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PubMed2005

Rate of chromosome changes and speciation in reptiles.

The chromosome changing rate (i.e. the number of chromosome rearrangements per million years) was studied in 1,329 reptile species in order to evaluate the karyological evolutionary trend and the existence of possible correlations between chromosome mutations and some aspects of the evolution of this class. The results obtained highlight the existence of a general direct correlation between chromosome changing rate and number of living species, although different trends can be observed in the different orders and suborders. In turtles, the separation of pleurodires from cryptodires was accompanied by a considerable karyological diversification. Among pleurodires, the evolution of the Chelidae and Pelomedusidae was also characterised by chromosome variation, while in cryptodires a marked karyological homogeneity is observed between and within infra-orders. Similarly there is no correlation between changing rate and species number in crocodiles, where the evolution of the families and genera has entailed few chromosome mutations. Chromosome variability was greater in lizards and snakes. In the formers variations in chromosome changing rate accompanied the separation of the infra-orders and the evolution of most of the families and of some genera. The origin of snakes has also been accompanied by a marked karyological diversification, while the subsequent evolution of the infra-orders and families has entailed a high level of chromosome variability only in colubroids. The karyological evolution in reptiles generally entailed a progressive reduction in chromosome changing rate, albeit with differences in the diverse orders and suborders. This trend seems to be consistent with the "canalization model" as originally proposed by Bickham and Baker in [Bickham, J.W. & R J. Baker, 1979. Bull. Carnegie Mus. Nat. Hist. 13: 70-84.] However, several inconsistencies have been found excluding that in this class the ultimate goal of chromosome variations was the achievement of a so-called "optimum karyotype'' as suggested by the above-mentioned theory. Other mechanisms could underpin chromosome variability in Reptiles. Among them a genomic composition more or less favourable to promoting chromosome rearrangements and factors favouring the fixation of a mutant karyotype in condition of homozygosis. Turtles and crocodiles would have a genome characterised by large chromosomes and a low level of chromosome compartmentalisation limiting the recombination and the frequency of rearrangements. A low rate of chromosome variability modifying little if at all the gene linkage groups would have favoured a conservative evolutionary strategy. In the course of evolution, lizards and snakes could have achieved a genome characterised by smaller chromosomes and a higher level of compartmentalisation. This would have raised the frequency of recombination and consequently an evolutionary strategy promoting a higher degree of variability and a greater level of speciation.

Animals↗
PubMed2006

Reptile freeze tolerance: metabolism and gene expression.

Terrestrially hibernating reptiles that live in seasonally cold climates need effective strategies of cold hardiness to survive the winter. Use of thermally buffered hibernacula is very important but when exposure to temperatures below 0 degrees C cannot be avoided, either freeze avoidance (supercooling) or freeze tolerance strategies can be employed, sometimes by the same species depending on environmental conditions. Several reptile species display ecologically relevant freeze tolerance, surviving for extended times with 50% or more of their total body water frozen. The use of colligative cryoprotectants by reptiles is poorly developed but metabolic and enzymatic adaptations providing anoxia tolerance and antioxidant defense are important aids to freezing survival. New studies using DNA array screening are examining the role of freeze-responsive gene expression. Three categories of freeze responsive genes have been identified from recent screenings of liver and heart from freeze-exposed (5h post-nucleation at -2.5 degrees C) hatchling painted turtles, Chrysemys picta marginata. These genes encode (a) proteins involved in iron binding, (b) enzymes of antioxidant defense, and (c) serine protease inhibitors. The same genes were up-regulated by anoxia exposure (4 h of N2 gas exposure at 5 degrees C) of the hatchlings which suggests that these defenses for freeze tolerance are aimed at counteracting the injurious effects of the ischemia imposed by plasma freezing.

Animals↗
PubMed2005

Reptile virology.

Reptiles are hosts to diverse viral infections. This article reviews the viruses that are known to infect reptiles and discusses associated pathology, available diagnostic methods, and management techniques for the reptile clinician.

Animals↗
PubMed2006

Local control of pulmonary blood flow and lung structure in reptiles: implications for ventilation perfusion matching.

