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PubMed1997

3-Acetylpyridine-induced degeneration and regeneration in the adult lizard brain: a qualitative and quantitative analysis.

The neurotoxin 3-acetylpyridine (3AP) produces highly selective neuronal damage in specific areas of the lizard brain. Following 3AP intoxication, proliferation and migration of replacement neurons born in the ventricular walls lead to regeneration of the lesioned areas. Earlier studies established the time course of 3AP-induced degeneration and subsequent regeneration in the medial cerebral cortex of adult lizards (Font, E., García-Verdugo, J.M., Alcántara, S. and Lopez-García, C., Neuron regeneration reverses 3-acetylpyridine-induced cell loss in the cerebral cortex of adult lizards, Brain Res., 551 (1991) 230-235 [13]). Complementary to our previous studies, we now provide a qualitative and quantitative account of the extent and distribution of neurotoxic damage in the brain as a whole of lizards treated with 3AP using Nissl and Golgi stains, a degeneration-sensitive reduced-silver method, and electron microscopy. Additionally, [3H]thymidine autoradiography was used to assess changes in the rate of neurogenesis caused by the 3AP treatment. Single doses of 3AP caused degenerative changes in all the cortical areas, anterior dorsal ventricular ridge, deep layers of the lateral cortex, lateral amygdaloid nucleus, and nucleus sphericus, while sparing other brain areas. The most frequent neuropathic change after 3AP treatment was clumping of the nuclear chromatin with formation of pyknotic nuclei. Occasionally, a second type of injury was observed in neurons of the cell layer of the dorsomedial cortex (DMC). 3AP also caused a conspicuous loss of dendritic spines in bipyramidal neurons of the dorsomedial and dorsal cortices possibly representing transneuronal degeneration. Numbers of [3H]thymidine-labeled cells were higher in lizards previously treated with 3AP than in controls. These results demonstrate that the neurotoxic lesion is capable of inducing an increase in the normal rate of adult neurogenesis. Whereas regeneration in the remaining areas was morphologically and histologically complete, in some animals, cell proliferation in the DMC resulted in formation of an abnormal cell plate.

Animals↗
PubMed2003

Cloning of complimentary deoxyribonucleic acid encoding follicle-stimulating hormone and luteinizing hormone beta subunit precursor molecules in Reeves's turtle (Geoclemys reevesii) and Japanese grass lizard (Takydromus tachydromoides).

Reptilia is the only vertebrate class in which cDNA for the gonadotropin beta subunit precursor molecule has not been cloned. We have isolated the full-length cDNA clone encoding the LH beta subunit precursor molecule and a partial cDNA clone encoding the FSH beta subunit precursor molecule from a pituitary cDNA library of Reeves's turtle. We further clarified the nucleotide sequence of the remaining part of the turtle FSH beta cDNA and that of full-length cDNA encoding the LH beta subunit precursor molecule of the Japanese grass lizard, by means of the 5' rapid amplification of cDNA end (RACE) and 3' RACE. The nucleotide sequence of the turtle FSH beta cDNA we determined was 584 bp long and contained the coding sequence, 5' untranslated region (UTR) and 3' UTR of 396, 34, and 154 bp, respectively. The nucleotide sequence of the turtle LH beta we isolated was 498 bp long and contained the coding sequence, 5' UTR and 3' UTR of 420, 7, and 71 bp, respectively. The nucleotide sequence of the lizard LH beta we determined was 537 bp long and contained the coding sequence, 5' UTR and 3' UTR of 441, 35, and 61 bp, respectively. Amino acid sequences deduced from coding regions of the turtle FSH beta, LH beta and the lizard LH beta were 131, 139, and 146 residues, respectively. Referring to the amino acid sequences of the bullfrog FSH and LH beta subunit molecules determined chemically, we deduced the amino acid sequences of mature peptide. Amino acid sequences of mature peptides of the turtle FSH, turtle LH, and the lizard LH were 111, 112, and 112 residues, respectively. Amino acid sequences of the mature peptides were compared with those of other vertebrates. The amino acid sequence of the turtle FSH beta subunit molecule was 84.7-85.6, 67.8-71.4, and 61.3-62.2% identical to the FSH sequence of birds, mammals, and amphibians, respectively. The amino acid sequence of the turtle LH beta subunit molecule was 51.6-54.6, 36.2-48.7, and 56.3-57.5% identical to the LH sequence of birds, mammals, and amphibians, respectively. The amino acid sequence of the lizard LH beta subunit molecule was 39.1-47.1, 32.9-43.0, and 46.0-47.3% identical to the LH sequence of birds, mammals, and amphibians, respectively. These identity values suggest that the turtle or reptilian FSH beta subunit molecule is more closely related to avian and mammalian FSH beta subunit molecules than to amphibian FSH beta subunit molecules but reptilian LH beta subunit molecules are more closely related to amphibian LH beta subunit molecules than to avian and mammalian LH beta subunit molecules. This discrepancy in the molecular similarity relationship found in the reptilian FSH and LH beta subunit molecules can be interpreted by assuming that evolution speed was not the same among hormone species and also among vertebrate groups.

