reptilian hippocampus". In lizards, one cortical area, the medial cortex, may be considered as a true "fascia dentata" on grounds of its anatomy, connectivity and cyto- chemo-architectonics of its main zinc-rich axonal projection. Moreover, its late ontogenesis and postnatal development support this view. In normal conditions, it shows delayed postnatal neurogenesis and growth during the lizard's life span. Remnant neuroblasts in the medial cortical ependyma of adult lizards seasonally proliferate. The late-produced immature neurocytes migrate to the medial cortex cell layer where they differentiate and give off zinc-containing axons directed to the rest of cortical areas. This results in a continuous growth of the medial cortex and its zinc-rich axonal projection. Perhaps the most important characteristic of the lizard medial cortex is that it can regenerate after having been almost completely destroyed. Recent experiments in our laboratory have shown that chemical lesion of its neurons (up to 95%) results in a cascade of events; first, those related with massive neuronal death and axonal-dendritic retraction and, secondly, those related with a triggered neuroblast proliferation and subsequent neo-histogenesis, and the regeneration of an almost new medial cortex that shows itself undistinguishable from a normal undamaged one. This is the only report to our knowledge that an amniote central nervous centre may regenerate by new neuron production and neo-histogenesis. Perhaps the medial cortex of lizards may be used as a model for neuronal regeneration and/or transplant experiments in mammals or even in primates.

Animals↗
PubMed1998

Borreliacidal factor in the blood of the western fence lizard (Sceloporus occidentalis).

In some populations of the western black-legged tick, Ixodes pacificus, the prevalence of infection with Lyme disease spirochetes (Borrelia burgdorferi) in nymphal ticks exceeds those in adult ticks by 3-4-fold. Experiments were conducted to determine if the reduced spirochetal prevalence in adult ticks is due to the presence of anti-borrelial antibodies or to another borreliacidal factor in the blood of the western fence lizard, Sceloporus occidentalis, a primary host of subadult I. pacificus, or to loss of spirochetes as nymphal ticks molt to the adult stage. Ten lizards were each exposed to the feeding activities of 10 nymphs having a 78% prevalence of B. burgdorferi infection. Five of the lizards had been hyperimmunized first with 10(8) heat-killed spirochetes and 5 were seronegative to B. burgdorferi. After repletion and the transstadial molt, none of 62 resultant adult ticks from both groups of lizards was found to contain spirochetes. In contrast, 11 of 20 (55%) infected nymphs that had fed on 4 preimmune rabbits passed spirochetes to adult ticks. Taken together, these findings demonstrate that host immunoglobulins and the transstadial molt by themselves are not necessary for eliminating B. burgdorferi from infected nymphal ticks. A novel in vitro assay revealed that nearly all spirochetes placed in plasma or sera from lizards died in less than 1 hr, whereas many spirochetes injected into mouse plasma or sera survived for 72 hr. When spirochetes were put in lizard sera that had been preheated (100 C for 10 min) and allowed to cool, survival was extended to 72 hr. We conclude that the blood of S. occidentalis contains a thermolabile, borreliacidal factor, probably a protein, that destroys spirochetes in the midgut diverticula of feeding I. pacificus nymphs.

Animals↗
PubMed1999

Effects of Protective Fencing on Birds, Lizards, and Black-Tailed Hares in the Western Mojave Desert.

/ Effects of protective fencing on birds, lizards, black-tailed hares (Lepus californicus), perennial plant cover, and structural diversity of perennial plants were evaluated from spring 1994 through winter 1995 at the Desert Tortoise Research Natural Area (DTNA), in the Mojave Desert, California. Abundance and species richness of birds were higher inside than outside the DTNA, and effects were larger during breeding than wintering seasons and during a high than a low rainfall year. Ash-throated flycatchers (Myiarchus cinerascens), cactus wrens (Campylorhynchus brunneicapillus), LeConte's thrashers (Toxostoma lecontei), loggerhead shrikes (Lanius ludovicianus), sage sparrows (Amphispiza belli), and verdins (Auriparus flaviceps) were more abundant inside than outside the DTNA. Nesting activity was also more frequent inside. Total abundance and species richness of lizards and individual abundances of western whiptail lizards (Cnemidophorous tigris) and desert spiny lizards (Sceloporus magister) were higher inside than outside. In contrast, abundance of black-tailed hares was lower inside. Structural diversity of the perennial plant community did not differ due to protection, but cover was 50% higher in protected areas. Black-tailed hares generally prefer areas of low perennial plant cover, which may explain why they were more abundant outside than inside the DTNA. Habitat structure may not affect bird and lizard communities as much as availability of food at this desert site, and the greater abundance and species richness of vertebrates inside than outside the DTNA may correlate with abundances of seeds and invertebrate prey. KEY WORDS: Birds; Fenced protection; Lepus californicus, Lizards; Mojave Desert; Off-highway vehicles; Protected area management; Sheep grazing