Lung structure of reptiles is very diverse ranging from single chambered lungs with a simple structure to more complex and multi-chambered lungs. Increased structural complexity resulted from the evolution of smaller gas exchange units and larger surface area, which increases the pulmonary diffusive capacity for O(2). However, increased structural complexity probably also increases the possibilities for ventilation-perfusion (V /Q ) heterogeneity, which exerts significant constraints on gas exchange. In most reptiles, the ventricle is anatomically and functionally undivided so blood pressures are equal in the systemic and pulmonary circulations. In these species, blood flow distribution between pulmonary and systemic circulations are primarily determined by pulmonary and systemic vascular resistances. Thus, increased pulmonary resistance lowers pulmonary blood flow through increasing cardiac right-to-left shunt decreasing systemic oxygen levels. It has been proposed that local mechanisms regulating pulmonary blood flow are more pronounced in reptiles with complex lungs as they are more prone to V /Q heterogeneity. However, local control of pulmonary blood flow has also been suggested to primarily exist when hearts are functionally divided because altered pulmonary vascular resistance does not affect cardiac shunt patterns. Data suggest that, while there seems to be a general trend of increased local regulation of pulmonary blood flow in species with structurally complex lungs and divided hearts, it is also possible that other factors, such as breathing pattern, have been important for the evolutionary development of local regulatory mechanisms in the lungs.

Animals↗
PubMed1997

Lithium secretion in kidneys of amphibians and reptiles under hydrated conditions.

Renal lithium transport was studied at different hydration levels in five species of anuran amphibians (Bufo bufo, B. danatensis, B. viridis, Rana ridibunda, and R. temporaria), two species of urodeles (Triturus vulgaris and T. cristatus) and four species of reptiles (lizards Eremias multiocellata, Lacerta vivipara, Trapelus sanguinolentus, and Teratoscincus scincus). Under dehydration conditions, Li+ was reabsorbed in the kidneys of amphibians ans reptiles, but to a lesser degree than in mammalian kidneys: the ratio of lithium clearance (CLi) to glomerular filtration rate (GFR)--fractional lithium excretion--in dehydrated animals was in the range 0.5-0.8. The transition to the hydrated state resulted in a cessation of net renal lithium reabsorption. Under condition of high hydration, all the animals studied, except for urodeles, showed net renal secretion of Li+, i.e., CLi exceeded GFR. The ratio CLi/GFR was 1.2-1.3 in hydrated anurans and 1.7-2.3 in hydrated lizards. In urodeles, this ratio was approximately unity. It is suggested that renal lithium secretion in hydrated amphibians and reptiles reflects fluid secretion in the proximal tubule, which is additional to the glomerular filtration mechanism of fluid delivery to nephron under water loading.

Amphibians↗
PubMed2002

The proliferative ventricular zone in adult vertebrates: a comparative study using reptiles, birds, and mammals.

Although evidence accumulated during the last decades has advanced our understanding of adult neurogenesis in the vertebrate brain, many aspects of this intriguing phenomenon remain controversial. Here we review the organization and cellular composition of the ventricular wall of reptiles, birds, and mammals in an effort to identify differences and commonalities among these vertebrate classes. Three major cell types have been identified in the ventricular zone of reptiles and birds: migrating (Type A) cells, radial glial (Type B) cells, and ependymal (Type E) cells. Cells similar anatomically and functionally to Types A, B, and E have also been described in the ventricular wall of mammals, which contains an additional cell type (Type C) not found in reptiles or birds. The bulk of the evidence points to a role of Type B cells as primary neural precursors (stem cells) in the three classes of living amniotic vertebrates. This finding may have implications for the development of strategies for the possible treatment of human neurological disorders.

Animals↗
PubMed2002

Diagnosis and management of reptile orthopedic injuries.

As veterinarians expand their understanding of the specific husbandry requirements for captive reptiles, nutritionally associated orthopedic injuries should decrease. Orthopedic injuries in wild reptiles, however, will continue to increase as new infrastructure encroaches on the habitats of these animals. Research should be pursued that focuses on improving our understanding of pain management in reptiles, on developing techniques to expedite bone healing, and on creating new orthopedic techniques that provide rigid stabilization without the use of temperature-sensitive materials.

Animals↗
PubMed2001

Clinical aspects of reptile behavior.

At first glance, the abstract world of reptile ethology may seem remote to clinicians dealing with the health and disease of captive animals. By delving a little deeper, however, veterinarians can learn to appreciate the reasons for certain behaviors and actually use these behaviors as indicators of various biologic states. Close scrutiny of subtle changes in behavior can further help assess reptile well-being and judge captive welfare. In the future, it is hoped that improved ethologic understanding will result in behavioral enrichment for reptiles, as is already promoted for many nondomestic mammals and birds.

Animals↗
PubMed2001

Dermatology of reptiles: a clinical approach to diagnosis and treatment.

As herpetoculture becomes more commonly practiced, many of the dermatologic problems discussed in this article will be encountered less frequently. Many of the problems result from a general lack of knowledge regarding proper nutrition, husbandry, and the overall needs of reptiles within a captive environment. As reptiles become more a part of the mainstream pet population, information about their care will undoubtedly become more accessible, and as more captive-raised reptiles become available in the pet trade, many of the dermatoses currently associated with wild-caught animals will become less common.

Animal Husbandry↗
PubMed2000

Nonreproductive surgery in reptiles.

