Influence of drying time on nematode eggs in scats of scincid lizard Egernia stokesii

Two pharyngodonid nematode species, Pharyngodon tiliquae and Thelandros trachysauri, infect the Australian lizard Egernia stokesii (gidgee skink) in populations from South Australia. Eggs are detected in lizard scats that are deposited in piles outside the rock crevice refuges that the lizards occupy. Eggs were isolated by salt flotation from fresh scats and from scats that had been dried in simulated field conditions for 7, 14, 21, and 28 days. Egg counts decreased with drying time for both nematode species, but T. trachysauri eggs were still detected after 28 days of drying, whereas P. tiliquae eggs were rarely detected after 14 days. These results suggest that egg counts can be used to infer host infection status only from relatively fresh scats and that eggs of the 2 species persist in a state where they can be detected by standard flotation techniques, for different times.     

Head-body temperature differences in the Australian blue-tongued lizard, Tiliqua scincoides during radiant heating

When heated radiantly, head-body temperature gradients developed in both live and dead Tiliqua scincoides. The gradients were consistently larger in live than in dead individuals, indicating they were enhanced by a physiological component superimposed on the more basic physical components. Large gradients in the initial phases of heating represented a lag effect, the head core beginning to receive heat before the body core because it is closer to the heated surface. Once this lag effect subsided, the body heated more rapidly than the head because it presented a greater incident surface area per unit mass than did the head. Living lizards appeared to maintain head-body temperature differences until the maximum voluntary temperature was approached.     

Energetic costs of prey ingestion in a scincid lizard,Scincella lateralis

Summary The relative importance of aerobic and anaerobic metabolism during feeding was investigated in the ground skink, Scincella lateralis. Animals were fed crickets of three different sizes relative to body mass (5, 10, and 15% of body mass). Oxygen consumption and lactic acid production of animals during feeding were compared with those of animals at rest and when exercising intensely. Oxygen consumption was higher in feeding and exercising animals than in those at rest. Rates of oxygen consumption of animals consuming prey of 5 and 10% of body mass were not significantly different from each other, but were lower than rates of animals consuming prey of 15% of body mass. Lactic acid concentrations in feeding animals increased with increasing prey size. Concentrations in resting and feeding animals were not different, but those of exercising animals were significantly higher. These data suggest that, despite a positive correlation between prey size and lactic acid concentration, anaerobiosis is relatively unimportant in the support of prey handling for Scincella lateralis. The energetic requirements of feeding in this species are met largely by increased aerobic metabolism.     

Energetic costs of tail loss in a montane scincid lizard

Most species of lizards will shed their tails at the point of contact when grasped by a predator. We investigated the energetic consequences of tail loss by measuring lipids in a scincid lizard that stores energy in its tail for reproduction. Most of the lipids were concentrated in the proximal portion of the tail. Thus, partial tail loss may not severely affect energy stores if the distal portion of the tail is shed in predatory encounters. We also found that the width of the tail was a reliable non-invasive index of energy reserves in this species.     

Deferred agonistic behavior in a long-lived scincid lizard Eumeces laticeps

Summary A laboratory experiment with the broad-headed skink (Eumeces laticeps) involving staged agonistic encounters demonstrates that larger males have an advantage over smaller ones in agonistic bouts. Field data on head wounds produced by intraspecific fighting during the breeding season show a much higher frequency of new wounds among males over 100 mm in snout-vent-length than in smaller males. The significant difference in new-wound frequency strongly suggests avoidance of fights by the small males, which is corroborated by laboratory and field observations. Access by males to reproductively active females depends on the ability to defeat other males in aggressive contests virtually always involving head biting if the males are of nearly equal size. Because the probability of winning agonistic encounters increases with size, young males avoid fights with older males. Aggressive contests with larger males and reproductive attempts other than courtship in the absence of larger males are deferred.Aggressive behavior in E. laticeps may be employed in direct defense of females, but might also be expressed in defense of specific sites and/or territories. In the laboratory, males in their home cages were significantly more likely to win encounters with males of similar size than were males fighting in the home cages of opponents. This suggests that encounter site could be important in determining encounter outcome and that field study of possible site defense or territoriality is needed.     

The influence of hydric environments during egg incubation on embryonic heart rates and offspring phenotypes in a scincid lizard (Lampropholis guichenoti)

Extensive evidence shows that incubation conditions can affect phenotypic traits of hatchling reptiles, but the relative importance of thermal versus hydric factors, and the proximate mechanisms by which such factors influence hatchling phenotypes, remain unclear for most species. We incubated eggs of an Australian scincid lizard, Lampropholis guichenoti, at four different moisture contents ranging from -500 to 0 kPa. Drier substrates reduced water uptake of eggs and resulted in smaller hatchlings, but other phenotypic traits (incubation periods, hatchling sex, body proportions, running speeds, growth rates post-hatching) were not affected by the hydric environment during incubation. Contrary to our prediction, lower water uptake during incubation (and hence, presumably, more viscous blood) did not affect embryonic heart rates. Thus, as in many other squamate species, hatchling phenotypes and embryonic developmental rates of L. guichenoti are less sensitive to hydric conditions in the nest than to thermal regimes.     

