The endocrine pancreas of Alligator mississippiensis

Summary Immunocytochemical methods for light and electron microscopy were used to demonstrate the regulatory peptides present in the endocrine pancreas of thealligator, Alligator mississippiensis.The peptides studied included insulin, glucagon (pancreatic and enteric), somatostatin, pancreatic polypeptide (avian, bovine and human), vasoactive intestinal polypeptide, substance P, metenkephalin, -endorphin, C-terminal gastrin/CCK and gastric inhibitory polypeptide. Endocrine cells were detected using antisera to insulin, pancreatic glucagon, somatostatin and avian pancreatic polypeptide, whereas peptidergic nerves were stained with antisera to vasoactive intestinal polypeptide. All other antisera were unreactive in the alligator pancreas. The peptide-containing structures were identified ultrastructurally by both the semithin/thin and immuno-gold methods. The results showed that five of the regulatory peptides commonly detected in the mammalian pancreas were immunologically recognisable in the alligator. In addition, the ultrastructural appearance of the peptide-containing cells was clearly distinct from that reported in mammals.     

Social Displays of the American Alligator (Alligator mississippiensis)

Adult alligators perform two conspicuous social displays, bellowsand headslaps. Both of these behaviors are performed from a"head oblique tail arched" (HOTA) posture. Bellow displays,by both males and females, involve the production of a loud,roaring vocalization. Male alligators also produce a infrasonicsignal, termed subaudible vibrations, just prior to the audiblebellow. Bellowing occurs throughout the year but is most frequentduring the courting season, when alligators bellow daily inchoruses. Chorus length appears to be correlated with the sizeof the adult population. Chorusing is frequently initiated byfemales but seems to be perpetuated by male alligators. Bellowingmay serve to attract alligators of the opposite sex and possiblyto space out animals of the same sex. The headslap display is an assertion display consisting of eightcomponent behavioral acts: the elevated posture, HOTA posture,subaudible vibrations, headslap, jawclap, growl, inflated posture,and tail wag. Each act component is variable in presence andintensity producing a highly variable, graded signal. The alligatortypically remains motionless in the HOTA posture for about 16sec before executing the headslap/jawclap acts. The headslapdisplay involves a rapid clapping shut of the jaws as the undersurfaceof the head is slapped against the water surface. Headslappingis most common in early morning and afternoon hours. Analysisof 1,050 headslap displays by 91 known individuals indicatesthat 94.5% of the observed displays were performed by males.Headslap displays are generally performed from typical displaysites which the alligator seeks out prior to the display. Responsesto headslap displays include headslapping by others, lunges,approaches, and bellow growling. The headslap display functionsas a declaration of presence. A musky odor is commonly detected in association with both ofthese social displays, suggesting a possibly important, butlittle understood, pheromonal component of these behaviors. The displays both involve complex signals including visual,auditory, olfactory and possibly tactile channels of communication.Most of the behaviors described are shared with many other speciesof crocodilians.     

Femoral dimensions and mid-thigh circumference in Alligator mississippiensis

The mid-thigh circumference of the intact hindlimb in Alligator mississippiensis is tightly correlated with transverse dimensions of the proximal and distal articular surfaces of the femur, and with minimum midshaft femoral circumference. Maximum diameter of the proximal articular end, width across the distal articular end, and midshaft circumference are the best femoral predictors of circumference of the intact thigh. Regression equations of mid-thigh circumference against these femoral dimensions can be used to estimate the transverse dimensions of the intact hindlimb in extinct crocodylian-like archosaurs.     