As reptiles have gained popularity as pets, veterinarians are more frequently called on to perform surgical procedures on these pets. Veterinarians must have a basic understanding of the anatomic and physiologic differences between reptilian and mammalian companion animals. This article reviews some basic points about reptilian anatomy and physiology that are important to consider when performing surgery on reptilian patients. This article covers approaches to the coelomic cavity in the different groups of reptiles and some basic concepts regarding surgery on different, nonreproductive systems in these reptiles.

Animal Diseases↗
PubMed2000

Reproductive surgery in reptiles.

Reptiles are commonly presented to veterinarians for reproductive problems. Often, these problems require surgical intervention. This article discusses some of the major causes of dystocia in reptiles and describes the surgical treatment of the female reproductive tract, including ovariectomy, ovariosalpingohysterectomy, and prolapse of the shell gland. Descriptions of surgical intervention in male reptiles include orchidectomy and paraphimosis.

Animal Diseases↗
PubMed2002

Energy and nutrient utilisation by embryonic reptiles.

Most reptiles are oviparous, with the developing embryos relying on the contents of the yolk to sustain development until hatching (lecithotrophy). The yolk is composed primarily of lipid and protein, which act as an energy source and the essential components to build embryonic tissue. Nevertheless, yolk and the resulting embryos contain many other nutrients, including inorganic ions, vitamins, carotenoids, water and hormones. Apart from water and oxygen, which may be taken up by eggs, and some inorganic ions that can come from the eggshell or even from outside the egg, everything required by the embryo must be in the egg when it is laid. Approximately 20% of squamate reptiles are viviparous, exhibiting a variety of placental complexities. Species with complex placentae have reduced yolk volumes, with the mother augmenting embryonic nutrition by provision across the placenta (placentotrophy). Despite assumed advantages of placentotrophy, only 5 out of approximately 100 lineages of viviparous squamates exhibit substantial placentotrophy. This paper reviews available and recent information on the yolk contents of a variety of squamate reptiles to ask the question, how are nutrients transported from the yolk to the embryo or across the placenta? Although, current available data suggest that, in broad terms, yolk is taken up by embryos without discrimination of the nutrients, there are some apparent exceptions, including the very long chain polyunsaturated fatty acids. In addition, fundamental differences in the patterns of energy utilisation in lizards and snakes suggest fundamental differences in lipid profiles in these taxa, which appear to reflect the differences between placentotrophic and lecithotrophic viviparous lizards.

Animals↗
PubMed2003

Do mammals, birds, reptiles and fish have similar nitrogen conserving systems?

Comparative physiological studies are a powerful tool for revealing common animal adaptations. Amino acid catabolism produces ammonia which is detoxified through the synthesis of urea (mammals, some fish), uric acid (birds), or urea and uric acid (reptiles). In mammalian herbivores and omnivores, urea nitrogen is salvaged by a series of steps involving urea transfer into the intestine, microbial mediated urea hydrolysis with synthesis of amino acids utilizing the liberated ammonia and transfer of the amino acids back to the host. A similar series of steps occur in omnivorous/granivorous and herbivorous birds, although in this case urine, containing uric acid, is refluxed directly into the intestine where microbes degrade the uric acid and utilize the liberated ammonia for amino acid synthesis. These amino acids are transferred back to the host. In reptiles and ureotelic fish not all of these steps have been experimentally confirmed. Reptiles like birds, reflux urine into the intestine where it is exposed to the microflora. However, the capacity of these microbes to breakdown the uric acid and urea and utilize ammonia for amino acid synthesis has not been documented. Ureotelic fish transfer urea into the intestine where urease (presumably of bacterial origin) hydrolyzes the urea. However, the amino acid synthesizing capacity of the intestinal microflora has not been studied. The series of steps, as outlined, would define the prevailing nitrogen conservation system for herbivores and omnivores at least. However, it would appear that some animals, in particular the fruit-eating bat and perhaps the fruit-eating bird, may have evolved alternative, as yet uncharacterized, adaptations to a very limited nitrogen intake.

Ammonia↗
PubMed1997

Sex differences in the nervous system of reptiles.

1. The study of sex differences in the brain and behavior of reptiles presents an excellent opportunity both to discern general principles of sexual differentiation in the nervous system and to explore the evolutionary history of this process in amniote vertebrates. 2. Findings in several reptiles suggest that some sex differences found in mammals and birds are conserved while others are not. Conserved features include areas in the limbic forebrain involved in the regulation of social and sexual behaviors. As in mammals and birds, it is rare to find differences in the distribution of sex steroid concentrating neurons in reptiles but common to find differences in the distribution of the various steroid hormone receptors and in their regulation. 3. This research has revealed that differences in social and sexual behavior are reflected better by the activity, not by the size, of hormone-sensitive limbic areas. 4. Finally, species differences in plasma levels of sex hormones are paralleled by differences in behavioral sensitivity to these hormones as well as by differences in the regulation of genes coding for steroid hormone receptors.

