Assessment of the role of sutures in a lizard skull: a computer modelling study

Sutures form an integral part of the functioning skull, but their role has long been debated among vertebrate morphologists and palaeontologists. Furthermore, the relationship between typical skull sutures, and those involved in cranial kinesis, is poorly understood. In a series of computational modelling studies, complex loading conditions obtained through multibody dynamics analysis were imposed on a finite element model of the skull of Uromastyx hardwickii, an akinetic herbivorous lizard. A finite element analysis (FEA) of a skull with no sutures revealed higher patterns of strain in regions where cranial sutures are located in the skull. From these findings, FEAs were performed on skulls with sutures (individual and groups of sutures) to investigate their role and function more thoroughly. Our results showed that individual sutures relieved strain locally, but only at the expense of elevated strain in other regions of the skull. These findings provide an insight into the behaviour of sutures and show how they are adapted to work together to distribute strain around the skull. Premature fusion of one suture could therefore lead to increased abnormal loading on other regions of the skull causing irregular bone growth and deformities. This detailed investigation also revealed that the frontal-parietal suture of the Uromastyx skull played a substantial role in relieving strain compared with the other sutures. This raises questions about the original role of mesokinesis in squamate evolution.     

Characterization of hemoglobin from the lizard Uromastix hardwickii

Hemoglobin from the tropic lizard Uromastix hardwickii was isolated. Chain separations were studied, and the whole carboxymethylated globin was cleaved with trypsin. Peptides were pre-fractionated by exclusion chromatography and finally purified by reversed phase high-performance liquid chromatography. Amino acid sequence analysis permitted ordering of peptides in alpha- and beta-chains by homology with known structures in other hemoglobins. Results show large structural variations (about 50% homology between Uromastix and viper alpha-chains) and suggest chain heterogeneity with the presence of at least two types of both the alpha- and beta-chains in the preparations.     

Microbial digestion in the herbivorous lizard Uromastyx aegyptius (Agamidae)

The utilization of a diet rich in plant cell walls was studied in a large, desert-dwelling, herbivorous lizard, Uromastyx aegyptius (Agamidae). The diet eaten by U. aegyptius in spring in the 'Arava Valley, Israel, consisted almost entirely of leaves and fruits of short-lived annual plant species. The leaves contained only moderate levels of fibre compared with grasses and tree leaves, but those fruits eaten were markedly higher in fibre and lignin. All items had notably high contents of ash.
Following oral doses of [¹⁴C] cellulose, ¹⁴CO₂ was detected in respired air from U. aegyptius , demonstrating that the cellulose was digested and that the lizards gained oxidative energy from cellulose degradation. The hind gut was the principal site of microbial activity and the apparent digestibility of the cell-wall fraction was 69%. Similarly, the caecum/proximal colon had the highest concentrations of SCFA (76–120 mM).
The mean rate of SCFA production at 40 C in vitro was 31 mmol/1 h^-1. Assuming that this is representative of daily production rate, 69 kJ/kg d^-1 would be made available to the animal. This is 47% of the mean digestible energy intake estimated in free-living animals. Microbial fermentation contributes an important part of the energy budget of U. aegyptius but the effects of variation in body temperature on digestion and fermentation need further consideration.     

The dentition and dental tissues of the agamid lizard, Uromastyx

The dentition of Uromastyx hardwicki was examined in a series of carefully prepared dry skulls and was found to be very different from that of other agamid lizards. The anatomy of the dentition undergoes great changes from the time of hatching to advanced age, but no evidence of tooth replacement could be found. Extension of the tooth rows by addition of larger teeth posteriorly, together with elongation of the premaxilla, and a characteristic pattern of wear are responsible for the condition seen in aged specimens.
The structure of the dental tissues was investigated by means of a variety of histological techniques including scanning electron microscopy and it is established that the enamel has prismatic structure like that of mammalian enamel. The mode of formation of enamel with and without prisms is described and the occurrence and significance of prismatic structure in reptilian dental enamel discussed.     

