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At least 19 recordsLinked to original sources
PubMed1989

Is the pineal involved in the stimulatory influence of prolactin on tail regeneration in lizards? Studies with exogenous prolactin in lizards exposed to continuous darkness.

We have recently demonstrated that continuous light stimulates tail regeneration in the gekkonid lizard, Hemidactylus flaviviridis, whereas continuous darkness and pinealectomy depress regeneration. As a sequel to this observation, the effect of exogenous ovine prolactin (oPRL) on tail regeneration in normal (NL) and pinealectomized (PX) Hemidactylus exposed to continuous darkness (L:D 0:24) during the monsoon season was investigated. Once-daily intraperitoneal (ip) injections of 500 micrograms/kg oPRL were administered to a group of NL lizards, a group of PX lizards, and a group of sham-PX (sPX) lizards, 5 days prior to tail autotomy and 50 days afterward. Three groups--PX, sPX, and NL animals--served as the controls and received once-daily ip injections of 0.6% saline. Our observations show that initiation of regeneration, daily growth rate, total length of new growth (regenerate) at the end of regeneration, and total percentage replacement of lost (autotomized) tail were all significantly enhanced in oPRL-treated NL lizards as compared with their saline-treated (NL, PX, and sPX) and oPRL-treated (PX and sPX) counterparts. It is suggested that PRL may be the active factor that speeds up the rate of tail regeneration in lacertilians. The role of the pineal organ in vertebrate photoreception and the possibility that in Hemidactylus the presence of an intact pineal is somehow linked with the favorable influence of PRL on tail regeneration are discussed.

Animals↗
PubMed1985

Comparison of thermal acclimation effects on the metabolism of Chalcides ocellatus (desert lizard) and Lacerta vivipara (cool-temperate lizard).

The ocellated lizard, Chalcides ocellatus, and the common lizard, Lacerta vivipara, were acclimated to two temperature regimes (10 and 30 degrees C with 12L:12D photoperiod) for 2 weeks. The oxygen consumption rates were measured for both species at temperatures between 5 and 35 degrees C. Cold acclimation was observed in L. vivipara and was in the form of an upward translation of the metabolic rate-temperature curve in comparison to the warm-acclimated lizards (30 degrees C). Chalcides ocellatus showed a response to cold acclimation by decreasing its metabolism only at 10 degrees C.

Acclimatization↗
PubMed1985

Extraretinal photoreception in the lizard Sceloporus occidentalis: phase response curve.

All submammalian vertebrates have extraretinal photoreceptors (ERR) that can mediate entrainment of circadian rhythms to 24-h light-dark (LD) cycles. Phase response curves (PRC) for 6-h fluorescent light pulses were generated for lizards (Sceloporus occidentalis) previously subjected to sectioning of both optic nerves (ONX). The PRC for ONX lizards (only ERRs present) shows a threefold increase in the amplitude of both the advance and delay portions of the PRC compared with a PRC previously generated for sighted S. occidentalis. Also, in contrast to sighted lizards the area of the advance part of the PRC of ONX lizards is greater than the delay portion. Consistent with the shape of the respective PRCs in ONX vs. sighted lizards are the following facts. 1) The range of entrainment to LD cycles is greater in ONX lizards; some sighted lizards free-ran when exposed to LD 6:21.5 or LD 6:23.5 but entrained after ONX lizards reentrained to an 8-h shift in the phase of a LD 6:18 cycle significantly faster than sighted lizards. 3) Forty-two percent of ONX lizards showed a shorter free-running period (tau) in LL than DD, whereas 90% of sighted lizards showed a longer free-running period in LL than in DD. In those lizards in which tau LL greater than tau DD, the the average tau change in ONX lizards in was significantly less than that observed in sighted lizards. These results are consistent with the hypothesis that the eyes have an "inhibitory" role in the circadian system of S. occidentalis.

Animals↗
PubMed1991

Interactive effects of thyroxine and experimental location on running endurance, tissue masses, and enzyme activities in captive versus field-active lizards (Sceloporus undulatus).