Animals↗
PubMedDate not supplied

Evidence of H beta 58, a gene involved in mammalian placental development, in the three-toed skink, Chalcides chalcides (Squamata: Scincidae), a viviparous placentotrophic reptile.

The H beta 58 gene, whose disruption in mice causes reabsorption of the embryo at 9.5 days post-conception, is believed to be essential for development of the placenta. Although the H beta 58 gene is well conserved in some Amniota, nothing is known about its presence in reptiles, some species of which have developed a chorioallantoic placenta. In this work, we investigated the expression of H beta 58 mRNA and protein in the three-toed skink, Chalcides chalcides. H beta 58 protein expression was found in the uterine epithelium beginning from the peri-ovulatory stage. However, it increased strongly at the moment of placental formation, when a high level of expression of mRNA and protein was also observed in the extra-embryonic membranes. The expression of H beta 58 mRNA and protein was maintained, although to a lesser degree, in the placenta during late pregnancy. It was also present in the early embryo. Finally, cloning and sequencing of a gene fragment revealed strong homology of the reptile gene with that of mammals. The high degree of conservation of the gene in amniote vertebrates and its presence in a viviparous squamate reptile (as in mammals) indicates an important role of this gene in the chorioallantoic placenta formation and development.

Allantois↗
PubMedDate not supplied

Growth and metabolism in the embryonic white-spotted bamboo shark, Chiloscyllium plagiosum: comparison with embryonic birds and reptiles.

Birds and reptiles have been important models for studying the energetics of embryonic development. Studies on these groups reveal three metabolic patterns: an exponential increase in metabolism with embryo age, a sigmoidal increase with age, or a sigmoidal increase followed by a decrease before hatching. Models developed to explain avian metabolic patterns and developmental costs partition total costs between growth and maintenance. To test the generality of these models, we examined embryonic energetics of the oviparous white-spotted bamboo shark Chiloscyllium plagiosum. Oviparous sharks must actively ventilate during development, which could increase their development costs relative to birds and reptiles. Our results demonstrated that bamboo shark embryos have a peaked metabolic pattern and sigmoidal increase in body mass similar to ratites, crocodilians, and some turtles. The total cost of development was higher in bamboo sharks than in reptiles and many birds. However, calculations reveal that the high cost of bamboo shark development can be explained by the relatively long incubation time rather than the additional cost of muscular movement. Finally, an avian model can reasonably describe shark embryonic metabolism, suggesting that movement costs do not significantly alter the metabolic pattern during development.

Animals↗
PubMed2004

Salmonella diversity associated with wild reptiles and amphibians in Spain.

During the spring and summer of 2001, faeces from 166 wild reptiles (94 individuals) and amphibians (72 individuals) from 21 different species found in central Spain were examined for the presence of Salmonella. Thirty-nine reptiles (41.5%) yielded 48 Salmonella isolates, whereas all the amphibians examined were negative. Subspecies Salmonella enterica enterica (I) accounted for up to 50% of isolates. Fourteen isolates (29.2%) belonged to subspecies diarizonae (IIIb), six isolates (12.5%) to subspecies salamae (II), and four isolates (8.3%) to subspecies arizonae (IIIa). Twenty-seven different serotypes were identified. Serotypes Anatum (12.5%), Herzliya (8.3%), Abony, 18:l,v:z, 9,12:z29:1,5 and 38:z10:z53 (6.2%/each) were the most frequently isolated. A high percentage (39.6%) of isolates belonged to serotypes previously associated with environmental sources. Also, 37.5% of isolates belonged to serotypes which had been related to human cases of salmonellosis. From these data, it is concluded that wild reptiles, but apparently not amphibians, may represent an important reservoir of Salmonella in nature and have potential implications for public health.

Amphibians↗
PubMed1988

A fossil reptile embryo from the Middle Triassic of the Alps.

The first nothosaur (Neusticosaurus sp.) embryo, one of the very few fossil embryos known, provides a rare glimpse at reproduction in extinct reptiles. The specimen from the southern Alpine Middle Triassic (about 230 million years ago) was recognized as an embryo in comparison with an exceptionally large and well-understood sample of juvenile and sexed adult Neusticosaurus sp. The skeleton shows many embryonic features and may well be the smallest fossil reptile known (body length 51 millimeters). It reached only 22% of mean adult length whereas modern reptiles of this size do not hatch before they reach about 30% of mean adult length. The question of ovipary versus vivipary in pachypleurosaurs is discussed in light of the embryo.

Animals↗