Differences in tissue-specific lipid composition between embryos of wild and captive breeding alligators (Alligator mississippiensis)

Fertile eggs obtained from alligators reared in captivity typically exhibit high rates of embryonic mortality. Also, the fatty acid composition of the yolk lipid of the captive eggs is markedly different from that observed in eggs from wild alligators, possibly as a result of differences in maternal diet in the two situations. The fatty acid compositions of tissue lipids during the embryonic development of wild and captive alligators were compared. The lipids of liver, adipose tissue and heart of the two types of embryo displayed fatty acid profiles which generally reflected the acyl compositions of the respective yolks. Thus the lipids from these tissues of the captive embryos contained markedly higher proportionate levels of linoleic and linolenic acids, lower levels of palmitoleic acid, and, in general, lower levels of docosahexaenoic acid and other C20 and C22 polyunsaturates, in comparison to the values for the wild embryos. In contrast, the fatty acid composition of the brain phosphoglycerides was very similar in the two types of embryo. Thus, at least in those embryos which had survived during the developmental period studied, the brain was able to maintain a relatively constant fatty acid composition, in spite of major differences between the wild and captive eggs in the proportions of the various fatty acids supplied from the yolk. It is suggested that a major cause of embryonic mortality in the captive embryos could be a failure to maintain an adequate level of docosahexaenoic acid in the developing brain.     

Iron withholding as an innate immune mechanism in the American alligator (Alligator mississippiensis)

Pathogenic microbes require Fe and Zn for growth and proliferation. Upon infection, microbes produce proteins, called sidephores, designed to strip serum divalent metals away from host proteins. Higher vertebrates respond to infection by increasing the expression of proteins that sequester serum iron away from bacteria. As a result, host plasma Fe levels decrease during the initial phases of infection. This study was conducted to determine if the American alligator, an ancient reptile, exhibits the same innate immune mechanism to protect against in vivo microbial proliferation. Intraperitoneal injection of juvenile captive alligators with bacterial lipopolysaccharide (LPS) resulted in a time-dependent decrease in plasma Fe, as determined by inductively coupled plasma emission spectroscopy. Plasma Fe levels decreased by 5.9, 10.6, and 18.6% relative to untreated control levels at 3, 6, and 12 hr post-injection, respectively, and remained decreased by 12.0% at 48 hr. Alligators injected with pyrogen-free saline did not exhibit statistically significant changes in plasma Fe concentrations at any time point observed. In contrast, serum Zn and Cu remained unchanged relative to untreated controls. To insure that the decreases in plasma Fe were not due to the repeated blood collections during the course of the kinetic study, another experiment was conducted in which plasma metals were measured at 24 hr post-injection. Once again, plasma Fe was reduced by 30.2%, whereas Zn and Cu did not exhibit appreciable changes. These results show that alligators exhibit low plasma Fe levels during an inflammatory response induced by bacterial lipopolysaccharide.     

Changes in femoral morphology during egg-laying in Alligator mississippiensis

Birds and many reptiles are egg-layers. Birds provide calcium for the formation of eggshells by resorbing medullary bone, which is laid down before ovulation. Turtles do not possess this mechanism and resorb structural bone to form eggshells. Femora from three groups of alligators (egg-laying females; quiescent, immature, or barren females; and males) were examined to determine if alligators, which are closely related to birds in evolution, resorb structural bone during the formation of eggshells as do turtles. Microradiographs of cross sections from femoral mid-shafts were analyzed for porosity, and the robusticity index of each femur was determined. Scanning electron micrographs of anorganic endosteal and periosteal femoral surfaces were analyzed to determine numbers of entrances of vascular canals, numbers of lacunae of osteoblasts, and types of femoral surfaces. Femora from egg-laying females were significantly less robust than those of other females or males, and sections of bone from the egg-layers were significantly more porous than those of the other groups. Scanning electron microscopy of anorganic femoral endosteal surfaces from egg-laying females revealed significantly more resorption areas when compared with males or non egg-laying females. Periosteal surfaces from egg-layers had significantly more resting and less bone-forming surface than those from the other groups. Results indicated that apposition of periosteal bone may have been reduced in egg-layers and that egg-laying alligators, like turtles, resorb endosteal structural bone, which may be used as a source of calcium for the formation of eggshells.     

