Elasmosaur (Reptilia: Sauropterygia) neck flexibility: implications for feeding strategies.

Elasmosaurs were extremely long-necked, aquatic reptiles that used four flippers for locomotion. Their distinctive long neck distinguishes them from all other Mesozoic forms, yet the potential uses and constraints of this structure are poorly understood, particularly with regard to feeding. Several associated series of elasmosaurian cervical vertebrae were used to measure ranges of potential flexion. Two-dimensional models, based on a complete specimen of the Late Cretaceous elasmosaur Aphrosaurus furlongi, were created to measure mobility in both vertical and horizontal planes. Accuracy of the models was assessed through comparative analyses with currently extant vertebrate analogues (e.g. snake, turtle, seal). Results suggest that the elasmosaurian neck was capable of a 75-177 degrees ventral, 87-155 degrees dorsal, and 94-176 degrees lateral range of movement depending upon the thickness of cartilage reconstructed between each vertebra. Neck postures such as a 'swan-like' S-shape are shown to be implausible because they require >360 degrees vertical flexion. However, maintenance of a straight neck while swimming, together with considerable lateral and/or ventral movement during prey capture and feeding are feasible.     

Ultrastructural localization of amiloride-sensitive sodium channels and Na+,K(+)-ATPase in the rat's olfactory epithelial surface

Several studies have indicated that olfactory responses are impeded by amiloride. Therefore, it was of interest to see whether, and if so which, olfactory epithelial cellular compartments have amiloride- sensitive structures. Using ultrastructural methods that involved rapid freezing, freeze-substitution and low temperature embedding of olfactory epithelia, this study shows that, in the rat, this tissue is immunoreactive to antibodies against amiloride sensitive Na(+)- channels. However, microvilli of olfactory supporting cells, as opposed to receptor cilia, contained most of the immunoreactive sites. Apices from which the microvilli sprout and receptor cell dendritic knobs had much less if any of the amiloride-antibody binding sites. Using a direct ligand-binding cytochemical method, this study also confirms earlier ones that showed that olfactory receptor cell cilia have Na+, K(+)-ATPase. It is proposed that supporting cell microvilli and the receptor cilia themselves have mechanisms, different but likely complementary, that participate in regulating the salt concentration around the receptor cell cilia. In this way, both structures help to provide the ambient mucous environment for receptor cells to function properly. This regulation of the salt concentration of an ambient fluid environment is a function that the olfactory epithelium shares with cells of transporting epithelia, such as those of kidney.      

The Renal Cortical Na+/HCO3 − Cotransporter VI: The Effect of Chemical Modification in Cotransporter Activity

The Na⁺/HCO₃ ⁻ cotransporter is the main system that mediates bicarbonate removal out of the proximal tubule cell into the blood. We have previously partially purified this protein and showed that chemical modification of the α-amino groups by fluorescein isothiocyanate (FITC) inhibited the activity of the Na⁺/HCO₃ ⁻ cotransporter. The inhibition was prevented by the presence of Na and bicarbonate suggesting that this compound binds at or near the substrate transport sites of the cotransporter. We examined the effect of agents that modify the sulfhydryl group (dithiothreitol), carboxyl groups (n-n′dicyclohexyl carbodiimide) and tyrosine residues (p-nitrobenzene sulfonyl fluoride, n-acetyl imidazole and tetranitromethane) on the activity of the cotransporter to gain insight into the chemical residues which may be important for transport function. The sulfhydryl residues modifier, carboxyl group modifier, and tyrosine modifier significantly inhibited bicarbonate dependent ²²Na uptake in basolateral membranes by 50–70% without altering the ²²Na uptake in the presence of gluconate indicating that these agents directly affected the cotransporter without affecting diffusive sodium uptake. The effect of the tyrosine modifier n-acetylimidazole was not prevented by the presence of Na and bicarbonate suggesting that the tyrosine residues are not at the substrate binding sites. To determine the presence and role of glycosylation on the Na⁺/HCO₃ ⁻ cotransporter protein, we examined the effects of different glycosidases (endoglycosidase F and H, N-glycosidase F, O-glycanase) on the cotransporter activity. All glycosidases caused a significant 50–80% inhibition of cotransporter activity. These data demonstrate that N-glycosylation as well as O-glycosylation are important for the function of the Na⁺/HCO₃ ⁻ cotransporter protein. Taken together, these results suggest that chemical modifiers of tyrosine, carboxyl and sulfhydryl groups as well as glycosylation are important for expression of full functional activity of the cotransporter. Received: 8 October 1996/Revised: 23 January 1997     

THE FOOD AND FEEDING APPARATUS OF THE BLUE DUCK HYMENOLAIMUS

This paper describes a preliminary study of the feeding behaviour of the territorial Blue Duck. The bird is unusual in possessing lateral bill flaps and, in a number of head and skull characters, differs from a typical dabbling duck. Herbst's corpuscles are absent from the outer 60% of the width of the flaps and this is thought to indicate that any tactile function is subsidiary. It is tentatively suggested that an additional function is protective, and that the flaps cushion the jaw edges during vigorous food searching beneath stones on rocky stream bottoms. Food taken in summer was analysed from remains in droppings and from gut contents and was found to consist of aquatic insects, principally case-living and free-living caddis larvae, and algae. Some short-term variation in the diet was noted. It is suggested, also tentatively, that the decline in Blue Duck numbers since the 19th century has been associated with the introduction of trout which are potentially direct food competitors. Further ecological research on this unique species is required.     

A pulse-position-modulated multichannel radio telemetry system for the study of the avian nest microclimate

A multichannel biotelemetry system using pulse position modulation has been developed to monitor continuously the environment in birds' nests. Probes to measure temperature at six points, relative humidity, light and egg attitude, together with a transmitter and power supply are contained in a fibreglass shell, having the shape, size and weight of the egg of the species being studied. The sensing egg is placed in the nest at the completion of a clutch and not removed until the young have hatched. A low-power transponder is used to relay the signals up to 2 miles to a data-logging system in the laboratoy.