Young Lizards Research Articles

Sex Determination in Immature Sierra Nevada Lizard (Timon nevadensis).

Simple SummarySex determination in reptiles is frequently requested by reptile breeders, and it is a real challenge in reptiles with little or no sexual dimorphism, such as in immature subjects. Twenty-three clinically healthy young Sierra Nevada lizards (Timon nevadensis) aged between 4 and 6 months were included for sex determination using two techniques: cloacal probing and contrast radiography. Results showed that contrast radiography may have major sensitivity for sex determination compared to probing. Given the above, this technique could represent a valid and less invasive aid for sexing young lizards.Sex determination has a fundamental role in a captive breeding context, both for commercial reasons and in relation to animal welfare itself. However, this can be particularly difficult, especially in reptiles with little or no sexual dimorphism. Twenty-three clinically healthy young Sierra Nevada lizards (Timon nevadensis) were included in this study for sex determination. The first attempt at sexing was carried out by cloacal probing. A small, buttoned probe was inserted very gently into the hemipenal pouches, and the length of the inserted part was evaluated and measured. Subsequently, for each animal, a contrast medium was administered into the cloaca, and radiography was performed within 5 min. Through probing, 11 males and 8 females were recognized. The test was, however, equivocal in four subjects. In contrast radiography, 14 males and 9 females were identified. All the animals were rechecked after 8 months through an ultrasound examination, confirming 15 of the 14 previously male sexed animals based on contrast radiography. All the animals identified as female (n = 9) by contrast radiography were confirmed. From these results, it seems that contrast radiography may have major sensitivity in sex determination compared to probing. This technique could represent a valid and less invasive aid for sexing young lizards.

Great capricorn beetle-created corridors as refuges for lizards

Ecosystem engineering is among the most important factors shaping ecosystems; however, it remains largely unstudied. Here, we present observations on three lizard species, the common lizard Zootoca vivipara, the sand lizard Lacerta agilis, and the slow worm Anguis fragilis, which use habitats created by the great capricorn beetle, Cerambyx cerdo. These galleries are heavily used by the common lizards and young sand lizards. We discuss the possible advantages of such beetle-created habitats for reptiles: antipredator refuges, hibernation sites, thermoregulatory behaviour, and preying activities. Since previous studies have reported numerous invertebrate species as well as vertebrates (including bats and snakes) in these refugia, we find the great capricorn beetle-inhabited oaks as potentially important microhabitats for a variety of animals.

Incubation environment impacts the social cognition of adult lizards.

Recent work exploring the relationship between early environmental conditions and cognition has shown that incubation environment can influence both brain anatomy and performance in simple operant tasks in young lizards. It is currently unknown how it impacts other, potentially more sophisticated, cognitive processes. Social-cognitive abilities, such as gaze following and social learning, are thought to be highly adaptive as they provide a short-cut to acquiring new information. Here, we investigated whether egg incubation temperature influenced two aspects of social cognition, gaze following and social learning in adult reptiles (Pogona vitticeps). Incubation temperature did not influence the gaze following ability of the bearded dragons; however, lizards incubated at colder temperatures were quicker at learning a social task and faster at completing that task. These results are the first to show that egg incubation temperature influences the social cognitive abilities of an oviparous reptile species and that it does so differentially depending on the task. Further, the results show that the effect of incubation environment was not ephemeral but lasted long into adulthood. It could thus have potential long-term effects on fitness.

Curvilinear telomere length dynamics in a squamate reptile

Summary The lack of consensus concerning the impact of telomere length (TL) dynamics on survival emphasizes the need for additional studies to evaluate the effect of TL on key life‐history processes. Using both cross‐sectional and longitudinal data, we therefore explored age‐specific TL dynamics in a squamate reptile: the frillneck lizard (Chlamydosaurus kingii). Our cross‐sectional analyses revealed that young lizards had short TL, TL increased in medium‐aged lizards, but TL decreased in older age cohorts, revealing a curvilinear relationship between TL and frillneck lizard age. Neither our cross‐sectional nor our longitudinal analyses revealed any association between TL dynamics and lizard survival. We observed a significant positive relationship between TL and telomerase expression (TE), suggesting that TE is a significant determinant of frillneck lizard TL dynamics. Importantly, our longitudinal analyses revealed a positive relationship between initial TL and telomere attrition rate within individual lizards, that is lizards with short initial telomeres were subjected to reduced telomere attrition rates compared to lizards with long initial TL. Our results strongly suggest that TL and TE dynamics in frillneck lizards is not associated with lizard survival but rather reflect an adaptation to maintain TL above a critical minimum length in order to sustain cellular homeostasis. A lay summary is available for this article.