Ultrastructure of the spermatozoon of the American Alligator,Alligator mississippiensis (Reptilia: Alligatoridae)

This study details the ultrastructure of the spermatozoa of the American Alligator, Alligator mississippiensis. American Alligator spermatozoa are filiform and slightly curved. The acrosome is tapered at its anterior end and surrounded by the acrosome vesicle and an underlying subacrosomal cone, which rests just cephalic to the nuclear rostrum. One endonuclear canal extends from the subacrosomal cone through the rostral nucleus and deep into the nuclear body. The neck region separates the nucleus and midpiece and houses the proximal centriole and pericentriolar material. The distal centriole extends through the midpiece and has 9 × 3 sets of peripheral microtubules with a central doublet pair within the axoneme that is surrounded by a dense sheath. The midpiece is composed of seven to nine rings of mitochondria, which have combinations of concentrically and septate cristae. The principal piece has a dense fibrous sheath that surrounds an axoneme with a 9 + 2 microtubule arrangement. The sheath becomes significantly reduced in size caudally within the principal piece and is completely missing from the endpiece. Dense peripheral fibers, especially those associated with microtubule doublets 3 and 8, penetrate into the anterior portion of the principal piece axoneme. The data reported here hypothesize that sperm morphology is highly conserved in Crocodylia; however, specific morphological differences can exist between species. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Dorsal galnds of Alligator mississippiensis: a histological and histochemical study

Several investigators have described in some crocodilians a row of round or oval organs, called dorsal glands, lying under scutes on each side of the dorsal midline. The function of these glands is unknown, but they are hypothesized to produce skin-conditioning secretions. We investigated the anatomy and histochemistry of the dorsal glands of adult American alligators ( Alligator mississippiensis ). Twenty to 22 pairs of glands containing a viscous, often black, material were observed lying from the mid-cervical to the anterior caudal regions in the axial musculature or on the inner surface of the dermis. The capsule of each gland consists of dense collagenous fibres and numerous short elastic fibres, and is surrounded by skeletal muscle. The single lumen is lined by one to several layers of cuboidal to columnar epithelium in varying stages of degeneration, indicating a holocrine secretory mode. The epithelial cell membranes often interdigitate and tight junctions and desmosomes occasionally are observed between them. The epithelial cells and secretory product contain slight to considerable amounts of lipid; glycoproteins may be present. Crystals exhibiting a dense core and/or layering occur in the epithelial cells and secretory product. Energy-dispersive X-ray analysis demonstrates calcium, copper, iron, lead, potassium, and zinc in the crystals. Mitochondria, vacuoles, and short segments of rough endoplasmic reticulum also occur in the cells.     

Paracloacal glands of Alligator mississippiensis: A histological and histochemical study

The histology of the paracloacal 'musk' glands of adult American alligators ( Alligator mississippiensis ) is described. The gland is a single secretory sac with a single duct and a central lumen partially occluded by a central, cylindrical conglomerate of cells and secretion product. The capsule of the gland consists of an outer layer of smooth muscle and an inner layer of connective tissue containing collagen and elastin fibres. Septa carrying blood vessels radiate from the connective tissue layer of the capsule to the border of the central conglomerate. Parenchymal cells containing lipid droplets enlarge from the periphery to the centre of the gland. Secretions formed by degeneration of cells in the central cylinder are concentrated near the secretory duct. Histochemical tests indicate lipids but not mucopolysaccharides in the glandular exudate.     

Growth dynamics in the American alligator (Alligator mississippiensis)

The growth dynamics of the American alligator ( Alligator mississippiensis ) were studied in the subtropical Florida Everglades using extensive mark-recapture data from over 2000 recaptures of known-aged and unknown-aged animals. A model based on the power curve best describes growth of Everglades alligators. The nonasymptotic character of this curve leads to rejection of the hypothesis that alligator growth is determinate. A model consisting of piece-wise linear equations better described growth in the first year, and suggested a period of arrested growth occurred in the first winter. A comparison of predictions from growth models derived from several populations indicated that Everglades alligators grew more slowly than did those in more temperate areas, leading to the rejection of the hypothesis that growth rates in subtropical Florida would be elevated because of the long growing season. We attribute this result to a combination of increased maintenance costs and a limited resource base in the Everglades.
Analyses considered the extent to which growth model evaluation and use can be affected by data selection. Mathematical constraints posed by negative growth data can be alleviated by including growth records over combined recapture intervals to achieve a positive growth increment. However, periods of no to negative growth may be real, and such deviations are obscured by fitting growth data to monotonically increasing models.     