Amino Acid Sequence↗
PubMed2003

Beta-endorphin disrupts seasonal and FSH-induced ovarian recrudescence in the lizard Mabuya carinata.

Administration (ip) of an opioid peptide, beta-endorphin (beta-EP) (0.1, 0.5, or 1 microg beta-EP/day/lizard for 30 days) during seasonal recrudescence phase of the ovarian cycle inhibited ovarian recrudescence as shown by the absence of vitellogenic follicles in the ovary in contrast to their presence in treatment controls in the lizard Mabuya carinata. In the germinal bed, treatment of 0.1 microg beta-EP did not affect primordial follicles, whereas their mean number was significantly lower in lizards treated with 0.5 or 1 microg beta-EP compared to those of treatment controls. There was also suppression of oviductal development as shown by a significantly lower relative weight of the oviduct and regressed oviductal glands in lizards treated with all the dosages of beta-EP compared to treatment controls. In another experiment, administration of FSH (10 IU FSH/alternate day/lizard for 30 days) during the regression phase of the ovarian cycle induced development of vitellogenic follicles, whereas the treatment controls showed only previtellogenic follicles. In addition, there was a significant increase in the ovarian and oviductal weights compared to initial and treatment controls. However, simultaneous administration of similar dosage of FSH and beta-EP (0.5 microg/day/lizard) did not induce ovarian recrudescence as shown by the absence of vitellogenic follicles in the ovary and significantly lower weight of the ovary and the oviduct and the mean number of oogonia, oocytes, and primordial follicles compared to those of FSH-treated lizards. The results indicate that beta-EP inhibits seasonal as well as FSH-induced ovarian recrudescence. Inhibitory effect of beta-EP on follicular development despite FSH administration implies its effect at the ovarian level in M. carinata. While adversely affecting the ovarian follicular development, beta-EP did not affect the adrenal gland as there was no significant variation in the mean nuclear diameter of the adrenocortical cells of treatment controls and beta-EP-treated lizards. Furthermore, administration of beta-EP caused a significant decrease in the mean number of islands of white pulp of the spleen indicating its adverse effect on immunity.

Adrenal Glands↗
PubMed2002

Lizard reproductive medicine and surgery.

Lizards are a diverse group of some 4470 species, a wide variety of which are now kept in captivity. Interest in captive lizards continues to increase, wild populations seem to be declining in some areas, and herpetoculturists continue to succeed in breeding more species; consequently, veterinarians must understand basic lizard reproductive biology to successfully treat lizard patients with reproductive problems. Just obtaining First Filial Generation (F1) offspring is an accomplishment. But we must look down the road to maintain a species in captivity for succeeding generations, and a lineage may not continue if attention is not given to details of appropriate husbandry and proper reproductive pursuits. One study documents the senescence of lineages in parthenogenetic lizards in captivity apparently associated with husbandry problems [99].

Animals↗
PubMed1999

Pre-existing bacterial infections, not stress fever, influenced previous studies which labeled Gerrhosaurus major an afebrile lizard species.