This study investigates the effects of exogenous thyroxine (T4) on running endurance, tissue masses, and the activities of citrate synthase (CS), pyruvate kinase (PK), cytosolic alpha-glycerophosphate dehydrogenase (alpha-GPDH), and beta-hydroxyacyl Coenzyme A dehydrogenase (HOAD) in Sceloporus undulatus (eastern fence lizard). The enzymes were assayed to indicate maximal catabolic activities that support exercise. Parallel experiments were done on captive and field-active groups to determine whether responses in captive studies adequately predict responses in nature. Exogenous T4 was administered via intraperitoneal pellets. The effect of T4 on running endurance was dependent on the location of the experiment (P = 0.040) such that stamina was increased by T4 only in field-active lizards. At lower levels of biological organization, interactivity between T4 and experimental location was evident but less prevalent than at the level of the whole animal, and some location effects occurred independent of T4 treatment. Heart and kidney masses were significantly greater and total hind leg muscle mass was less in captive than in field-active lizards. Thyroxine reduced liver mass in both locations and kidney mass only in captive lizards. Mass-specific CS and alpha-GPDH in gastrocnemius muscle (mixed fiber type) and HOAD in heart were lower in captive than in field-active lizards; PK in heart and liver and alpha-GPDH in heart were higher in captive lizards. Thyroxine increased CS in liver and HOAD in heart, decreased alpha-GPDH in liver in both locations, and decreased alpha-GPDH in gastrocnemius only in captive lizards. The effects of T4 differed significantly between experimental locations in gastrocnemius muscle (T4 decreased PK only in captive lizards) and in liver (T4 increased PK in field-active lizards and decreased PK in captive lizards). The mechanistic basis of differences in stamina between captive and field-active and between placebo and T4-treated lizards is largely unexplained by the factors measured here, thus illustrating the uncertainty of predicting organismal performance from lower level measurements. Nonetheless, T4 has now been shown to have greater physiological activity in field-active than in captive Sceloporus with regard to resting and total daily metabolic rates and running endurance. The results of this study further confirm that endocrine experiments on captive animals may not predict responses in nature. Further efforts to clarify the physiological significance of seasonal variations in levels of thyroid hormones will have to involve, at least in part, invasive studies on field-active lizards.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1990

Virulence of lizard malaria: the evolutionary ecology of an ancient parasite-host association.

The negative consequences of parasitic infection (virulence) were examined for two lizard malaria parasite-host associations: Plasmodium agamae and P. giganteum, parasites of the rainbow lizard, Agama agama, in Sierra Leone, West Africa; and P. mexicanum in the western fence lizard, Sceloporus occidentalis, in northern California. These malaria species vary greatly in their reproductive characteristics: P. agamae produces only 8 merozoites per schizont, P. giganteum yields over 100, and P. mexicanum an intermediate number. All three parasites appear to have had an ancient association with their host. In fence lizards, infection with malaria is associated with increased numbers of immature erythrocytes, decreased haemoglobin levels, decreased maximal oxygen consumption, and decreased running stamina. Not affected were numbers of erythrocytes, resting metabolic rate, and sprint running speed which is supported by anaerobic means in lizards. Infected male fence lizards had smaller testes, stored less fat in preparation for winter dormancy, were more often socially submissive and, unexpectedly, were more extravagantly coloured on the ventral surface (a sexually dimorphic trait) than non-infected males. Females also stored less fat and produced smaller clutches of eggs, a directly observed reduction in fitness. Infected fence lizards do not develop behavioural fevers. P. mexicanum appears to have broad thermal buffering abilities and thermal tolerance; the parasite's population growth was unaffected by experimental alterations in the lizard's body temperature. The data are less complete for A. agama, but infected lizards suffered similar haematological and physiological effects. Infected animals may be socially submissive because they appear to gather less insect prey, possibly a result of being forced into inferior territories. Infection does not reduce clutch size in rainbow lizards, but may lengthen the time between clutches. These results are compared with predictions emerging from several models of the evolution of parasite virulence. The lack of behavioural fevers in fence lizards may represent a physiological constraint by the lizards in evolving a thermal tolerance large enough to allow elimination of the parasite via fever. Such constraints may be important in determining the outcome of parasite-host coevolution. Some theory predicts low virulence in old parasite-host systems and higher virulence in parasites with greater reproductive output. However, in conflict with this argument, all three malarial species exhibited similar high costs to their hosts.