Glutamine synthetase in liver of the American alligator, Alligator mississippiensis

Glutamine synthetase was shown to be localized in liver mitochondria of the American alligator, Alligator mississippiensis, by immunofluorescent staining of frozen liver sections and by the detection of enzymatic activity and immunoreactive protein in the mitochondrial fraction following subcellular fractionation of liver tissue by differential centrifugation. The primary translation product of alligator liver glutamine synthetase mRNA was shown to have an Mr = 45,000 which is similar if not identical in size to that of the mature subunit. This mRNA was found to be heterogeneous in size with a major form corresponding to 2.8-3.0 kb and a lesser form corresponding to around 2 kb. Both are in excess of the size required to code for the glutamine synthetase subunit. The synthesis and presumably the mitochondrial import of glutamine synthetase in alligator liver are thus very similar to the same processes in avian liver. Despite the excretion of a high percentage of nitrogen as ammonia, the demonstration of a mitochondrial glutamine synthetase indicates the alligator has the typical avian-type uricotelic ammonia-detoxification system in liver. This suggests that the transition to uricotelism occurred in the sauropsid line of evolution and has persisted through both the lepidosaurian (snakes, lizards) and archosaurian (dinosaurs, crocodilians, birds) lines.     

Oogenesis and ovarian histology of the American alligator Alligator mississippiensis

Although folliculogenesis and oogenesis have been observed in numerous reptiles, these phenomena have not been described in detail in a crocodilian. Oogenesis and histological features of the adult ovary of Alligator mississippiensis are described. Using a complex process, the ovary develops telolecithal oocytes that attain a diameter of 38.8 +/- 2.4 mm. The morphology of yolk platelets shows gradual changes throughout the oogenic process. Initially, yolk platelets are seen surrounded by a vesicle. As vitellogenesis advances, the vesicles contain numerous yolk spheres, with slowly growing platelets. The yolk spheres continue to increase in size and number within the vacuoles. Differences in the animal and vegetal poles are seen based on the morphology and size of the yolk platelets. The ovary of A. mississippiensis shows a well-developed system of lacunae and bundles of smooth muscle around the follicles in all stages of development. Several features seen in the ovary of A. mississippiensis are similar to those observed in birds. In particular, the morphology of the yolk platelets, especially during the middle and late vitellogenic stages, and the presence of a ovarian system of lacunae and smooth muscle. These similarities in the reproductive biology of crocodilians and birds contribute to current studies of the evolution of archosaurian reproduction.     

Egg yolk serositis in an American alligator (Alligator mississippiensis)

An adult female American alligator (Alligator mississippiensis) had diffuse, yellow, granular serosal thickening at necropsy. Light microscopic examination of affected stomach, small intestine and spleen revealed a chronic proliferative serositis associated with 3 to 15 micron eosinophilic extracellular globules identified histochemically and morphologically as egg yolk. The intracoelomic egg yolk was considered to be the cause of the serosal reaction.     