Journal Article↗
PubMed2000

Monogamy in lizards.

Monogamy is relatively rarely reported in taxa other than birds. The reproductive system of many lizard species appears to involve multiple mating partners for both the male and the female. However, short-term monogamous relationships have been reported in some lizard species, either where the male defends a territory that is only occupied by a single adult female, or where males stay with females for a period of time after mating, apparently to guard against rival males. There are a few reported cases of more prolonged monogamous relationships in lizards, with the Australian sleepy lizard, Tiliqua rugosa, the best studied example. Adult males and females of this species form monogamous pairs for an extended period before mating each spring, and they select the same partner in successive years. The paper reviews possible functions of monogamy in this and other lizard species, and suggests that the additional perspective from studying lizards may enrich our overall understanding of monogamous behaviour.

Journal Article↗
PubMed2003

Influence of predation pressure on the escape behaviour of Podarcis muralis lizards.

Relationships between predator avoidance behaviour and predation pressure were investigated in the wall lizard, Podarcis muralis. The wariness of lizards belonging to high (1185m) and low elevation (308m) populations under two different predation pressure levels was compared. Wall lizards belonging to the lowland population experienced greater predation pressure than those belonging to the highland population. Lizards belonging to the population under higher predation pressure had higher frequency of refuge use, and had longer flight initiation distances (i.e. the distance lizards allowed the observer to approach before fleeing). In contrast, neither the distance fled (i.e. the total distance they fled in one continuous movement from the lizard's initial position until hiding or stopping at a safe distance) nor the distance to the nearest refuge were significantly different between populations. Escape responses were independent of ambient temperature in the lowland population, but animals belonging to the highland population had longer flight initiation distances when the ambient temperatures were higher. These findings suggest that predator avoidance behaviour may vary with predation pressure.

Journal Article↗
PubMed2002

Testing amniote models of prey transport kinematics: a quantitative analysis of mouth opening patterns in lizards.

Two models have been proposed to describe the prey transport kinematics of terrestrial vertebrates (Bramble and Wake, 1985; Reilly and Lauder, 1990). The critical difference between the models is the presence or absence of a slow open-II phase (SO-II) in the gape profile during mouth opening. Each of these models has been applied to lizards, however to date, lizard feeding kinematics have not been adequately quantified to assess the utility of these models for this clade. Neither model has been sufficiently tested due to the lack of a methodology to assess the specific differences between the models. We describe a method that uses explicit mathematical criteria to define the kinematic phases in tetrapod feeding. This "slope analysis& is used to precisely quantify and compare the transport kinematics of seven lizard species. Lizard transport kinematics were highly variable both within and across taxa. However, several common gape cycle patterns were identified. The predominant patterns were slow-fast opening (37.3%), fast opening only (22.9%) and slow opening only (21.2%). The most common pattern explicitly fits the prediction of the Reilly and Lauder model while the other two are similar to patterns observed in salamanders. Thus, lizards possess both the slow opening-fast opening pattern predicted for amniotes and the more primitive, simple opening pattern characteristic of more basal tetrapods. Plateau phases were found in only 12.8% of the profiles and only a fourth of these (3.4% of the total) explicitly fit the Bramble and Wake model (slow opening, plateau, fast opening) and two species never exhibited plateaus in their gape cycles. Thus, it is clear that the Bramble and Wake model is not supported as a generalized model for lizards or generalized tetrapods.