Early studies indicated that the Sudan plated lizard, Gerrhosaurus major, did not exhibit a febrile response when challenged with bacterial pyrogen. More recent results indicated that a 14-day antibiotic treatment regime produced a significant decrease (0.5 +/- 0.1 degree C) in the mean selected body temperature (MSBT) for this species (31.3 +/- 0.2-30.8 +/- 0.2 degrees C). The antibiotic treatment results suggested that G. major already had a fever caused by a pre-existing bacterial infection. The current study was designed first to determine if a sub-population of G. major, with a higher mean pre-antibiotic treatment MSBT would exhibit a greater decrease in MSBT after antibiotic treatment. A 14-day antibiotic treatment regime for G. major (N = 7) with MSBTs > or = 31.9 degrees C (mean 32.4 +/- 0.2 degrees C) produced a significant decrease of 1.7 +/- 0.4 degrees C in MSBT to 30.7 +/- 0.3 degrees C. Analysis of the combined antibiotic treatment MSBT data from [13] and the current study demonstrated that the magnitude of the change in MSBT after antibiotic treatment was dependent upon the pre-antibiotic treatment MSBT. These data imply that animals with a greater pre-treatment MSBT and greater MSBT change had a greater magnitude fever. In the second portion of this study the MSBT for individual lizards was measured during separate experiments using both indwelling cloacal thermocouples taped to the tail of the lizard and telemeters implanted into the peritoneal cavity of the lizard. This second study was designed to determine if measurement of Tb using thermocouples induced a stress fever which may have masked a portion of the pyrogen-induced fever. The MSBT measured using indwelling cloacal thermocouples (30.5 +/- 0.3 degrees C) was not significantly greater (T > 0.05) than the MSBT increased using telemeters (31.0 +/- 0.2 degrees C). The results of the experiments from this study demonstrate that the previously reported afebrile state for G. major was the result of animals having pre-existing bacterial infections. G. major does exhibit a febrile response similar to other lizard species.

Animals↗
PubMedDate not supplied

Electrophysiological evidence for transient topographic organization of retinotectal projections during optic nerve regeneration in the lizard, Ctenophorus ornatus.

In the lizard, Ctenophorus ornatus, anatomical studies have revealed that optic axons regenerate to visual centers within 2 months of nerve crush but that, from the outset, the regenerated projections lack topographic order (Beazley et al., 1997; Dunlop et al., 1997b). Here we assess the functional topography of the regenerated retinotectal projections by electrophysiological recording of extracellular multiunit responses to visual stimulation and by observing the lizards' ability to capture live prey. At the completion of the electrophysiology, DiI was applied locally to the retina and the topography of the tectal projection later assessed. Electrophysiology revealed that, at 2-4.2 months, responses were weak and habituated readily; no retinotopic order was detected. Between 4.5-6 months, responses were more reliable and the majority of lizards displayed a crude retinotopic order, especially in the ventro-temporal to dorso-nasal retinal axis. Although responses were variable between 6-9 months, they tended to be more reliable again thereafter. However, from 6-18 months, the projection consistently lacked topography with many retinal regions projecting to each tectal locus. Lizards, including those with electrophysiological evidence of crude retinotopy, were consistently unable to capture live prey using the experimental eye. Labelling with DiI confirmed the absence of anatomical retinotopy throughout. Taken together, the electrophysiological and anatomical data indicate that retinotopically appropriate axon terminals (or parts thereof) are transiently active whilst inappropriately located ones are silent. Presumably in lizard map-making cues fade with time and/or the mechanisms are lacking to stabilize and refine the ephemeral map. Moreover, the transient retinotopy is insufficient for useful visual function.

Animals↗
PubMed2002

Parasitism of lizards by immature stages of the blacklegged tick, Ixodes scapularis (Acari, Ixodidae).

From 1982-1985 and 1993-1999, a total of 309 individual reptiles, mostly lizards and snakes, belonging to 12 species (American alligator, six lizard species, five snake species) was captured on St. Catherine's Island, Liberty County, Georgia, USA, and examined for ticks. Three lizard species, the broad-headed skink Eumeces laticeps, southeastern 5-lined skink Eumeces inexpectatus, and eastern glass lizard Ophisaurus ventralis, were severely infested with larvae and nymphs of the blacklegged tick, Ixodes scapularis. Ticks were not found on any of the other reptile species. Overall, 80% of 65 E. inexpectatus examined were parasitized by a mean intensity of 21.5 larvae and 88% were parasitized by a mean intensity of 4.8 nymphs. Corresponding figures for E. laticeps (n=56) were 93% and 51.3 for larvae and 89% and 7.4 for nymphs, and for O. ventralis (n=3) were 67% and 22.5 for larvae and 100% and 21.3 for nymphs. Larvae and nymphs attached along the lateral grooves of O. ventralis. Nymphs attached mainly behind the ears and in the foreleg axillae whereas larvae mainly attached to these sites and on the hindlegs in Eumeces spp. Seasonally, both larvae and nymphs were recorded on lizards from April through October. A unimodal larval peak was recorded in May or June. Seasonal data for nymphs did not reveal any distinct peaks but small bimodal peaks in mean intensities may have occurred (one in early summer, the other in late summer) suggesting that some ticks complete their life cycle in one year, and others in two years, on St. Catherine's Island. Potential epidemiological consequences of these findings with respect to Lyme disease in the southeastern United States are briefly addressed.

