Serum catecholamine and hormonal titers in the hibernating snake Naja haje haje, with reference to the annual climatic cycle

Unexpected lack of specialisation in the flow properties of spitting cobra venom

Venom spitting is a defence mechanism based on airborne venom delivery used by a number of different African and Asian elapid snake species ('spitting cobras'; Naja spp. and Hemachatus spp.). Adaptations underpinning venom spitting have been studied extensively at both behavioural and morphological level in cobras, but the role of the physical properties of venom itself in its effective projection remains largely unstudied. We hereby provide the first comparative study of the physical properties of venom in spitting and non-spitting cobras. We measured the viscosity, protein concentration and pH of the venom of 13 cobra species of the genus Naja from Africa and Asia, alongside the spitting elapid Hemachatus haemachatus and the non-spitting viper Bitis arietans By using published microCT scans, we calculated the pressure required to eject venom through the fangs of a spitting and a non-spitting cobra. Despite the differences in the modes of venom delivery, we found no significant differences between spitters and non-spitters in the rheological and physical properties of the studied venoms. Furthermore, all analysed venoms showed a Newtonian flow behaviour, in contrast to previous reports. Although our results imply that the evolution of venom spitting did not significantly affect venom viscosity, our models of fang pressure suggests that the pressure requirements to eject venom are lower in spitting cobras than in non-spitting cobras.

Hormonal correlates of the annual cycle of activity and body temperature in the South-American tegu lizard (Salvator merianae)

Life history transitions and hormones are known to interact and influence many aspects of animal physiology and behavior. The South-American tegu lizard (Salvator merianae) exhibits a profound seasonal shift in metabolism and body temperature, characterized by high daily activity during warmer months, including reproductive endothermy in spring, and metabolic suppression during hibernation in winter. This makes S. merianae an interesting subject for studies of interrelationships between endocrinology and seasonal changes in physiology/behavior. We investigated how plasma concentrations of hormones involved in regulation of energy metabolism (thyroid hormones T₄ and T₃; corticosterone) and reproduction (testosterone in males and estrogen/progesterone in females) correlate with activity and body temperature (Tb) across the annual cycle of captive held S. merianae in semi-natural conditions. In our initial model, thyroid hormones and corticosterone showed a positive relationship with activity and Tb with independent of sex: T₃ positively correlated with activity and Tb, while T₄ and corticosterone correlated positively with changes in Tb only. This suggests that thyroid hormones and glucocorticoids may be involved in metabolic transitions of annual cycle events. When accounting for sex-steroid hormones, our sex separated models showed a positive relationship between testosterone and Tb in males and progesterone and activity in females. Coupling seasonal endocrine measures with activity and Tb may expand our understanding of the relationship between animal's physiology and its environment. Manipulative experiments are required in order to unveil the directionality of influences existing among abiotic factors and the hormonal signaling of annual cyclicity in physiology/behavior.

Seasonal changes in plasma concentrations of the thyroid, glucocorticoid and reproductive hormones in the tegu lizard Salvator merianae

The tegu lizard Salvator merianae is a large, widely distributed teiid lizard endemic to South America that exhibits annual cycles of high activity during the spring and summer, and hibernation during winter. This pattern of activity and hibernation is accompanied by profound seasonal changes in physiology and behavior, including endothermy during the austral spring. The unusual combination of seasonal endothermy, hibernation and oviparity, in a non-avian, non-mammalian species, makes S. merianae an interesting subject for study of comparative aspects of endocrine regulation of seasonal changes in physiology. In the present study, we first validated commercially available immunoassay kits for quantification of hormone concentrations of the reproductive (testosterone, estradiol and progesterone), adrenal (corticosterone), and thyroid [thyroxine (T₄) and triiodothyronine (T₃)] axes in plasma of an outdoor, captive adult male and female S. merianae in southeastern Brazil. All assays exhibited parallelism and accuracy with S. merianae plasma. We next assessed patterns of concentration of these hormones across the annual cycle of S. merianae. Testosterone in males and estradiol in females peaked in spring coincident with the peak in reproductive behavior. Progesterone in females was significantly elevated in October coincident with putative ovulation when gravid females build nests. Thyroid hormones, known for regulating energy metabolism, varied seasonally with some sex-dependent differences. T₄ gradually increased from an annual nadir during pre-hibernation and hibernation to high concentrations during spring in both sexes. In contrast, T₃ did not vary seasonally in males, but females showed a two-fold increase in T₃ during the spring reproductive season. T₃ may be involved in energy investment during the seasonal production of large clutches of eggs. Corticosterone was significantly elevated during the active season in both sexes, suggesting its involvement in mobilization of energy stores and modulation of behavior (territoriality) and physiology. Ours is the first investigation of concurrent changes in reproductive, thyroid and adrenal hormone concentrations in this endemic and physiologically unique South American lizard. Our findings set the stage for future investigations to determine the extent to which these hormones influence activity and thermoregulation in S. merianae.