Animals↗
PubMed1992

The western fence lizard Sceloporus occidentalis: evidence of field exposure to Borrelia burgdorferi in relation to infestation by Ixodes pacificus (Acari: Ixodidae).

The role of the Western fence lizard Sceloporus occidentalis in the enzootiology of the Lyme disease spirochete Borrelia burgdorferi was evaluated in the Hopland and Ukiah areas of Mendocino County, California. In 1989, half of 74 lizards collected monthly from April to October at Hopland were infested by the immature western black-legged tick Ixodes pacificus at a mean intensity of 6.0 ticks per lizard. The prevalence of infestation of lizards by immature I. pacificus (36 of 73) at Ukiah was similar, but the mean intensity (12.9) was approximately twice as great. Overall, zero of 223 larvae and 2 (0.6%) of 330 nymphs from both sites were found to contain spirochetes by direct immunofluorescence. Larval and nymphal I. pacificus fit the negative binomial distribution in spring, and the prevalence and abundance of these stages were significantly greater in spring than in summer at both sites. Spirochetes were not visualized in thick blood films prepared from 133 lizards from both localities. Plasma antibodies against B. burgdorferi were detected in seven of 10 experimentally inoculated lizards, in five (8%) of 63 lizards from Hopland, and in 10 (14%) of 70 lizards from Ukiah. Adult lizards had a significantly greater tick burden and seropositivity rate than juvenile lizards only at Ukiah. In 1991, efforts to detect and culture spirochetes from the blood of 21 wild-caught lizards and from the tissues of 189 associated ticks that fed xenodiagnostically on them were unsuccessful.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1990

Thyroid regulation of resting metabolic rate and intermediary metabolic enzymes in a lizard (Sceloporus occidentalis).

This study investigates the effects of physiological increments in plasma thyroxine (T4) at three levels of biological organization in thyroid-intact and thyroidectomized captive western fence lizards, Sceloporus occidentalis. Two doses of T4-loaded pellets elevated plasma T4 in thyroid-intact lizards from 4.8 +/- 0.47 to 10.7 +/- 2.25 and 20.4 +/- 5.77 ng/ml (mean +/- SE). Surgical thyroidectomy reduced T4 to 1.8 +/- 0.23 ng/ml, and subsequent T4 pellet implantation raised T4 to 14.8 +/- 4.30 ng/ml. Minimal resting metabolic rate (= standard metabolic rate; SMR), a common organismal metric of thyroid perturbation, was reduced 31% (P less than 0.0001) by thyroidectomy and was restored by T4 replacement but was not stimulated by T4 supplementation in thyroid-intact lizards. In T4-replaced, thyroidectomized lizards, SMR was significantly correlated with plasma T4 (r2 = 0.626, P = 0.003, n = 11). At the organ level, liver mass was not changed by any treatment; heart mass was decreased by thyroid deficiency and restored by T4 replacement. At the molecular level, citrate synthase activity was significantly reduced by thyroidectomy and was returned to control levels by T4 replacement in liver and skeletal muscle (gastrocnemius) but was not changed in cardiac muscle. Citrate synthase was not affected in any tissue by T4 supplementation in thyroid-intact lizards. Pyruvate kinase activity was not affected by any of the treatments in any of the tissues. Cytosolic alpha-glycerophosphate dehydrogenase was significantly reduced in liver by all treatments and in skeletal muscle by T4 replacement after thyroidectomy. These results indicate that SMR and cardiac muscle mass in lizards are dependent on normal thyroid function and are expressed maximally in euthyroid animals. The stimulatory effect of T4 on SMR in thyroid-intact lizards, which has been reported previously by several investigators, is a nonphysiological response to pharmacological T4 levels, at least in these captive lizards. Molecular responses are tissue and enzyme dependent and cannot be generalized. Pellet implantation is an effective means of inducing physiological increments in plasma T4 and should replace previously used injection protocols. This new method can be used in capture-recapture experiments involving field-active lizards.