Egg incubation effects generate positive correlations between size, speed and learning ability in young lizards

Previous studies have suggested that body size and locomotor performance are targets of Darwinian selection in reptiles. However, much of the variation in these traits may derive from phenotypically plastic responses to incubation temperature, rather than from underlying genetic variation. Intriguingly, incubation temperature may also influence cognitive traits such as learning ability. Therefore, we might expect correlations between a reptile's size, locomotor speed and learning ability either due to selection on all of these traits or due to environmental effects during egg incubation. In the present study, we incubated lizard eggs (Scincidae: Bassiana duperreyi) under 'hot' and 'cold' thermal regimes and then assessed differences in hatchling body size, running speed and learning ability. We measured learning ability using a Y-maze and a food reward. We found high correlations between size, speed and learning ability, using two different metrics to quantify learning (time to solution, and directness of route), and showed that environmental effects (incubation temperature) cause these correlations. If widespread, such correlations challenge any simple interpretation of fitness advantages due to body size or speed within a population; for example, survivors may be larger and faster than nonsurvivors because of differences in learning ability, not because of their size or speed.

LIZARD WITS INCREASE AS PLANET HEATS

We all know an animal is the product of its genes and the influence of the environment. Humidity, food availability and parental care are just examples of factors that can have a strong impact on an animal's characteristics. This is certainly true in the case of reptiles, where incubation temperature can affect several of their physical and physiological characteristics. It is well known, for example, that sex, size and running speed can all be influenced by temperature in various lizard species. But what about other, less-obvious characteristics? It is harder to measure how incubation temperature affects different aspects of behaviour and intelligence. None the less, these are interesting questions and Joshua Amiel and Richard Shine from the University of Sidney, Australia, decided they were worth pursuing.They wanted to know whether incubation temperature affected young lizards' ability to learn. Moreover, they wanted to know whether an increased ability to learn would be relevant during a life-threatening situation. To do this, Amiel and Shine collected gravid three-lined skinks, which are lizards native to Australian forests. They took them back to their lab in Sidney and incubated their eggs at cold (16±7.5°C) and hot (22±7.5°C) regimes. When the babies hatched, it was time for their IQ tests inside their own homes so that they would not have to deal with the additional stress of learning in a strange environment. Each enclosure had two small hiding retreats but the entrance to one of them was blocked with a piece of Plexiglas. For each test a baby lizard was placed right in the middle between the two retreats under a little plastic cover. As soon as the experimenter lifted the cover, he tickled the lizard's tail with a paintbrush, scaring the poor lizard, which ran for a hiding place. The scientists then counted the number of times that the hatchling chose the wrong hide and the time it took to finally find the available retreat. They repeated these trials for 4 days, four times a day with each lizard and then compared the reptiles' success rates through time. Were they learning?All the babies were capable of learning and made fewer mistakes the more tests they performed, but as time went by, the hatchlings that had been incubated in the hot environment learned faster and made fewer mistakes than the cold-incubated ones. This was independent of sex, size or running speed.The fact that warm-incubated lizards turned out to be smarter than cold-incubated lizards gives a glimpse of what might happen during global warming. Amiel and Shine point out that this increased ability to learn will increase the lizard's capacity to respond in the face of environmental changes and therefore increase their chances of survival. The study does not dismiss the possibility that cold-incubated lizards may ‘catch up’ with their warm-incubated counterparts as they develop, or even compensate for their slower wits with other abilities such as locomotor speed. However, this does not negate the fact that lizards from hot eggs have the edge over their cool-egg friends.

