Juvenile Caiman Research Articles

The external genitalia in juvenile Caiman latirostris differ in hormone sex determinate-female from temperature sex determinate-female

The broad-snouted caiman (Caiman latirostris) is a crocodilian species that inhabits South American wetlands. As in all other crocodilians, the egg incubation temperature during a critical thermo-sensitive window (TSW) determines the sex of the hatchlings, a phenomenon known as temperature-dependent sex determination (TSD). In C. latirostris, we have shown that administration of 17-β-estradiol (E2) during the TSW overrides the effect of the male-producing temperature, producing phenotypic females (E2SD-females). Moreover, the administration of E2 during TSW has been proposed as an alternative way to improve the recovery of endangered reptile species, by skewing the population sex ratio to one that favors females. However, the ovaries of E2SD-female caimans differ from those of TSD-females. In crocodilians, the external genitalia (i.e. clitero-penis structure or phallus) are sexually dimorphic and hormone-sensitive. Despite some morphological descriptions aimed to facilitate sexing, we found no available data on the C. latirostris phallus histoarchitecture or hormone dependence. Thus, the aims of this study were: (1) to establish the temporal growth pattern of the phallus in male and female caimans; (2) to evaluate histo-morphological features and the expression of estrogen receptor alpha (ERα) and androgen receptor (AR) in the phallus of male and female pre-pubertal juvenile caimans; and (3) to determine whether the phallus of TSD-females differs from the phallus of E2SD-females. Our results demonstrated sexually dimorphic differences in the size and growth dynamics of the caiman external genitalia, similarities in the shape and spatial distribution of general histo-morphological compartments, and sexually dimorphic differences in innervation, smooth muscle fiber distribution, collagen organization, and ERα and AR expressions. The external genitalia of E2SD-females differed from that of TSD-females in many histological features and in the expression of ERα and AR, resembling patterns described in males. Our results alert on the effects of estrogen agonist exposure during TSW and suggest that caution must be taken regarding the use of E2SD as a procedure for wildlife population management.

The respiratory mechanics of the yacare caiman (Caiman yacare).

The structure and function of crocodilian lungs are unique compared with those of other reptiles. We examined the extent to which this and the semi-aquatic lifestyle of crocodilians affect their respiratory mechanics. We measured changes in intratracheal pressure in adult and juvenile caiman (Caiman yacare) during static and dynamic lung volume changes. The respiratory mechanics of juvenile caiman were additionally measured while the animals were floating in water and submerged at 30, 60 and 90deg to the water's surface. The static compliance of the juvenile pulmonary system (2.89±0.22 ml cmH2O-1100 g-1) was greater than that of adults (1.2±0.41 ml cmH2O-1100 g-1), suggesting that the system stiffens as the body wall becomes more muscular and keratinized in adults. For both age groups, the lungs were much more compliant than the body wall, offering little resistance to air flow (15.35 and 4.25 ml cmH2O-1100 g-1 for lungs, versus 3.39 and 1.67 ml cmH2O-1100 g-1 for body wall, in juveniles and adults, respectively). Whole-system dynamic mechanics decreased with increasing ventilation frequency (fR), but was unaffected by changes in tidal volume (VT). The vast majority of the work of breathing was required to overcome elastic forces; however, work to overcome resistive forces increased proportionally with fR Work of breathing was higher in juvenile caiman submerged in water at 90deg because of an increase in work to overcome both elastic and flow resistive forces. The lowest power of breathing was found to occur at high fR and low VT for any given minute ventilation (V̇E) in caiman of all ages.

Corticosterone levels and immunological indices in stressed juvenile broad‐snouted caimans

AbstractThe effect of stress in wild vertebrates has been little investigated, especially in crocodilians. In the wild, crocodilians face numerous stressors such as climatic factors, toxicant exposure, and infection. Exposure to stressors may affect the physiological processes of crocodilians, with consequences on its fitness and survival. We experimentally investigated the effect of a 4‐week exposure to environmental challenges (food restriction, water restriction and high temperature) on growth, immunological investment and corticosterone levels of juvenile Caiman latirostris. White blood cells counts, natural antibody (NAb) levels and complement system activity were evaluated to characterize the influence of those treatments on the immune system. We found deprivation of food resulted in reduction in growth and body condition, whereas high temperature had a beneficial effect on the variables measured. Individuals exposed to heat treatment (37 ± 1°C) grew more, and obtained better body condition, higher NAb levels, and significantly lower corticosterone levels relative to caimans in all other groups. Food restricted caimans also illustrated higher NAb levels. Our findings suggest that C. latirostris juveniles are able to tolerate environmental stressors and they are even favored by high temperatures.

Crocodilian Forebrain: Evolution and Development.