Sex differences in optimal incubation temperatures in a scincid lizard species

Most theoretical models for the evolution of temperature-dependent sex determination (TSD) rely upon differential fitness of male and female offspring incubated under different thermal regimes. However, there are few convincing data on this topic. We studied incubation effects in a lizard species (Bassiana duperreyi, Scincidae) with genotypic sex determination, so that we could separate effects due to incubation temperatures from those due to offspring gender. We incubated eggs under two different fluctuating-temperature regimes that simulated hot and cold natural nest-sites. The effects of our incubation treatments on phenotypes of the hatchling lizards (morphology and locomotor performance) differed between the sexes. Females emerging from eggs exposed to the “hot nest” treatment (diel cycling, 23–31°C) were larger, and ran faster, than did their sisters from the “cold nest” treatment (16–24°C). Males showed a smaller and less consistent phenotypic response than females. These incubation-induced responses were relatively stable during the first few weeks of life post-hatching, at least in captive lizards maintained under laboratory conditions. These kinds of sex differences in the phenotypic responses of hatchling reptiles to incubation conditions provide a plausible basis for the evolution of temperature-dependent sex determination in reptiles. Received: 07 May 1998 / Accepted: 16 November 1998     

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.     

Ownership influences the outcome of male-male contests in the scincid lizard, Niveoscincus microlepidotus

Male snow skinks (Niveoscincus microlepidotus) in the Tasmanianhighlands have broadly overlapping home ranges, and fight vigorously(often with substantial damage to one or both participants)upon encountering another adult male. We observed 32 male-malecontests, involving at least 49 different males, during a five-yearfield study near the summit of Mount Wellington. Bouts involvingsimilar-sized lizards typically continued for longer than boutsinvolving a greater size disparity between the combatants. Residentmales won 72% of all bouts, despite a lack of any significantdifference between residents and intruders in body sizes, relativehead sizes or body condition. Thus, prior residency of a siteappears to be the major determinant of success in male-malerivalry.     

Geographic variation in 'costs of reproduction' in the scincid lizard Lampropholis guichenoti

1. A major focus of life-history research has been the analysis of reproductive effort (RE). However, while clearly defined in theory, RE has proved very difficult to measure. Consequently, researchers have looked for indices that estimate the components of RE. Uncritical use of indices of reproductive investment, such as measures of costs of reproduction, without verification of the underlying assumptions of the link between these traits, may lead to spurious conclusions. In this paper, the common assumption that the physical burden of the clutch impairs locomotor ability in gravid reptiles is examined.
2. Two neighbouring populations of Australian scincid lizards ( Lampropholis guichenoti) are similar in adult body sizes, body shapes and reproductive output (egg sizes, clutch sizes, relative clutch masses).
3. Despite morphological and reproductive similarities, the effects of pregnancy on maternal locomotor ability (running speeds, as measured in a laboratory raceway) differed dramatically between the two populations.
4. Lizards from the two populations ran at similar speeds when nongravid (i.e. after egg-laying), but pregnancy significantly reduced running speeds in one population and increased them in the other. Thus, superficial similarities in body size and reproductive output masked a strong divergence in the locomotor 'costs' of reproduction.
5. Caution is advised if using simple measures of reproductive output (e.g. relative clutch mass) as indices of reproductive effort, or to generalize results even among conspecific populations.     

Some properties of a pheromone allowing individual recognition, from the scats of an Australian lizard, Egernia striolata

  The Australian lizard, Egernia striolata, can distinguish its own scats from those of unfamiliar conspecific individuals. This appears to be unrelated to diet, because there is no difference in the response to scats from unfamiliar lizards fed on diets that are the same or different from the test lizard. The signal that induces the response is not a visual or tactile property of scat structure, because test lizards respond equally to crushed and intact scats. We suggest that a pheromone is secreted onto the scat as it is produced. Water solutions of scats did not contain signal components that allowed lizards to distinguish their own scats from others. However, solutions of scats in dichloromethane (DCM) retained unique characteristics, and test lizards responded more strongly to the solution from scats of an unfamiliar lizard that to the solution from their own scats. Further fractionation of the DCM solution in pentane and in methanol led to loss of the unique signals needed for individual recognition, but those were restored when the pentane and methanol fractions were recombined. We infer that these lizards can distinguish between scats of different individuals on the basis of signals they receive from a complex combination of chemicals. Received: 14 December 1998 / Received in revised form: 9 April 1999 / Accepted: 12 April 1999     

Clutch size in the tropical scincid lizard Emoia sanfordi, a species endemic to the Vanuatu Archipelago