Thermal regimes during incubation do not affect mean selected temperatures of hatchling lizards ( Bassiana duperreyi, Scincidae)

Incubation temperatures profoundly affect many phenotypic traits of squamate reptiles, and mean selected body temperatures of such animals also are plastic in response to environmental factors. Plausibly, then, incubation temperatures might affect hatchling thermoregulation, either via adaptation (i.e., populations that historically experience different nest conditions, also will diverge in hatchling thermoregulatory behaviour) or phenotypic plasticity (incubation temperatures directly modify hatchling behaviours). We tested this hypothesis with a montane scincid lizard ( Bassiana duperreyi), using thermal-imaging methods to quantify temperatures (of both head and body) selected by hatchling lizards. The young lizards kept their heads cooler than their bodies, but mean selected temperatures did not differ among hatchlings from three populations with differing thermal regimes in natural nests, nor were they affected by thermal conditions during incubation. The conservatism of mean selected temperatures stands in strong contrast to the lability of many other phenotypic traits in response to incubation temperatures in this species.

Vitamin E Does Not Elevate Survival in Free-Ranging Lizards

Free radical theory predicts that the unavoidable production of reactive molecules as a by-product of the respiratory transport chain will pathologically affect organismal function and fitness and lead to disease and a shortened life span. This suggests that free radical production may be linked to metabolic rate, which in turn relates to foraging strategies and intrinsic growth rate and could therefore be important for directing the evolution of life histories. We designed an experiment in which young lizards (Australian Painted Dragons, Ctenophorus pictus) received an implant with α-Tocophorol (Vitamin E) or control vehicle (cocoa butter). They were released into the wild and monitored for survival. Recapture rate was eight per cent for vitamin E-treated lizards and 16 per cent for controls, resulting in no significant difference in probability of being recaptured. We discuss the importance of dose-dependence and context-dependent effects of this supplementation and outline other physiological factors that may be driving mortality rates in young lizards.

18.P3. Seasonal changes in the functional capacity of the midgut associated with long term fasting and hypometabolism in young tegu lizards Tupinambis merianae

18.P3. Seasonal changes in the functional capacity of the midgut associated with long term fasting and hypometabolism in young tegu lizards Tupinambis merianae

The functional significance of residual yolk in hatchling lizards Amphibolurus muricatus (Agamidae)

Summary Although post‐hatching parental care is uncommon in reptiles, reproducing females may none the less contribute to the nutritional state of their offspring by depositing more yolk into the egg than is needed for embryogenesis. This ‘extra’ yolk (i.e. residual yolk) is drawn into the offspring's body prior to hatching and is widely assumed to serve as an energy resource for early life activities. However, empirical data on the functional significance of residual yolk are rare. We surgically removed residual yolk from hatchling lizards Amphibolurus muricatus to evaluate its effects on offspring growth and survival over 4 weeks under two environmental conditions: low or high food abundance. Unsurprisingly, higher food abundance enhanced growth rates of the young lizards. However, experimental removal of residual yolk did not affect any of the traits that we measured in either nutritionally harsh or benign post‐hatching environments. Overall, our results challenge the common assumption that residual yolk is an important source of energy during early life in lizards, and suggest instead that residual yolk is of trivial nutritional significance (especially, relative to prey availability). Residual yolk in A. muricutus may instead have a different (non‐nutritive) function, or be a nonfunctional relict retained through phylogenetic conservatism from ancestral taxa.

Effects of Constant Lightness, Darkness and Parachlorophenylalanine Treatment on Tail Regeneration in the Lizard Ophisops elegans macrodactylus: Macroscopic, Biochemical and Histological Changes

A better understanding of regenerative growth is very important for the development of new potential strategies. Recently, the pineal secretory product melatonin was shown to stimulate the regeneration process. In this study, we carried out an experimental investigation of tail regeneration in young adult lizards, Ophisops elegans macrodactylus Berthold, 1842, addressing the role of melatonin on the regeneration process. Lizards were divided into three groups: constant light-exposed control group (n = 13), constant dark-exposed group (n = 15) and parachlorophenylalanine (p-CPA) treatment group exposed to constant light (n = 15). Using a tail autotomy procedure, the effects of p-CPA treatment on connective tissue together with neural tissue and vascular tissue in regenerating tail in lizards were investigated. p-CPA (400 microg/kg body mass) was injected from day 0 to 30 days after autotomy. p-CPA treatment produced a significant increase in the length of the regenerated tail compared with light-exposed control and dark-exposed lizards. Total collagen content was found to be higher in p-CPA-treated animals in comparison with other groups. Histologically, a higher percentage of connective tissue and vascular tissue and a lower percentage of neural tissue were found in the regenerated tails of the p-CPA-treated lizards. Importantly, the percentage of neural tissue in lizards in the dark-exposed animals was higher than that in animals of both light-exposed and p-CPA treatment groups. Thus, it is clear that p-CPA has a stimulatory influence on fibroblast collagen production and vascularization of the regenerated tail in the lizards. Furthermore, it seems that the neural regeneration process was markedly enhanced in lizards exposed to continuous darkness. Based on the results of our study, it is suggested that melatonin may be an active factor that speeds up the rate of tail regeneration in lacertilians.

