Ultrastructure of epidermal sensory receptors in Amphibolurus barbatus (Lacertilis: Agamidae)

Summary The histological and ultrastructural organisation of the epidermal sensory organs in Amphibolurus barbatus has been described with respect to their position and possible functions. The sensory organs, located at the scale's edge, are most numerous in scales of the dorsal surface of the head. Most other scales of the body surface have two receptors located laterally to the spine or keel of the scale. In the imbricate scales of the ventral body region, the receptors lie just beneath the reinforced scale lip. Scanning electron microscopy has revealed the surface of the organ to be a crater lacking any surface projections. These sensory organs have a dermal papilla consisting of a nerve plexus and loose connective tissue. The nerve fibres arising from the plexus, pass to the epidermal columnar cells, where some form nerve terminals at the base of the cells, while others pass between them to form nerve terminals embedded in a superficial layer of cuboidal cells. The superficial terminals are held against the overlying keratin by masses of tonofilaments. The keratin is thickened to form a collar around the periphery of the organ but is only about 0.5 m thick immediately above it. Mechanical deformation of the scale's spine or reinforced scale lip may initiate stimulation of the nerve terminals described.     

鳄蜥捕食蜥蜴和蛇的现象

鳄蜥(Shinisaurus crocodilurus)主要捕食部分昆虫、蜘蛛、蚯蚓、小型蛙类和小鱼等,但尚未见报道鳄蜥捕食其他相对较大的动物。本文报道了鳄蜥捕食变色树蜥(Calotesversicolor)和翠青蛇(Cyclophiopsmajor)的现象,以全事件记录法观察分析了鳄蜥猎捕这两种爬行动物的行为过程。这次新发现说明鳄蜥食谱较广,具有捕食蜥蜴等个体偏大动物的能力。因此,我们建议在饲养繁育中投喂更多类型的食物以避免营养不良。     

Ciliated neurons and different types of synapses in anterior hypothalamic nuclei of reptiles

Summary The magnocellular paraventricular and supraoptic nuclei and the parvocellular preoptic and periventricular nuclei have been studied by light and electron microscopy in Emys orbicularis, Lacerta agilis and Elaphe longissima. The ultrastructure of cerebrospinal fluid (CSF)-contacting neurons was described in the preoptic and periventricular nuclei of Emys and Lacerta species. Single 9×2+0 cilia similar to those of the CSF-contacting dendritic terminals were found on perikarya of non CSF-contacting nerve cells, in all four investigated nuclei. The cilia project from funnel-like invaginations of the perikarya into the intercellular space. In the neurons of the nuclei studied, granular vesicles were found, their size being mainly 1,600 Å in the paraventricular nucleus, about 1,800 Å in the supraoptic nucleus, 1,100 Å in the periventricular nucleus and 800 Å, or up to 1,250 Å in the preoptic nucleus. In general, the neurons possess synapses of the axo-somatic, axo-somatic spine, axo-dendritic and axo-dendritic spine types. In the supraoptic nucleus, multiple interdigitated synapses were observed. Presynaptically, either synaptic vesicles only, or synaptic vesicles and dense core vesicles of different sizes (600 to 800 Å, about 1,100 Å, 1250 Å, and up to 2,000 Å) were found. It is discussed whether the above described 9×2+0 cilia may represent some kind of hypothalamic sensory structure that earlier physiological studies postulated to exist. The ciliated hypothalamic perikarya are considered by the authors to be a more differentiated form of the CSF-contacting neurons. The different types of synapses indicate multilateral connections of the nerve cells of the nuclei studied.Dedicated to Prof. Dr. Berta Scharrer on the occasion of her 70th birthday     