Urinary iodine and stable isotope analysis to examine habitat influences on thyroid hormones among coastal dwelling American alligators

The American alligator, generally a freshwater species, is known to forage in marine environments despite the lack of a salt secreting gland found in other crocodylids. Estuarine and marine foraging could lead to increased dietary uptake of iodine, a nutrient necessary for the production of thyroid hormones. To explore the influence of dietary iodine on thyroid hormone health of coastal dwelling alligators, we described the seasonal plasma thyroxine and triiodothyronine concentrations measured by radioimmunoassay and urinary iodine (UI) concentrations measured by inductively coupled plasma mass spectrometry. We also analyzed long-term dietary patterns through stable isotope analysis of scute tissue. Snout-to-vent length (SVL) was a significant factor among UI and stable isotope analyses. Large adult males greater than 135cm SVL had the highest UI concentrations but did not display seasonality of thyroid hormones. Alligators under 135 SVL exhibited seasonality in thyroid hormones and a positive relationship between UI and triiodothyronine concentrations. Isotopic signatures provided supporting evidence that large males predominantly feed on marine/estuarine prey whereas females showed reliance on freshwater/terrestrial prey supplemented by marine/estuarine prey. UI measurement provided immediate information that correlated to thyroid hormone concentrations whereas stable isotope analysis described long-term dietary patterns. Both techniques demonstrate that adult alligators in coastal environments are utilizing estuarine/marine habitats, which could alter thyroid hormone physiology.

Vesicular, ulcerative, and necrotic dermatitis of reptiles

Vesicular, ulcerative, and necrotic dermatologic conditions are common in captive reptiles. Although these conditions have distinct differences histologically, they are commonly sequelae to each other. This article examines the anatomy and physiology of reptile skin; discusses reported causes of vesicular, ulcerative, and necrotic dermatologic conditions; and reviews various management options.

Seasonal variation in plasma thyroid hormone concentrations in coastal versus inland populations of juvenile American alligators (Alligator mississippiensis): influence of plasma iodide concentrations

Thyroid hormones, essential for normal growth and health, are associated with changes in temperature, photoperiod, and reproduction. Iodide, a necessary element for thyroid hormone production, varies in diet, and is more abundant in estuarine environments, which could alter thyroid hormone variation. However, associations between thyroid hormone concentrations in animals from marine versus freshwater environments, which could become more pertinent with rising sea levels associated with global climate change, are not well studied. To determine the importance of dietary iodide in seasonal variation of plasma thyroid hormone concentrations, we analyzed seasonal variation of plasma thyroxine (T(4)) and triiodothyronine (T(3)) concentrations in juvenile alligators from an estuarine habitat (Merritt Island National Wildlife Refuge; MI) and a freshwater habitat (Lake Woodruff National Wildlife Refuge; LW) and compared these results to plasma inorganic iodide (PII) concentrations. Alligators from MI did not display seasonal variation in plasma T(4), but exhibited a seasonal pattern in plasma T(3) concentrations similar to alligators from LW. Plasma thyroid hormone concentrations were consistently higher at MI than at LW. PII concentrations were correlated with plasma T(4) and T(3) concentrations in juvenile alligators from LW but not MI. The data on plasma T(4) and T(3) concentrations suggest altered iodide metabolism in estuarine alligators. Differences in thyroid hormone concentrations between the populations could be due to differences in dietary iodide, which need to be further evaluated.