Post-hatching environment contributes greatly to phenotypic variation between two populations of the Australian garden skink, Lampropholis guichenoti

While recent experimental work on a variety of reptile species has demonstrated that incubation temperature influences hatchling phenotypes, the biological significance of such phenotypic variation remains unclear. Incubation temperature may exert significant long-term phenotypic effects. Alternatively, such influences may be temporary, or negligible relative to effects induced by genetic factors, or by the environmental conditions experienced after hatching. Even if incubation temperature exerts long-term effects on phenotype, this might occur indirectly (by influencing hatching dates) rather than by direct modifications of developmental processes. We quantified the influences of the source population, incubation temperature and rearing environment, on the phenotype of the Australian garden skink (Lampropholis guichenoti) from populations that differ in nest temperature and phenotype. Intcrpopulation differences in the phenotypes of young lizards were found to be a product of all three factors. However, the long-term effects of both population and incubation temperature operated indirectly (through variation in the date of hatching) rather than directly (through genetic or developmental factors). That is, once all temporal effects were removed, the only discernible influence on juvenile phenotypes was their rearing environment. Thus, some of the most important influences on lizard phenotypes may operate via modifications of hatching date.

Post-hatching environment contributes greatly to phenotypic variation between two populations of the Australian garden skink, Lampropholis guichenoti

While recent experimental work on a variety of reptile species has demonstrated that incubation temperature influences hatchling phenotypes, the biological significance of such phenotypic variation remains unclear. Incubation temperature may exert significant long-term phenotypic effects. Alternatively, such influences may be temporary, or negligible relative to effects induced by genetic factors, or by the environmental conditions experienced after hatching. Even if incubation temperature exerts long-term effects on phenotype, this might occur indirectly (by influencing hatching dates) rather than by direct modifications of developmental processes. We quantified the influences of the source population, incubation temperature and rearing environment, on the phenotype of the Australian garden skink (Lampropholis guichenoti) from populations that differ in nest temperature and phenotype. Interpopulation differences in the phenotypes of young lizards were found to be a product of all three factors. However, the long-term effects of both population and incubation temperature operated indirectly (through variation in the date of hatching) rather than directly (through genetic or developmental factors). That is, once all temporal effects were removed, the only discernible influence on juvenile phenotypes was their rearing environment. Thus, some of the most important influences on lizard phenotypes may operate via modifications of hatching date.

Reproductive biology of the skinkScincus mitranus(Anderson, 1871) in the central region of Saudi Arabia

The reproductive cycle ofScincus mitranuswas examined using specimens obtained from the slopes of sand dunes around Riyadh. The reproductive season was in May and June. Young lizards were observed in late September, suggesting the presence of only one clutch during the reproductive season. Data on seasonal cycles in testes, ovaries and fat bodies are given.

Food habits of the green lizard, Lacerta bilineata, in central Italy and a reliability test of faecal pellet analysis

Food habits of the green lizard (Lacerta bilineata) were studied in some Mediterranean sites of the vicinities of Rome (Latium, central Italy), by means both of stomach dissection of individuals found already dead in the field and faeces analysis of living individuals. The taxonomic diet composition of the lizards was accurately described by both methods, thus demonstrating the reliability of faecal pellet analysis as an non‐cruel method to study lizard diets. However, by using the faeces analysis technique, it is difficult to measure the exact food intake rate (items / unit of time) as well as the size distribution of prey ingested by lizards. There was a remarkable ontogenetic change in the taxonomic diet composition of green lizards: adults essentially consumed beetles and isopods, whereas juveniles fed mainly upon orthopterans, spiders, and Rhynchota. Cannibalism and predation upon small vertebrates (lizards) were very rare events. It is suggested that (i) age‐related differences in microhabitat frequented could explain the dietary differences between young and adult lizards due to different availability of the various prey categories in the various microhabitats, and that (ii) adults and juveniles partition their habitats to reduce intraspecific interference competition.