Nonlinearities in mating sounds of American crocodiles

We use nonlinear time series analysis methods to analyze the dynamics of the sound-producing apparatus of the American crocodile (Crocodylus acutus). We capture its dynamics by analyzing a recording of the singing activity during mating time. First, we reconstruct the phase space from the sound recording and thereby reveal that the attractor needs no less than five degrees of freedom to fully evolve in the embedding space, which suggests that a rather complex nonlinear dynamics underlies its existence. Prior to investigating the dynamics more precisely, we test whether the reconstructed attractor satisfies the notions of determinism and stationarity, as a lack of either of these properties would preclude a meaningful further analysis. After positively establishing determinism and stationarity, we proceed by showing that the maximal Lyapunov exponent of the recording is positive, which is a strong indicator for the chaotic behavior of the system, confirming that dynamical nonlinearities are an integral part of the examined sound-producing apparatus. At the end, we discuss that methods of nonlinear time series analysis could yield instructive insights and foster the understanding of vocal communication among certain reptile species.     

Quantification of three steroid hormone receptors of the leopard gecko (Eublepharis macularius), a lizard with temperature-dependent sex determination: their tissue distributions and the effect of environmental change on their expressions

Sex steroid hormones play a central role in the reproduction of all vertebrates. These hormones function through their specific receptors, so the expression levels of the receptors may reflect the responsibility of target organs. However, there was no effective method to quantify the expression levels of these receptors in reptilian species. In this study, we established the competitive-PCR assay systems for the quantification of the mRNA expression levels of three sex steroid hormone receptors in the leopard gecko. These assay systems were successfully able to detect the mRNA expression level of each receptor in various organs of male adult leopard geckoes. The expression levels of mRNA of these receptors were highly various depending on the organs assayed. This is the first report regarding the tissue distributions of sex steroid hormone receptor expressions in reptile. The effects of environmental conditions on these hormone receptor expressions were also examined. After the low temperature and short photoperiod treatment for 6 weeks, only the androgen receptor expression was significantly increased in the testes. The competitive-PCR assay systems established in this report should be applicable for various studies of the molecular mechanism underlying the reproductive activity of the leopard gecko.     

Oxidative DNA damage and antioxidant defenses in the European common lizard (Lacerta vivipara) in supercooled and frozen states

The European common lizard (Lacerta vivipara) tolerates long periods at sub-zero temperatures, either in the supercooled or the frozen state. Both physiological conditions limit oxygen availability to tissues, compelling lizards to cope with potential oxidative stress during the transition from ischemic/anoxic conditions to reperfusion with aerated blood during recovery. To determine whether antioxidant defenses are implicated in the survival of lizards when facing sub-zero temperatures, we monitored the activities of antioxidant enzymes and oxidative stress either during supercooling or during freezing exposures (20 h at -2.5 degrees C) and 24 h after thawing in two organs of lizards--muscle and liver. Supercooling induced a significant increase in the total SOD and GPx activity in muscle (by 67 and 157%, respectively), but freezing had almost no effect on enzyme activity, either in muscle or in liver. By contrast, thawed lizards exhibited higher GPx activity in both organs (a 133% increase in muscle and 59% increase in liver) and a significant decrease in liver catalase activity (a 47% difference between control and thawed lizards). These data show that supercooling (but not freezing) triggers activation of the antioxidant system and this may be in anticipation of the overgeneration of oxyradicals when the temperature increases (while thawing or at the end of supercooling). Oxidative stress was assessed from the content of 8-oxodGuo and the different DNA adducts resulting from lipid peroxidation, but it was unaltered whatever the physiological state of the lizards, thus demonstrating the efficiency of the antioxidant system that has been developed by this species. Overall, antioxidant defenses appear to be part of the adaptive machinery for reptilian tolerance to sub-zero temperatures.     