Gluconeogenesis in the kidney and liver slices of a lizard, Uromastix hardwickii

1. The liver and kidney of the lizard Uromastix hardwickii have much higher contents of carbohydrate than have been reported for the corresponding rat tissues. Most of this carbohydrate still remains in the tissue even after a long preincubation. 2. Kidney slices of this lizard release both glucose and other carbohydrates into the medium. Hence glucose release alone, as demonstrated for rats, cannot be used as a good criterion of gluconeogenesis in this lizard. Moreover, the results obtained by glucose release did not agree with those in which the total carbohydrate was estimated in the slice and medium. 3. l-Glutamate, l-aspartate, dl-valine, l-proline, l-cysteine, l-lactate and succinate stimulated gluconeogenesis in the kidney slices, whereas citrate, l-alanine, l-serine, glycine, l-arginine and l-leucine did not. In liver slices only l-glutamate increased gluconeogenesis. 4. New carbohydrate formation in the kidney and liver slices after incubation with various substrates indicated that gluconeogenesis as well as the amino acid metabolism in this animal may be somewhat different from that of mammals.     

Immunolocalization of hepatic estrogen and progesterone receptors in the female lizard Uromastyx acanthinura

The hormonal regulation of hepatic synthesis of vitellogenin during the annual reproductive cycle was performed for the first time in the deserticole, oviparous, diurnal and herbivorous Uromastyx acanthinura, a lizard belonging to the Agamidae family. In order to elucidate what kind of estrogen receptor is involved in this process, an immunohistochemical study was performed. Changes were obtained in the labeling and cellular distribution of the estrogen and progesterone receptors according to the period of the reproductive cycle and the experimental administration of 17β-estradiol. Only the ERβ subtype was present; it was found in all phases of the cycle with a variable localization: nuclear and cytosolic during vitellogenesis, mainly cytosolic in the female with egg retention (luteal phase) and strictly cytosolic in females at sexual rest. The progesterone receptors were present only at the luteal phase and during sexual rest and disappeared completely from females after 17β-estradiol treatment in sexual rest. Our data suggested that mediation of action of the 17β-estradiol in the vitellogenin synthesis in the lizard U. acanthinura occured via ERβ. PRA and PRB could both be necessary for the negative effect of progesterone on the hepatic synthesis of vitellogenin.     

The Harderian gland of the Dhub lizard Uromastyx microlepis of the Kuwaiti desert: an ultrastructural approach

Harderian glands exist in the orbits of most terrestrial vertebrates. The basic function of the gland is the lubrication of the eye. The present study was carried out to shed some light on the ultrastructure of the still enigmatic Harderian gland of the lizard Uromastyx microlepis, a common species in Kuwait and other Gulf areas. The Harderian gland of Uromastyx microlepis is well developed, relatively large in size and lingual in shape. The epithelial cells of the anterior part of the gland are characterized by the presence of membrane bound granules of almost homogeneous consistency. These secretory granules are gathered in compartments and separated by membranes and stacks of granular endoplasmic reticulum (GER). Most of the lumina were empty. Moderate amounts of GER, free ribosomes and pleiomorphic mitochondria were observed in the perinuclear area of the epithelial cells. The medial and caudal parts of the gland were rich in special secretory granules, GER, free ribosomes and pleiomorphic mitochondria. The anterior part of the gland could represent the future lacrimal gland of mammals. A network of myoepithelial cells was recognized around the gland tubules. While no melanocytes or lymphocytes were observed in the scarce interstitial tissue, macrophages, that might have an immune function in the gland, were observed.     

Immunocytochemical localization and ultrastructural study of gonadotroph cells in the female desert lizard Uromastyx acanthinura

The pars distalis from the pituitary gland of adult female desert lizards (Uromastyx acanthinura), captured during vitellogenesis (late may) and hivernal period, was studied with immunocytochemical methods using specific antisera against human FSH (hFSH) and LH (hLH). The immunostaining with anti-hLH and anti-hFSH allowed the identification of only FSH-like containing cells. The FSH-like immunoreactive cells were affected differently by a physiological stage and showed some heterogenous cytological characteristics. During vitellogenesis, four aspects of rostral FSH-like immunoreactive cells could be recognized. The expression of FSH-like in mainly immunoreactive cells was parallel to an intense synthetic activity and to the presence of ultrastructural features indicating an intense release of the hormone. This release was considerably altered in winter, the immunoreactive cells stored an important amount of secretion granules which increased in size and undergo a crinophagic process.     