Mother–offspring recognition in two Australian lizards, Tiliqua rugosaand Egernia stokesii

Abstract. Kin recognition has been reported in many animal taxa, but rarely in lizards. Newly born clutches from two viviparous Australian skink species, Tiliqua rugosaand Egernia stokesii, were either left with their mothers, separated at birth and kept with a foster mother, or kept completely isolated from any adults. In experimental trials mothers were presented with their own and with non-related young in gauze bags, and their attention to each young lizard was measured by the number of directed tongue flicks and the time in contact. There was a consistent tendency in both species for mothers to direct more attention to their own young, whether they had been kept together or apart. Foster mothers directed more attention to their own non-familiar young than to their familiar foster young. In reciprocal experiments, young lizards of both species consistently directed more attention to their own mothers than to unrelated females, even when they had been isolated from their mothers from birth. Olfactory cues are probably important for recognition. Using these cues, lizards can recognize kin,and discriminate between kin and non-kin even if the latter have been in close association. It wasnot possible to determine if the discrimination was genetically based, or if it was acquired during orshortly after birth. The presence of mother–offspring recognition suggests that family groups maybe a component in the social organization of these species.

Maternal thermoregulation influences offspring viability in a viviparous lizard.

Gravid females of the viviparous scincid lizard Eulamprus heatwolei were maintained in the laboratory, with some females allowed to bask for 8 h/day and others for only 2 h/day. Maternal basking regimes influenced the gestation period, and significantly affected the body shapes, activity levels and running speeds of the offspring born to these females. Neonates from females with lesser basking opportunities were relatively short and fat, were very active, and were relatively fast runners. Effects of the embryos' thermal regime on the young lizards' morphology and running speed were still detectable two months after birth. Thus, much of the morphological and behavioral variation among neonatal reptiles may arise from phenotypically plastic responses to the thermal environments experienced during embryonic development, rather than from heritable genetic differences among individuals. Hence, selection on maternal thermoregulatory behavior may be an important avenue for adaptive modifications to neonatal phenotypes in reptiles.

Effect of partial water deprivation and restricted feeding on age-related changes in two enzymes of energy metabolism in the brain of male garden lizards

The lactate dehydrogenase (LDH) activity of garden lizard brain did not change with advancing age. On the other hand the succinate dehydrogenase (SDH) activity showed a decline during maturation (young to middle-aged) remaining stabilized thereafter. Seven days of partial water deprivation did not alter the LDH activity of lizards of all three age groups but caused an increase in SDH activity of old lizards only. Restricted feeding led to a decline in the activities of both the enzymes (LDH and SDH) in young lizards and an increase in LDH activity of only the old, the response in middle-aged being insignificant. The protein content of the brain did not change during maturation, but declined in old lizards. Partial water deprivation caused an increase in protein content of the brain of both middle-aged and old lizards but not in young counterparts. Only the young lizards showed an increase in protein content of the brain in response to food restriction.

Effect of two inhibitors on succinic dehydrogenase activity in cerebral hemispheres of male garden lizards of three different age groups

Age changes in the specific activity of cerebral succinic dehydrogenase (SDH) and the effect of two inhibitors (malonate and p-chlorophenoxy acetic acid) on enzyme activity were traced in a short-lived species of reptile, Calotes versicolor, the garden lizard. The enzyme activity reached a peak level in middle-aged lizards followed by a decline in old counterparts. The enzyme inhibitions by both the inhibitors were significantly higher in old than in middle-aged and young lizards suggesting a change in specificity of SDH molecules during ageing.

Changes in Catalase Activity and Its Thermolability in Liver and Kidneys of Ageing Male Garden Lizard

Catalase activity in liver and kidneys of male garden lizards remained unchanged during maturation, but showed an increase during ageing. Instead of inactivating catalase, thermal treatment at 60 +/- 1 degree C caused a marginal increase in enzyme activity in the liver of middle-aged and kidneys of young lizards with no significant effect in old counterparts. Increase in basal enzyme activity during ageing and the maintenance of resistance against thermal inactivation of the enzyme throughout the life-span support the contention that catalase molecules in lizard tissues are not altered as a function of age, a deviation from the predictions of Orgel's error catastrophe hypothesis.