Animals↗
PubMed2003

Stimulus control of predatory behavior by the Iberian wall lizard (Podarcis hispanica, Sauria, Lacertidae): effects of familiarity with prey.

The authors examine the relative roles of vision and chemoreception and the influence of previous experience with prey on the predatory behavior of Iberian wall lizards (Podarcis hispanica). Experiment 1 compared the responses to visual, chemical, and a combination of visual and chemical cues of a familiar prey by 2 groups of lizards that had been kept in captivity for either 3 months or 21 days. Experiment 2 assessed the responses of lizards kept in the laboratory for more than 3 months to a novel prey species. The results reveal that feeding on a prey species affects the lizards' responses to chemical stimuli from that prey. The response to chemical cues of a novel prey requires a 1st-feeding experience with that prey. Lizards that have been fed the same prey species for several months cease responding to the chemical stimuli of that particular prey.

Animals↗
PubMed2004

The relationship between morphology, escape behaviour and microhabitat occupation in the lizard clade Liolaemus (Iguanidae: Tropidurinae: Liolaemini).

Phenotypic differences among species are known to have functional consequences that in turn allow species to use different habitats. However, the role of behaviour in this ecomorphological paradigm is not well defined. We investigated the relationship between morphology, ecology and escape behaviour among 25 species of the lizard clade Liolaemus in a phylogenetic framework. We demonstrate that the relationship between morphology and characteristics of habitat structure shows little or no association, consistent with a previous study on this group. However, a significant relationship was found between morphology and escape behaviour with the distance a lizard moved from a potential predator correlated with body width, axilla-groin length, and pelvis width. A significant relationship between escape behaviour and habitat structure occupation was found; lizards that occupied tree trunks and open ground ran longer distances from predators and were found greater distances from shelter. Behavioural strategies used by these lizards in open habitats appear to have made unnecessary the evolution of limb morphology that has occurred in other lizards from other clades that are found in open settings. Understanding differences in patterns of ecomorphological relationships among clades is an important component for studying adaptive diversification.

Analysis of Variance↗
PubMed1999

Seasonal variations in serotonin immunoreactivity and ultrastructure in the pineal organ of the Japanese grass lizard, with special reference to environmental temperature.

The seasonal variations in serotonin immunoreactivity and ultrastructure of the secretory rudimentary photoreceptor cells (SRPC) were studied in the pineal organ of the Japanese grass lizard, Takydromus tachydromoides in relation to the environmental temperature. Our results clearly demonstrated that serotonin immunoreactivity in the lizard pineal organ displayed seasonal variations under an artificial photoperiod of LD 12:12 and natural temperature in the laboratory. Immunoreactivity became intense with increase in temperature from spring to summer, showing the strongest reaction in the summer, and subsequently became weak with the drop in temperature to winter. Also, the SRPC of the lizard showed distinct seasonal variations in number and size of the dense-cored vesicles correlated to the serotonin immunoreactivity. In contrast, the changes in size of the lysosomes and nucleoli of the SRPC were inversely proportional to that of the dense-cored vesicles. Furthermore, the lysosomes ingested some dense-cored vesicles after the autumn, and they coalesced to form huge autophagosomes or residual bodies during the winter. The present study provided serotonin-immunohistochemical and ultrastructural evidence for seasonal variations in the secretory activity of the lizard pineal organ in accordance with changes in the environmental temperature. However, there may be few functional relationships between the pineal gland and the reproductive organs in the male Japanese lizard in relation to environmental temperature.

Animals↗
PubMed2003

Variable ecological effects of hurricanes: the importance of seasonal timing for survival of lizards on Bahamian islands.

Two recent hurricanes passed directly over the northern Bahamas 2 years apart, allowing a comparison of their effects on lizard populations inhabiting exactly the same islands. The hurricanes differed in two ways: one struck during the reproductive season and was relatively severe; the other struck after most reproduction had taken place and was milder. The late-season hurricane produced a significant relation between population reduction and lowness of the island that lasted at least through two seasons; the earlier hurricane produced no such relationship. The late-season hurricane wiped out populations of lizards on two islands (two of the three lowest) that the earlier hurricane failed to exterminate even though it was stronger. We relate these effects to the fact that the study lizards regenerated from the earlier hurricane only via the egg stage, whereas eggs were unavailable when the later storm struck and regeneration was via hatched lizards. We discriminate and illustrate four kinds of hurricanes, cross-classified by two contrasts: earlier vs. later and stronger vs. weaker. A later, stronger hurricane completely exterminated lizard populations at a second Bahamian site, whereas an earlier, weaker hurricane had no detectable effect at a third Bahamian site. We suggest that, in addition to severity, the timing of a hurricane as it coincides with reproductive scheduling or other phenological aspects may determine the magnitude of its effect on a variety of organisms.