The majority of species in the scincid genus Emoia (Squamata: Scincidae) have a fixed clutch size of two eggs per clutch and produce between two and four clutches per year. One lineage within Emoia, the Emoia samoensis species group, consists of 13 species occurring in Melanesia and the islands of the southwestern Pacific Ocean, and exhibits variation in clutch size, with previously reported clutch sizes of two to five eggs. Little is known about reproduction in several members of this lineage including Emoia sanfordi, a large-bodied lizard endemic to the archipelago of Vanuatu in the South Pacific. We analyzed reproduction and clutch size in E. sanfordi females and discovered that there is a substantial amount of intraspecific variation, with clutch size ranging from two to seven eggs, with a modal clutch size of five eggs. Females were reproductively active throughout the study period of June through October and appear to be laying multiple clutches. The variation in clutch size seen in E. sanfordi is congruent with the variation previously reported within other closely related species.     

Tooth development in a scincid lizard, Chalcides viridanus (Squamata), with particular attention to enamel formation

Comparative analysis of tooth development in the main vertebrate lineages is needed to determine the various evolutionary routes leading to current dentition in living vertebrates. We have used light, scanning and transmission electron microscopy to study tooth morphology and the main stages of tooth development in the scincid lizard, Chalcides viridanus, viz., from late embryos to 6-year-old specimens of a laboratory-bred colony, and from early initiation stages to complete differentiation and attachment, including resorption and enamel formation. In C. viridanus, all teeth of a jaw have a similar morphology but tooth shape, size and orientation change during ontogeny, with a constant number of tooth positions. Tooth morphology changes from a simple smooth cone in the late embryo to the typical adult aspect of two cusps and several ridges via successive tooth replacement at every position. First-generation teeth are initiated by interaction between the oral epithelium and subjacent mesenchyme. The dental lamina of these teeth directly branches from the basal layer of the oral epithelium. On replacement-tooth initiation, the dental lamina spreads from the enamel organ of the previous tooth. The epithelial cell population, at the dental lamina extremity and near the bone support surface, proliferates and differentiates into the enamel organ, the inner (IDE) and outer dental epithelium being separated by stellate reticulum. IDE differentiates into ameloblasts, which produce enamel matrix components. In the region facing differentiating IDE, mesenchymal cells differentiate into dental papilla and give rise to odontoblasts, which first deposit a layer of predentin matrix. The first elements of the enamel matrix are then synthesised by ameloblasts. Matrix mineralisation starts in the upper region of the tooth (dentin then enamel). Enamel maturation begins once the enamel matrix layer is complete. Concomitantly, dental matrices are deposited towards the base of the dentin cone. Maturation of the enamel matrix progresses from top to base; dentin mineralisation proceeds centripetally from the dentin–enamel junction towards the pulp cavity. Tooth attachment is pleurodont and tooth replacement occurs from the lingual side from which the dentin cone of the functional teeth is resorbed. Resorption starts from a deeper region in adults than in juveniles. Our results lead us to conclude that tooth morphogenesis and differentiation in this lizard are similar to those described for mammalian teeth. However, Tomes processes and enamel prisms are absent.     

Physiological and behavioral control of heating and cooling rates in rubber boas, Charina bottae

1. We examined the ability of rubber boas (Charina bottae) to physiologically and behaviorally control their heating and cooling rates between 5 and 35 °C with constrained and unconstrained postural treatments.     

The adaptive significance of colour pattern polymorphism in the Australian scincid lizard Lampropholis delicata

Females of Lampropholis delicata are dimorphic for colour pattern, the difference between morphs being the presence or absence of a distinct white mid-lateral stripe. A less distinct striped morph occurs also in males. We evaluated alternative hypotheses for the maintenance of this polymorphism by examining temporal and spatial variation in morph frequency, testing for differential selection among morphs using data on body size and reproductive traits from preserved specimens, and experimentally manipulating colour pattern in free-ranging lizards of both sexes, to assess the influence of the lateral stripe on survival rates. We found that the relative frequency of striped individuals varied among populations and decreased from north to south in both sexes, coincident with an increasing incidence of regenerated tails. Morph frequencies did not change through time within a population. Striped gravid females appeared to survive better and produced larger clutches than did non-striped females. In our experimental study, the relationship between survival and colour morph differed between the two sexes; males painted with a white lateral stripe had lower survival than control (brown stripe) males, but survival did not differ between striped and control females. The different response in the two sexes may be due partly to differences in temperature and microhabitat selection. We propose that the white lateral stripe decreases susceptibility to predators in gravid females but increases risk of predation in males, especially in combination with low temperatures. The polymorphism might be maintained by: (1) opposing fitness consequences of the stripe in males and females; (2) sex-specific habitat selection; and (3) gene flow in combination with spatial variation in relative fitness of the two morphs.