Animals↗
PubMed1990

Saurian malaria in Kenya: epidemiological features of malarial infections in lizard populations of the West Pokot District.

During investigations into the prevalence of malarial parasites among lizards in the West Pokot District in Kenya, 179 lizards comprising eight species were caught. Examination of the Giemsa-stained smears made from their blood showed that 34 lizards were infected with Plasmodium species. Fifteen lizards were infected with a single species of Plasmodium and 19 carried multiple infections, the maximum, in four lizards, was four species. There were 19 combinations of parasite infections. Seventeen Plasmodium species were identified, the commonest being P. icipeensis. Only two of the eight lizard species were infected: the skink Mabuya striata and the agamid Agama agama. Eight of the Plasmodium species infected both; another eight species infected M. striata only but three of these have been described from different lizard families elsewhere in Africa. P. robinsoni infected A. agama only, although it was first described from another lizard family in another part of Africa. The epidemiological significance of these results is discussed.

Animals↗
PubMed1985

Age-related differences in the response of hepatic oxygen consumption to thermal stress in the male garden lizard.

The main aim of the present study is to compare the thermal adaptation capacity of young, middle-aged and old lizards with respect to hepatic oxygen consumption. Cold exposure (1 h at 0-4 degrees C) caused a decline in endogenous oxygen consumption in young but did not evoke significant changes in middle-aged and old lizards. On the other hand, with 5 mM succinate the rate of respiration increased marginally only in cold-exposed old lizards. This suggests that the metabolic response to cold is age-dependent in these lizards. Exposure of homogenates at 40 +/- 1 degree C for 15 min led to a rise in the hepatic oxygen consumption of young but not in that of either middle-aged or old lizards. There were no changes in the rate of oxygen consumption upon exposure for a similar period at 45 +/- 1 degree C of liver homogenates from lizards of three different age groups. However, exposure at 51 +/- 1 degree C resulted in a higher degree of decline in the rate of hepatic oxygen consumption in middle-aged and old than in young lizards. Thus, the young lizards appear to be better-adapted to hyperthermic stress than the middle-aged and old.

Adaptation, Physiological↗
PubMed1985

Distribution and ontogeny of B cells in the garden lizard, Calotes versicolor.

Surface immunoglobulin bearing (sIg+) cells were identified in the lizard Calotes versicolor by immunofluorescence using a polyvalent antiserum to lizard immunoglobulins and class-specific antibodies to lizard IgM and IgY. 53.3 +/- 1.6% of spleen cells, 23.6 +/- 0.8% of peripheral blood mononuclear cells, 21.5 +/- 1.8% of bone marrow mononuclear cells and less than 1% of thymus cells were found to bear immunoglobulin (Ig) on their surface. A similar proportion of cells in each tissue was stained with rabbit anti-lizard mu (specific for IgM) whereas only a small proportion of cells were stained with rabbit anti-lizard (specific for IgY). Adult thymectomy significantly increased the proportion of sIgM+ cells in spleen and blood whereas high dose cyclophosphamide (300mg/kg body weight) decreased the proportion of sIgM+ cells thus suggesting that sIg+ cells in the lizard are of B cell lineage as in higher vertebrates. Ontogenetic studies indicate that embryonic liver is an organ enriched for sIgM+ cells at certain stages of development and thus suggest liver to be a site for differentiation of sIg+ cells in lizard embryos.