Ontogeny of the Middle-Ear Air-Sinus System in Alligator mississippiensis (Archosauria: Crocodylia)

Modern crocodylians, including Alligator mississippiensis, have a greatly elaborated system of pneumatic sinuses invading the cranium. These sinuses invade nearly all the bones of the chondrocranium and several bony elements of the splanchnocranium, but patterns of postnatal paratympanic sinus development are poorly understood and documented. Much of crocodylomorph—indeed archosaurian—evolution is characterized by the evolution of various paratympanic air sinuses, the homologies of which are poorly understood due in large part to the fact that individual sinuses tend to become confluent in adults, obscuring underlying patterns. This study seeks to explore the ontogeny of these sinuses primarily to clarify the anatomical relations of the individual sinuses before they become confluent and thus to provide the foundation for later studies testing hypotheses of homology across extant and extinct Archosauria. Ontogeny was assessed using computed tomography in a sample of 13 specimens covering an almost 19-fold increase in head size. The paratympanic sinus system comprises two major inflations of evaginated pharyngeal epithelium: the pharyngotympanic sinus, which communicates with the pharynx via the lateral (true) Eustachian tubes and forms the cavum tympanicum proprium, and the median pharyngeal sinus, which communicates with the pharynx via the median pharyngeal tube. Each of these primary inflations gives rise to a number of secondary inflations that further invade the bones of the skull. The primary sinuses and secondary diverticula are well developed in perinatal individuals of Alligator, but during ontogeny the number and relative volumes of the secondary diverticula are reduced. In addition to describing the morphological ontogeny of this sinus system, we provide some preliminary exploratory analyses of sinus function and allometry, rejecting the hypothesis that changes in the volume of the paratympanic sinuses are simply an allometric function of braincase volume, but instead support the hypothesis that these changes may be a function of the acoustic properties of the middle ear.     

Organizational Changes to Thyroid Regulation in Alligator mississippiensis: Evidence for Predictive Adaptive Responses

During embryonic development, organisms are sensitive to changes in thyroid hormone signaling which can reset the hypothalamic-pituitary-thyroid axis. It has been hypothesized that this developmental programming is a ‘predictive adaptive response’, a physiological adjustment in accordance with the embryonic environment that will best aid an individual''s survival in a similar postnatal environment. When the embryonic environment is a poor predictor of the external environment, the developmental changes are no longer adaptive and can result in disease states. We predicted that endocrine disrupting chemicals (EDCs) and environmentally-based iodide imbalance could lead to developmental changes to the thyroid axis. To explore whether iodide or EDCs could alter developmental programming, we collected American alligator eggs from an estuarine environment with high iodide availability and elevated thyroid-specific EDCs, a freshwater environment contaminated with elevated agriculturally derived EDCs, and a reference freshwater environment. We then incubated them under identical conditions. We examined plasma thyroxine and triiodothyronine concentrations, thyroid gland histology, plasma inorganic iodide, and somatic growth at one week (before external nutrition) and ten months after hatching (on identical diets). Neonates from the estuarine environment were thyrotoxic, expressing follicular cell hyperplasia (p = 0.01) and elevated plasma triiodothyronine concentrations (p = 0.0006) closely tied to plasma iodide concentrations (p = 0.003). Neonates from the freshwater contaminated site were hypothyroid, expressing thyroid follicular cell hyperplasia (p = 0.01) and depressed plasma thyroxine concentrations (p = 0.008). Following a ten month growth period under identical conditions, thyroid histology (hyperplasia p = 0.04; colloid depletion p = 0.01) and somatic growth (body mass p<0.0001; length p = 0.02) remained altered among the contaminated sites. This work supports the hypothesis that embryonic EDC exposure or iodide imbalance could induce adult metabolic disease states, thereby stressing the need to consider the multiple environmental variables present during development.     

扬子鳄与密河鳄基因组DNA的复性动力学和组织结构的研究

通过DNA复性动力学的分析,测定了扬子鳄和密河鳄基因组的组织结构,两者的复性曲线非常相象,高度重复DNA含量很少,而中度重复DNA序列各占基因组的30％左右。中度重复序列部分能再分成三个组分,虽然每个组分的序列复杂性和拷贝数有差别,但每部分的总复杂性是相似的。我们已测得扬子鳄基因组的单拷贝序列为3.68×10’bp,基因组为5.65×10’bp;密河鳄基因组的单拷贝序列为3.67×10’bp,基因组为5.24×10’bp。根据基因组的组织结构的分析,在分子水平上表明两种鳄鱼是亲缘关系十分相近的种。