Journal Article↗
PubMed1999

Comparative three-dimensional kinematics of the hindlimb for high-speed bipedal and quadrupedal locomotion of lizards

Although lizards have been model organisms for testing locomotor performance and in ecomorphological studies, the limb movements of lizards during high-speed locomotion are poorly understood. Thus, we quantified the three-dimensional kinematics of the hindlimb, body and tail for five morphologically distinct species of lizard during steady-speed locomotion near maximum sprinting speed (2-5 m s-1). The kinematics of different species had little multivariate overlap. More than half of the strides of all species had digitigrade foot posture, but the frequency of using digitigrade foot posture varied among species. The combination of digitigrade foot posture and large foot size of the lizards contributed substantially to the high values of hip height. For each species, different suites of kinematic variables distinguished bipedal from quadrupedal strides. Interspecific morphological variation did not correspond globally to variation in kinematics, although lizard species with elongated hindlimbs took longer strides than species with shorter hindlimbs. The Froude numbers and relative stride lengths of all lizards running near maximal speeds were large compared with those reported previously for other vertebrates.

Journal Article↗
PubMed1976

Parietal eye-pineal morphology in lizards and its physiological implications.

Pineal complexes in 85 species of lizards examined comprised seven morphological types. Members of the same family do not necessarily have the same pineal complex type. "Regressive" parietal eyes were not common except in certain arboreal lizards, primarily from the family Chameleontidae. The parietal eye is often retained in burrowing lizards, presumably because these animals are occasionally exposed to light and the parietal eye is a more suitable photoreceptor for a burrower than are lateral eyes. The pineal of certain lizards possesses a finger-like projection that extends toward the parietal eye. This extension, along with pineal wall convolutions, results in more photoreceptor cells oriented for maximal absorption of light. It is rare to find convolutions and an extension in the same pineal. Cartilage deposits and blood sinuses may modify the intensity and wavelength of light reaching the pineal. These observations suggest that the intracranial pineal of lizards is a more important photoreceptor than was previously realized, a situation that may be a factor in the occasional "failure" of parietalectomy experiments.

Animals↗
PubMed2005

Comparative functional analysis of the hyolingual anatomy in lacertid lizards.

The tongue is often considered a key innovation in the evolution of a terrestrial lifestyle as it allows animals to transport food items through the oral cavity in air, a medium with low density and viscosity. The tongue has been secondarily coopted for a wide diversity of functions, including prey capture, drinking, breathing, and defensive behaviors. Within basal lizard groups, the tongue is used primarily for the purpose of prey capture and transport. In more derived groups, however, the tongue appears specialized for chemoreceptive purposes. Here we examine the tongue structure and morphology in lacertid lizards, a group of lizards where the tongue is critical to both food transport and chemoreception. Because of the different mechanical demands imposed by these different functions, regional morphological specializations of the tongue are expected. All species of lacertid lizards examined here have relatively light tongue muscles, but a well developed hyobranchial musculature that may assist during food transport. The intrinsic musculature, including verticalis, transversalis, and longitudinalis groups, is well developed and may cause the tongue elongation and retraction observed during chemoreception and drinking. The papillary morphology is complex and shows clear differences between the tongue tips and anterior fore-tongue, and the more posterior parts of the tongue. Our data show a subdivision between the fore- and hind-tongue in both papillary structure and muscular anatomy likely allowing these animals to use their tongues effectively during both chemoreception and prey transport. Moreover, our data suggest the importance of hyobranchium movements during prey transport in lacertid lizards.

Animals↗
PubMed1995

NADPH diaphorase-positive neurons in the lizard hippocampus: a distinct subpopulation of GABAergic interneurons.

We analyzed the distribution and light-microscopic features of the NADPH diaphorase-containing structures in the lizard hippocampus, likely to correspond to nitric oxide synthase-containing cells and fibers, and thus likely to release nitric oxide. We also studied co-localization of NADPH diaphorase with the neurotransmitter GABA, the calcium-binding protein parvalbumin, and the neuropeptide somatostatin, in order to examine whether putative nitric oxide-synthesizing neurons represent a different subpopulation of GABA cells, on which the authors recently reported in lizards. We also studied co-localization of NADPH diaphorase with parvalbumin or somatostatin in mice to ascertain whether the characteristics of this population in reptiles parallel the situation in mammals. Most of the positive NADPH diaphorase neurons were stained in a Golgi-like manner and were in the plexiform layers of the lizard hippocampus with morphologies ranging from bipolar to multipolar. Co-localization with GABA was 100%, and NADPH diaphorase-positive neurons in the lizard hippocampus did not contain parvalbumin or somatostatin. The results indicate that putative nitric oxide-synthesizing neurons represent a distinct subpopulation of GABA interneurons in the lizard hippocampus. Two different types of fibers were described in the plexiform layers: one type bearing thick varicosities, and the other thinner ones. We discuss the possibility that at least part of the positive fibers arise from a hypothalamic aminergic nucleus contacting the third ventricle, the periventricular hypothalamic organ. Most radial glia were stained almost completely and formed typical end-feet both at the pia and around capillaries. The results of this study confirm that the capacity for synthesizing nitric oxide is linked to a determined set of neuronal markers depending on the specific brain region, and they provide new resemblances between hippocampal regions in different classes of vertebrates.