Animals↗
PubMed1988

The role of aldosterone in water and electrolyte transport across the colonic epithelium of the lizard, Gallotia galloti.

1. The effects of D-aldosterone on the electrical properties and ionic transport have been analysed (in vitro) in the colonic epithelium of the lizard, Gallotia galloti. 2. The injection of 30 g of D-aldosterone induced a significant rise of plasma aldosterone concentration, sustained for 4 hr after administration. 3. Intraperitoneal injections of D-aldosterone caused a slight reduction of transmural potential difference (PD) and short-circuit current (Isc). 4. Net absorption of Na+ across the colon from aldosterone-treated lizards did not increase when compared to colon from normal lizards. Cl- absorption was increased in treated lizards. 5. Addition of mucosal barium to treated tissues brought about a sustained increase of PD and Isc. 6. The absorption of fluid in normal lizards was reversed to fluid secretion in treated lizards. 7. The effects of D-aldosterone on lizard colon are compared with those reported for the colon of mammals and birds.

Aldosterone↗
PubMed1989

Lyme disease in California: interrelationship of Ixodes pacificus (Acari: Ixodidae), the western fence lizard (Sceloporus occidentalis), and Borrelia burgdorferi.

The relationship of immature western black-legged ticks, Ixodes pacificus Cooley and Kohls, to the western fence lizard, Sceloporus occidentalis Baird and Girard, and to the Lyme disease spirochete, Borrelia burgdorferi, was investigated in chaparral and woodland-grass habitats in northern California from 1984 to 1986. Immature ticks were found on lizards in spring and summer, but the prevalence and abundance of ticks on this host were considerably greater in spring. The peak of larval abundance preceded that of nymphs by several weeks, but there was considerable seasonal overlap between these parasitic stages. Larvae and nymphs attached primarily to the lateral nuchal pockets of lizards in chaparral (99.5%) and woodland-grass (91.8%). The numbers of larvae infesting lizards in spring fit the negative binomial distribution in woodland-grass but not in chaparral; insufficient data precluded similar analyses for nymphs. Tick loads did not differ significantly with respect to age or gender of the lizard. Spirochetal infection rates (range, 0-3.7%) in I. pacificus immatures were comparable in both habitats and were similar to those reported previously for adults of this tick. Overall, 1 (0.9%) of 117 larvae and 10 (1.8%) of 552 nymphs were infected with spirochetes resembling B. burgdorferi. Spirochetes were not observed in blood smears prepared from 261 wild-caught lizards, including five lizards fed upon by infected ticks at the time of collection. These and other findings suggest that S. occidentalis, although an important host of I. pacificus immatures, may be less important as a source for infecting ticks with B. burgdorferi.

Animals↗
PubMed2026

Chromosome-Level Reference Genome of the Desert Night Lizard Xantusia vigilis.

We present a reference-quality genome assembly for the desert night lizard (Xantusia vigilis). The night lizards (Xantusiidae) are a family of small-bodied lizards found in North America (Xantusia), Central America (Lepidophyma), and Cuba (Cricosaura). The night lizard family has an independent evolutionary history of at least 80 million years from its sister taxa within Scincoidea. The Xantusiids have several unique ecological, behavioral and evolutionary characteristics. For instance, the family contains the only squamate species that form diploid, unisexual, parthenogenic lineages. In addition, most night lizards are viviparous and form stable kin groups that are maintained over multiple years, an unusual life history strategy among lizards. Combining PacBio long-read sequencing, Hi-C, and RNAseq data we developed a reference-quality genome for the desert night lizard, X. vigilis. We assembled a complete mitochondrion and ~ 2.2 Gb nuclear genome, with 20 scaffolds that correlate in size to the X. vigilis karyotype. In addition, we found that X. vigilis chromosome 1 aligns with gene content of both of macrochromosome 1 and microchromosome 9 from a genome assembly of a species in the sister family Cordylidae (Hemicordylus capensis).

Xantusia↗