Organization and development of the forebrain in crocodilians are reviewed. In juvenile Caiman crocodilus, the following features were examined: identification and classification of dorsal thalamic nuclei and their respective connections with the telencephalon, presence of local circuit neurons in the dorsal thalamic nuclei, telencephalic projections to the dorsal thalamus, and organization of the thalamic reticular nucleus. These results document many similarities between crocodilians and other reptiles and birds. While crocodilians, as well as other sauropsids, demonstrate several features of neural circuitry in common with mammals, certain striking differences in organization of the forebrain are present. These differences are the result of evolution. To explore a basis for these differences, embryos of Alligator misissippiensis were examined to address the following. First, very early development of the brain in Alligator is similar to that of other amniotes. Second, the developmental program for individual vesicles of the brain differs between the secondary prosencephalon, diencephalon, midbrain, and hindbrain in Alligator. This is likely to be the case for other amniotes. Third, initial development of the diencephalon in Alligator is similar to that in other amniotes. In Alligator, alar and basal parts likely follow a different developmental scheme.

Food habits of the Broad‐snouted Caiman (Caiman latirostris: Crocodylia, Alligatoridae) in northwestern Uruguay

The food habits of the Broad‐snouted Caiman (Caiman latirostris) were studied in northwestern Uruguay. The most common prey were insects, the shrimp Pseudopalaemon bouvieri, the snail Pomacea canaliculata, fish and birds. Spiders, crabs, amphibians, snakes, turtles and mammals were consumed less frequently. Arthropods were the most frequent prey for juvenile caiman. Fish and snails were consumed by all size classes. The proportion of stomach contents with invertebrates decreased with increasing caiman size, and that with vertebrates was greater in the diet of larger caiman. Diet composition and ontogenetic shift are similar to that of other crocodilians considered as opportunistic generalist predators. Se estudiaron los hábitos alimenticios del Yacaré (Caiman latirostris) en el noroeste de Uruguay. Las presas más comunes fueron insectos, el camarón Pseudopalaemon bouvieri, el caracol Pomacea canaliculata, peces y aves. Arañas, cangrejos, anfibios, serpientes, tortugas y mamíferos fueron consumidos menos frecuentemente. Los artrópodos fueron las presas más frecuentes de juveniles. Peces y aves fueron consumidos por todos los tamaños. La proporción de contenidos estomacales con invertebrados disminuyó al aumentar el tamaño de los caimanes, y la de vertebrados fue mayor en los individuos de mayor tamaño. La composición y cambio ontogenético en la dieta resultan similares a los de crocodilianos considerados predadores generalistas oportunistas.

Developmental exposure to endocrine disruptor chemicals alters follicular dynamics and steroid levels in Caiman latirostris

Human and wildlife are exposed at critical periods of development to endocrine disruptor chemicals (EDC) that may be responsible for reproductive disorders. To test the hypothesis that in ovum exposure to EDC at a critical period for gonadal organogenesis alters post-hatching folliculogenesis and steroidogenesis in Caiman latirostris, we studied the impact of in ovum exposure to 17β-estradiol (E2), bisphenol A (BPA), endosulfan (END) and atrazine (ATZ) on gonadal differentiation, follicular dynamics and circulating levels of steroid hormones in neonatal and juvenile caiman. Since C. latirostris is a species with temperature dependent sex determination, eggs were incubated at male (33°C) or female (30°C) producing temperatures and the effect of EDC was evaluated. Neonatal ovaries exhibited germ cells mainly located in clusters evidencing proliferative activity and type I to III follicles. Juvenile ovaries exhibited germ cells and advanced stages of pre-vitellogenic follicles. Prenatal exposure to the highest doses of E2 (1.4ppm) or BPA (140ppm) overrode male temperature effect on sex determination. Neonatal females produced by sex reversion lacked type III follicles, while females prenatally exposed to the lowest doses of E2 (0.014ppm) and BPA (1.4ppm) or ATZ (0.2ppm) showed an increase in type III follicles. Juvenile caiman prenatally exposed to E2 or BPA showed an augmented incidence of multioocyte follicles. Neonatal female caiman exposed in ovum to E2 or BPA had higher estrogen serum levels whereas exposure to E2, BPA, ATZ and END decreased T levels. Present data demonstrates that exposure to EDC during gonadal organogenesis alters follicular dynamics and steroid levels later in life. These effects might have an impact on caiman fertility.