Effects of temperature and hypercapnia on ventilation and breathing pattern in the lizard Uromastyx aegyptius microlepis

In most reptiles, the ventilatory response to hypercapnia consists of large increases in tidal volume (V(T)), whereas the effects on breathing frequency (f(R)) are more variable. The increased V(T) seems to arise from direct inhibition of pulmonary stretch receptors. Most reptiles also exhibit a transitory increase in ventilation upon removal of CO(2) and this post-hypercapnic hyperpnea may consist of changes in both V(T) and f(R). While it is well established that increased body temperature augments the ventilatory response to hypercapnia, the effects of temperature on the post-hypercapnic hyperpnea is less described. In the present study, we characterise the ventilatory response of the agamid lizard Uromastyx aegyptius to hypercapnia and upon the return to air at 25 and 35 degrees C. At both temperatures, hypercapnia caused large increases in V(T) and small reductions in f(R), that were most pronounced at the higher temperature. The post-hypercapnic hyperpnea, which mainly consisted of increased f(R), was numerically larger at 35 compared to 25 degrees C. However, when expressed as a proportion of the levels of ventilation reached during steady-state hypercapnia, the post-hypercapnic hyperpnea was largest at 25 degrees C. Some individuals exhibited buccal pumping where each expiratory thoracic breath was followed by numerous small forced inhalations caused by contractions of the buccal cavity. This breathing pattern was most pronounced during severe hypercapnia and particularly evident during the post-hypercapnic hyperpnea.     

Immunolocalization of estrogens and progesterone receptors within the ovary of the lizard Uromastyx acanthinura from vitellogenesis to rest season

The sites of action and the physiological role of estrogens and progesterone in the ovary are poorly understood in Reptiles. We have undertaken a systematic study of the immunoexpression of classical oestrogen receptor (ER or ERalpha) and progesterone receptor (PR) in the female lizard during the reproductive cycle. During vitellogenesis, ER was not expressed in vitellogenic follicles whereas PR was weakly detected in the nucleus of some follicular cells and well expressed in the internal theca cells. The follicular and theca cells were immunopositive for ER in the previtellogenic follicles, the signal in both was cytosolic. PR was strongly expressed in the follicular cells, the signal was localised in the nucleus. In the post-reproductive period, ER was detected in the previtellogenic follicles in the same manner as in the breeding period. The staining for PR was expressed in both the nucleus and cytoplasm of follicular cells and theca cells. In the sexual rest, the previtellogenic follicles were all negative for ER and PR immunoexpression. These findings suggest that the main action of estrogens in the ovary is not mediated by ER. The expression of cytosolic PR only in the post-reproduction period, at the same time at the progesterone synthesis, supports the hypothesis which stipulates an exclusive nuclear localization in the absence of progesterone.     

Effect of hypocalcemic and hypercalcemic substances on the parathyroid histology of the lizard, Uromastix hardwickii (Gray).

The effects of hypocalcemic and hypercalcemic substance on activity of the parathyroid and plasma calcium and phosphorus levels in the lizard, Uromastix hardwickii are described. The cellular hypertrophy and degranulation of cytoplasm in the parathyroid cells along with decrease in plasma calcium level appeared after sodium citrate and ethylenediaminetetraacetate (EDTA) treatment. On the other hand, degenerative changes are observed after calcium chloride treatment. It is suggested that the secretion of parathyroid is regulated by the circulating blood calcium level.     