The effect of temperature on digestive and assimilation efficiency,gut passage time and appetite in an ambush foraging lizard,<Emphasis Type="Italic"> Cordylus melanotus melanotus</Emphasis>

In ectotherms, an increase in body temperature increases metabolic rate and may increase rates of digestive processes. We measured the thermal dependence of the apparent digestive and apparent assimilation efficiencies (ADE and AAE), gut passage time (GP) and appetite in Cordylus melanotus melanotus, a medium sized Crag Lizard, which is endemic to South Africa. Trials were conducted at 20, 22, 25, 30, 32 and 35 °C under controlled conditions. Trials lasted 14 days, during which, lizards were fed ca. 1 g mealworms per day. Glass beads were used as markers to determine GP at the beginning and end of trials. Faeces and urates were collected daily and oven dried at 50 °C. The energy content of egested matter was then measured using bomb calorimetry. ADE and AAE were not affected by temperature for either males or females. The mean±SE ADE and AAE were 94.4±0.3% and 87.2±0.6%, respectively. GP was not significantly different between males and females at any temperature, but decreased significantly with increasing temperature. Appetite was significantly different between the different temperatures measured. The decrease of gut passage time with increasing temperature was expected, since the digestive and assimilation efficiencies are similar over the range of temperatures tested. Lizards are thus assimilating a similar proportion of ingested energy, but at faster rates at higher temperatures. The results indicate that the digestive physiology of this species results in maximum energy gain per meal in environments where food is scarce.Abbreviations AAE apparent assimilation efficiency - ADE apparent digestive efficiency - AE assimilation efficiency - DE digestive efficiency - GP gut passage rate - NEA net energy absorbed through gut - NER net usable energy retained - SVL snout-vent length - T _b body temperature Communicated by G. Heldmaier     

The spitting behavior of two species of spitting cobras

Spitting cobras defend themselves by spitting their venom in the face of a harasser. Although it is common belief that spitting cobras direct their venom at the eyes of an aggressor, this has never been investigated. Here, we show that the spitting act of cobras (Naja nigricollis and N. pallida) can readily be triggered by a moving human face or by a moving real size photo of a human face. In contrast, a stationary human face (real or photo) or a moving or stationary human hand does not trigger the spitting act. If threatened, spitting cobras aim their venom, ejected either in two distinct jets (N. pallida) or in a fine spray (N. nigricollis), either between the eyes or at one eye. In both cobra species investigated, the width and height of the area hit by the venom was independent of eye distance (test range 5.5 cm and 11 cm). During the spitting act the cobras performed fast undulating head movements that lead to a larger distribution of their venom. This behavior increases the probability that at least one eye of the aggressor is hit. Electronic Supplementary Material Supplementary material is available for this article at     

Energy use and management of energy reserves in hatchling turtles (Chrysemys picta) exposed to variable winter conditions

The painted turtle (Chrysemys picta) is an especially useful organism in the study of metabolic regulation during dormancy because it is sustained by finite energy reserves from hatching until emerging from its nest, about nine months later. In this study we subjected overwintering C. picta hatchlings to 4, 10, or 15 °C, temperatures simulating cold, mild, and warm winters, respectively, to investigate how various energy reserves are impacted by differential metabolic demands. An energy budget based on seasonal changes in caloric content showed that these turtles consumed an average of 0.39, 0.75, or 1.21 kJ g⁻¹, respectively, during the 6-month period of simulated hibernation. These estimates of energy use agreed reasonably well with estimates based solely on respirometric data. Unexpectedly, turtles in autumn contained little residual yolk, none of which was consumed by turtles in the cold- and mild-winter groups, this finding contradicting the widely held belief that residual yolk plays an important, direct role in the survival of turtles that overwinter inside their natal nest. By contrast, a marked reduction in dry mass of both liver and carcass attested to their importance in fueling metabolism and, indeed, catabolism of substrates from these components accounted for 31–52 and 35–63%, respectively, of the energetic cost of overwintering. The greater dependence on carcass reserves and relatively poor physiological condition of turtles in the mild- and warm-winter groups implies that metabolic demands imposed by high environmental temperatures would likely constrain post-emergence fitness.