Animals↗
PubMed2004

Effectiveness of the defence mechanism of the turnip sawfly, Athalia rosae (Hymenoptera: Tenthredinidae), against predation by lizards.

The turnip sawfly, Athalia rosae Linnaeus, is a pest on cruciferous crops. Larvae sequester secondary plant compounds, namely glucosinolates, in their haemolymph. When attacked, their integument is easily disrupted and a droplet of haemolymph is exuded ('easy bleeding'). This has been shown to be an effective, chemical-based, defence against invertebrate predators. The efficiency of this proposed defence was tested against a vertebrate predator, using groups of the iguanid lizard Anolis carolinensis Voigt as a model predator. Caterpillars of Pieris rapae Linnaeus and Pieris brassicae Linnaeus served as control prey species that do not sequester glucosinolates. Lizards attacked far fewer sawfly larvae than pierid caterpillars. Several of the sawfly larvae were rejected after an initial attack, demonstrating unpalatability to the lizards, while the Pieris larvae were not rejected. However, P. rapae larvae topically treated with extracts of haemolymph of A. rosae had no deterrent effect on the lizards and no avoidance learning occurred over a period of two weeks. Adult sawflies do not easy bleed but have glucosinolates carried over from the larval stage. Lizards attacked them at a higher rate than larvae and they were never rejected. The results suggest that for the defensive effectiveness of the pest sawfly species against vertebrates the chemical cue is not necessarily sufficient. Movement and colour may be important additional factors triggering the behaviour of vertebrate predators.

Adaptation, Physiological↗
PubMed2006

The circadian system of ruin lizards: a seasonally changing neuroendocrine loop?

Previous studies have shown that the amplitude of daily melatonin production in cultured ruin lizard pineal organs explanted in the summer is significantly higher than that from organs explanted in the winter. To test whether seasonal photoperiodic changes are decoded autonomously by the pineal gland, pineals explanted in summer were cultured in vitro and exposed to changes between winter and summer photoperiods. The changes in photoperiod duration did not affect the daily profiles of in vitro melatonin production. The discrepancy between the present in vitro results and those from lizards exposed to winter or summer photoperiods before pineal explantation supports the view that circadian information entering the pineal gland via its innervation is involved in determining seasonal changes of melatonin production in ruin lizards. We further examined whether a central component of the circadian system of ruin lizards, specifically the retinae of the lateral eyes, expresses similar seasonal changes in function as does the pineal gland. We did not find any difference between summer and autumn-winter in the effectiveness of either bilateral retinalectomy or optic nerve lesion-at the level of the optic chiasm-in altering circadian locomotor behavior in constant conditions. Both surgical procedures mostly induced a shortening of the free-running period of the locomotor rhythm of similar magnitude in all seasons. Thus, the retinae do not appear to participate in the seasonal reorganization of the circadian system in ruin lizards.

Animals↗
PubMedDate not supplied

Variation in metabolic rate between populations of a geographically widespread lizard.

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.

Adaptation, Physiological↗
PubMedDate not supplied

Lizards, lipids, and dietary links to animal function.

Our experiments were designed to test the hypotheses that dietary lipids can affect whole-animal physiological processes in a manner concordant with changes in the fluidity of cell membranes. We measured (1) the lipid composition of five tissues, (2) body temperatures selected in a thermal gradient (T(sel)), (3) the body temperature at which the righting reflex was lost (critical thermal minimal [CTMin]), and (4) resting metabolic rate (RMR) at three body temperatures in desert iguanas (Dipsosaurus dorsalis) fed diets enriched with either saturated or unsaturated fatty acids. The composition of lipids in tissues of the lizards generally reflected the lipids in their diets, but the particular classes and ratios of fatty acids varied among sampled organs, indicating the conservative nature of some tissues (e.g., brain) relative to others (e.g., depot fat). Lizards fed the diet enriched with saturated fatty acids selected warmer nighttime body temperatures than did lizards fed a diet enriched with unsaturated fatty acids. This difference is concordant with the hypothesis that the composition of dietary fats influences membrane fluidity and that ectotherms may compensate for such changes in fluidity by selecting different body temperatures. The CTMin of the two treatment groups was indistinguishable. This may reflect the conservatism of some tissues (e.g., brain) irrespective of diet treatment. The RMR of the saturated treatment group nearly doubled between 30 degrees and 40 degrees C. Here, some discrete membrane domains in the lizards fed the saturated diet may have been in a more-ordered phase at 30 degrees C and then transformed to a less-ordered phase at 40 degrees C. In contrast, the RMR of the unsaturated treatment group exhibited temperature independence in metabolic rate from 30 degrees to 40 degrees C. Perhaps the unsaturated diet resulted in membranes that developed a higher degree of disorder (i.e., a certain phase) at a lower temperature than were membranes of lizards fed the saturated diet. Our study demonstrates links between dietary fats and whole-animal physiology; however, the mechanistic basis of these links, and the general knowledge of lipid metabolism in squamate reptiles, remain poorly understood and warrant further study.