Biomechanics of the rostrum in crocodilians: A comparative analysis using finite‐element modeling

This article reports the use of simple beam and finite-element models to investigate the relationship between rostral shape and biomechanical performance in living crocodilians under a range of loading conditions. Load cases corresponded to simple biting, lateral head shaking, and twist feeding behaviors. The six specimens were chosen to reflect, as far as possible, the full range of rostral shape in living crocodilians: a juvenile Caiman crocodilus, subadult Alligator mississippiensis and Crocodylus johnstoni, and adult Caiman crocodilus, Melanosuchus niger, and Paleosuchus palpebrosus. The simple beam models were generated using morphometric landmarks from each specimen. Three of the finite-element models, the A. mississippiensis, juvenile Caiman crocodilus, and the Crocodylus johnstoni, were based on CT scan data from respective specimens, but these data were not available for the other models and so these--the adult Caiman crocodilus, M. niger, and P. palpebrosus--were generated by morphing the juvenile Caiman crocodilus mesh with reference to three-dimensional linear distance measured from specimens. Comparison of the mechanical performance of the six finite-element models essentially matched results of the simple beam models: relatively tall skulls performed best under vertical loading and tall and wide skulls performed best under torsional loading. The widely held assumption that the platyrostral (dorsoventrally flattened) crocodilian skull is optimized for torsional loading was not supported by either simple beam theory models or finite-element modeling. Rather than being purely optimized against loads encountered while subduing and processing food, the shape of the crocodilian rostrum may be significantly affected by the hydrodynamic constraints of catching agile aquatic prey. This observation has important implications for our understanding of biomechanics in crocodilians and other aquatic reptiles.

The Behavior of Juvenile Alligator mississippiensis and Caiman crocodilus Exposed to Low Temperature

The Behavior of Juvenile Alligator mississippiensis and Caiman crocodilus Exposed to Low Temperature

Morphology and function of the parathyroid gland of the caiman, Caiman crocodilus

The juvenile caiman, Caiman crocodilus, possesses two to six parathyroid glands which are embedded in the thymus, one to three on either side of the body. The number is subject to individual variation. In specimens having three parathyroids on one side of the body, the smallest may be designated as an accessory parathyroid. The parathyroid gland is composed of parenchymal cells arranged in cords among which rich connective tissue and blood capillaries are present. The general features of the parathyroid histology of the present specimens resemble those reported in other groups of reptiles. Normal serum calcium, sodium, and phosphorus concentrations are 15.2 ± 0.30, 332.7 ± 2.42, and 3.4 ± 0.32 mg/100 ml, respectively. Surgical parathyroidectomy caused a significant decrease of serum calcium concentration (about 50–60% of the normal) 5 and 10 days after the operation together with simultaneous occurrence of tetanic convulsions. However, no changes were observed in serum sodium concentrations. Serum phosphorus concentration increased 5 days after parathyroidectomy. Administration of mammalian parathyroid extract (0.2 USP units/g body wt) partially corrected the hypocalcemia which was caused by parathyroidectomy. The present results suggest that the role of the crocodilian parathyroid gland in serum calcium and phosphorus homeostasis is very similar to that of the Squamata but somewhat different from that of the Chelonia.

INFLUENCE OF ESTROGENS AND ANDROGENS ON THE SKELETAL SYSTEM

ArticlesINFLUENCE OF ESTROGENS AND ANDROGENS ON THE SKELETAL SYSTEMW. U. Gardner, and Carroll A. PfeifferW. U. Gardner, and Carroll A. PfeifferPublished Online:01 Apr 1943https://doi.org/10.1152/physrev.1943.23.2.139MoreSectionsPDF (4 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByThe development of medullary bone: A model for osteogenesisComparative Biochemistry and Physiology Part A: Physiology, Vol. 82, No. 1The effect of estrogens on erythroid stem cells in polycythemic miceMolecular and Cellular Endocrinology, Vol. 24, No. 1Sexual dimorphism of canine teeth of small dogsArchives of Oral Biology, Vol. 24, No. 8ADVANCES IN OSTEOPOROSISThe Lancet, Vol. 308, No. 7984The effects of estradiol valerate on the serum and bone of hatchling and juvenile caiman crocodiles (Caiman sclerops)Comparative Biochemistry and Physiology, Vol. 25, No. 2The citric acid content of blood plasma and tissues of the domestic fowlComparative Biochemistry and Physiology, Vol. 11, No. 2Metabolic and radioactive tracer studies in carcinoma of the prostateThe American Journal of Medicine, Vol. 29, No. 2Metabolic observations in adult hypophosphatasiaThe American Journal of Medicine, Vol. 29, No. 2OsteoporosisThe American Journal of Medicine, Vol. 22, No. 5Heritable disorders of connective tissueJournal of Chronic Diseases, Vol. 3, No. 2OSTEOPOROSISThe Lancet, Vol. 265, No. 6871The Effect of Estrogen on the Gingiva and Alveolar Bone of Molars in Rats and Mice9 November 2016 | Journal of Dental Research, Vol. 33, No. 1 More from this issue > Volume 23Issue 2April 1943Pages 139-165 https://doi.org/10.1152/physrev.1943.23.2.139History Published online 1 April 1943 Published in print 1 April 1943 Metrics