Morphological Variations,Distribution and Population Estimation of Indian Spiny Tailed Lizard (Uromastyx hardwickii Gray, 1827) from District Bahawalnagar,Punjab, Pakistan

This study was conducted in selected sites of District Bahawalnagar namely, Shaheed Chowk, Chak40/F, Chak 163/7R and Fareedkot Tiba between March 2019 and Augus...     

A new Haemocystidium (Apicomplexa: Plasmodiidae) species of the dhub lizard, Uromastyx aegyptia microlepis , in Abu Dhabi, distinguished by the absence of pigment

The spiny-tailed lizard, Uromastyx aegyptia microlepis , in Abu Dhabi is parasitized by Haemocystidium apigmentada n. sp., and 2 species of Hepatozoon . The elongate gametocytes of H. apigmentada are 13-19 × 6-9 μm, with length × width (LW) 90-133 μm(2), and L/W ratio 1.56-3.17. Gametocyte dimensions do not differ by sex. Gametocytes are unpigmented. Hepatozoon species 1 has gamonts with a consistently terminal nucleus, with dimensions of 13-16 × 4.5-7 μm, LW of 58-104 μm(2), and L/W ratio of 2.00-3.22. Hepatozoon species 2 gamonts have a broad nucleus at the midbody, and dimensions of 13-15.5 × 5-7 μm, LW of 71-109 μm(2), and L/W ratio of 1.93-3.00.     

The development of the trigeminal jaw adductor musculature and associated skull elements in the lizard Podarcis sicula

The ontogenetic development of the jaw adductor musculature in Podarcis sicula (Raftnesque) is described in detail and related to patterns of ossification in associated skull elements. It was found that the coronoid bone ossifies in continuity with the developing bodenaponeurosis, whereas the elements of the upper temporal arcade ossify prior to (and seemingly independently of) the realization of an attachment of the developing jaw adductors.
Various aspects of the development of the jaw adductors are discussed in the light of theoretical claims concerning conflicting models of ontogeny, as is the role of ontogenetic studies in the determination of character polarity. It is concluded that the present study supports the model of epigenetic development, and that ontogeny alone is insufficient for the assessment of character polarity. Instead, ontogeny must be interpreted in the context of phylogenetic hypotheses.     

Fractal analysis of the Orce skull sutures

Methods of fractal geometry (Mandelbrot, 1983) are used here to analyse the relative complexity of the sagittal and lambdoid sutures visible in the skull fragment formed by parts of an occipital squame and parietals found in a sealed deposit at the early Lower Pleistocene site of Venta Micena (Orce, Granada, Spain), generally regarded as human bone but occasionally suggested as belonging to an equid. For comparison with the fossil, corresponding sutures of various primates (hominids, pongids and cercopithecids) and two other groups of mammals (equids and ruminants) were analysed using the computer program FRACTAL-D (Slice, 1989) in order to determine their fractal dimensions as a measure of differential sutural design complexity. The results show that the fractal dimension of the Venta Micena skull sutures lies within the range of variation for infant specimens of both modern and Plio-Pleistocene hominids. Sutural complexity in young pongids and cercopithecids overlaps the range of fractal dimensions found in hominids, whereas values obtained from equids and ruminants are significantly greater than those for all the primates analysed here. Therefore, in terms of fractal dimension measures of relative complexity, the sutures preserved in the Venta Micena fossil could not have belonged to an equid (pace Agusti & Moyà-Sola, 1987); rather, its fractal dimension is consistent with the attribution of the fossil to an infant of Homo sp.     

Rigid-body oscillations of alpha-helices: implications for protein thermal stability

A quasi-continuity model protein consisting of two alpha-helices undergoing rigid-body torsional oscillations demonstrates that factors stabilizing the model protein, such as increased helix rigidity and hydrophobicity, are the same factors that stabilize thermophilic proteins relative to their mesophilic analogs. The model predicts oscillatory motions with frequencies in the microwave (10(10) Hz) range. These oscillations decrease in frequency with increasing helix rigidity because of compensating increases in the force constant and moment of inertia, thus explaining the retention of activity in the more rigid thermophilic enzymes. Implications for protein design, based on the predictions of the model, are discussed.