Adaptation, Physiological↗
PubMedDate not supplied

Influence of heat transmission mode on heating rates and on the selection of patches for heating in a mediterranean lizard.

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.

Animals↗
PubMedDate not supplied

Intersexual differences in energy expenditure of Anolis carolinensis lizards during breeding and postbreeding seasons.

Although the amount of energy that males and females invest in reproduction is an integral component of theories explaining the evolution of particular mating strategies, few studies have actually determined the amount of energy that each sex allocates to reproduction. We compared how energy is expended by male and female Anolis carolinensis lizards during both the breeding and postbreeding seasons. We used laboratory respirometry to determine resting metabolic rates (RMRs) of inactive, freshly captured lizards and the doubly labeled water technique to determine field metabolic rates (FMRs) of free-ranging lizards. Both RMRs and FMRs were influenced by body mass but not by sex. Season did not influence FMRs; however, RMRs of both sexes increased approximately 40% from the breeding to the postbreeding season. The seasonal increase in RMRs was attributed to a postreproductive increase in feeding rate and specific dynamic action. We used RMRs, FMRs, and thermal profiles of lizards to calculate energy budgets for breeding and postbreeding seasons. Energy budgets partitioned daily field energy (DFE; calculated from FMRs) into daily activity energy (DAE) and daily resting energy (DRE; calculated from RMRs). Energy expended for reproduction was estimated as DAE during the breeding season plus egg production (for females). Despite males having 40% greater body mass, females expended 46% more energy for reproduction than did males (906 and 619 J/d, respectively). Total metabolizable energy (TME=DFE+egg production for females) expended during the breeding season was similar for males and females (1,280 and 1,365 J/d, respectively). Although TME of females decreased 44% from the breeding to the postbreeding season (1,365 vs. 766 J/d), TME of males was similar during both seasons (1,280 vs. 1,245 J/d). There were both seasonal and sexual differences in DRE and DAE. Compared with most lizards from semiarid/desert habitats, A. carolinensis in a temperate habitat expends more total energy during the breeding season, allocates more energy to eggs, and appears to have more total energy available for reproduction.

Analysis of Variance↗
PubMed1999

Field test of a paradigm: hysteresis of heart rate in thermoregulation by a free-ranging lizard (Pogona barbata).

The discovery that changes in heart rate and blood flow allow some reptiles to heat faster than they cool has become a central paradigm in our understanding of reptilian thermoregulation. However, this hysteresis in heart rate has been demonstrated only in simplistic laboratory heating and cooling trials, leaving its functional significance in free-ranging animals unproven. To test the validity of this paradigm, we measured heart rate and body temperature (Tb) in undisturbed, free-ranging bearded dragons (Pogona barbata), the species in which this phenomenon was first described. Our field data confirmed the paradigm and we found that heart rate during heating usually exceeded heart rate during cooling at any Tb. Importantly, however, we discovered that heart rate was proportionally faster in cool lizards whose Tb was still well below the 'preferred Tb range' compared to lizards whose Tb was already close to it. Similarly, heart rate during cooling was proportionally slower the warmer the lizard and the greater its cooling potential compared to lizards whose Tb was already near minimum operative temperature. Further, we predicted that, if heart rate hysteresis has functional significance, a 'reverse hysteresis' pattern should be observable when lizards risked overheating. This was indeed the case and, during heating on those occasions when Tb reached very high levels (> 40 degrees C), heart rate was significantly lower than heart rate during the immediately following cooling phase. These results demonstrate that physiological control of thermoregulation in reptiles is more complex than has been previously recognized.

Animals↗