Animals↗
PubMed1995

External and internal influences on indices of physiological stress: II. Seasonal and size-related variations in blood composition in free-living lizards, Sceloporus occidentalis.

Seasonal changes in blood composition (plasma osmolality, total plasma protein, hematocrit) in two free-living populations of fence lizards, Sceloporus occidentalis, one living in a very arid environment (Pearblossom, CA) and another in a milder desert (Bend, OR), were analyzed. In this analysis, two features of reptilian physiology and ecology were incorporated: ontogenetic variation in blood composition and seasonal variation in body-size distribution. The population living in the arid environment, but not the mild environment, exhibited significant seasonal changes in blood composition: mean plasma osmolality increased (345 +/- 4 to 356 +/- 3 mOsmol/kg) and mean plasma protein (4.19 +/- 0.20 to 3.34 +/- 0.14 g/dl) and hematocrit decreased (43.8 +/- 0.3 to 31.6 +/- 0.4) from April to August. These changes suggested that the physiological condition of the California population was affected by seasonal changes in the external environment. However, among individuals, a significant portion of the variation in blood composition was associated with an internal factor, body size. Larger lizards had higher osmolality, total protein, and hematocrit than smaller lizards in all seasons. In addition, the mean body size of active lizards decreased from April to August in California, but not Oregon. Because the body-size distribution of active lizards in California shifted between seasons, changes in mean population values of these blood parameters probably do not accurately reflect changes that occur within individuals and therefore may be misleading in assessing the physiological consequences of drought.

Analysis of Variance↗
PubMed2005

Wound keratins in the regenerating epidermis of lizard suggest that the wound reaction is similar in the tail and limb.

The keratin cytoskeleton of the wound epidermis of lizard limb (which does not regenerate) and tail (which regenerates) hase been studied by qualitative ultrastructural, immunocytochemical, and immunoblotting methods. The process of re-epithelialization is much shorter in the tail than in the limb. In the latter, a massive tissue destruction of bones, and the shrinkage of the old skin over the stump surface, delay wound closure, maintain inflammation, reduce blastemal cell population, resulting in inhibition of regeneration. The expression of special wound keratins found in the newt epidermis (W6) or mammalian epidermis (K6, K16, and K17) is present in the epidermis of both tail and limb of the lizard. These keratins are not immunolocalized in the migrating epithelium or normal (resting) epidermis but only after it has formed the thick wound epithelium, made of lacunar cells. The latter are proliferating keratinocytes produced during the cyclical renewal or regeneration of lizard epidermis. W6-immunolabeled proteic bands mainly at 45-47 kDa are detected by immunoblotting in normal, regenerating, and scarring epidermis of the tail and limb. Immunolabeled proteic bands at 52, 62-67 kDa (with K6), at 44-47, 60, 65 kDa (with K16), and at 44-47 kDa (with K17) were detected in normal and regenerating epidermis. It is suggested that: (1) these keratins constitute normal epidermis, especially where the lacunar layer is still differentiating; (2) the wound epidermis is similar in the limb and tail in terms of morphology and keratin content; (3) the W6 antigen is similar to that of the newt, and is associated with tonofilaments; (4) lizard K6 and K17 have molecular weights similar to mammalian keratins; (5) K16 shows some isoforms or degradative products with different molecular weight from those of mammals; (6) K17 increases in wound keratinocytes and localizes over sparse filaments or small bundles of short filaments, not over tonofilaments joined to desmosomes; and (7) failure of limb regeneration in lizards may not depend on the wound reaction of keratinocytes.

Amputation Stumps↗