Embryonic and larval respiration in the arboreal foam nests of the African frog Chiromantis xerampelina.

In Zimbabwe, female Chiromantis xerampelina construct spherical foam nests that are suspended above temporary water. The nests average 624 ml in volume and contain 854 eggs. The 1.7 mm ova have exceptionally thin jelly capsules and are dispersed in the foamy core of the nest, which is surrounded by a layer of eggless foam. At 25 degrees C, each embryo requires 3.5 days to reach hatching at developmental stage 22, during which it consumes 30 microliters of oxygen. After hatching, each larva remains in the nest for 2 more days and consumes a further 123 microliters of oxygen. The fresh foam contains 77% air, which is sufficient to supply all of the oxygen requirements of the embryos until well after they hatch. Therefore, the size of the egg mass is not limited by oxygen availability as it is in many other anurans. Oxygen also diffuses into the nest from the atmosphere, but the rate is severely restricted by the wet foam, despite the presence of bubbles. Drying of the outer layer of foam greatly increases its oxygen conductance, but the larvae remain in the inner core of wet foam, where they compete for oxygen at the periphery. With further drying of the nest, the wet foam diminishes in volume and concentrates the larvae at a time when their oxygen demands are approaching the maximum. Oxygen pressures within the wet foam drop below 10 kPa and oxygen uptake by the larvae becomes progressively limited, possibly stimulating their emergence from the nest. The delay between hatching and escape from the nest permits the larvae to grow and mature to a stage at which all of the clutch can emerge simultaneously.

Endocrines and osmoregulatory mechanisms in the Nile crocodile, Crocodylus niloticus.

The changes in body fluid economy and endocrine status associated with exposure of the Nile crocodile, Crocodylus niloticus, to hypertonic media have been related to the responses to altered renin-angiotensin system (RAS) activity observed in fresh water (FW) animals. Animals held in hypertonic media for 7 days showed a 18.2% body weight loss and raised plasma and urinary sodium, potassium, chloride, and osmotic concentrations. Within 6 hr of return to FW rapid imbibition had largely restored body weight and produced significant plasma dilution. Although plasma sodium, chloride, and osmotic concentrations remained higher than in FW controls, plasma levels of corticosterone, aldosterone, and arginine vasotocin were not significantly altered. Angiotensin I (AI) administration in FW crocodiles stimulated drinking and raised plasma aldosterone levels by comparison with animals given the converting enzyme inhibitor, Captopril, together with AI. The compensatory drinking behaviour exhibited by the Nile crocodile may thus involve the RAS. The RAS also appears to influence interrenal steroidogenesis and thus may afford an integrative role in crocodile fluid management as it does in homeotherms.

Nile crocodiles, Crocodylus niloticus, and estuarine crocodiles, Crocodylus porosus, show similar osmoregulatory responses on exposure to seawater.

1. Nile crocodiles, reared in fresh water and exposed acutely to seawater, suffer marked dehydration and hypernatraemia. Cloacal urine osmolarity and potassium concentration increased markedly but urine sodium remains low. 2. Hypernatraemia is increased when secretion from the lingual salt glands is prevented. 3. C. niloticus appears not to drink seawater. 4. Similarities in osmoregulatory response between estuarine and Nile crocodiles suggest that the lingual salt glands of C. niloticus are functional in salt water, playing an important role in sodium balance. 5. Significant differences in the function of the renal/cloacal complex of Alligator and Crocodylus emphasize further the differences between these two groups of crocodilian and provide support for the postulated marine ancestry of many or all of the Crocodylidae.

Biologically active gastrin/CCK-related peptides in the stomach of a reptile, Crocodylus niloticus; identified and characterized by immunochemical methods.

We have used immunochemical, chromatographic, and bioassay techniques to characterize peptides related to gastrin and CCK, from the stomach of the reptile Crocodylus niloticus. By immunocytochemistry gastrin/CCK-like peptides were localized in specific mucosal cells of the pylorus and in the duodenum. Boiling water extracts of pyloric antrum cross reacted with four antisera specific for the C-terminal region of gastrin or CCK, but estimates of concentration varied between antisera. Antisera specific for the N-terminus of heptadecapeptide gastrin (G17), intact G17, or the amphibian CCK-like peptide caerulein did not cross react with the crocodile extracts. Gel filtration of the extracts on Sephadex G50 resolved one major peak eluting significantly before G17 or CCK8, suggesting larger molecular size, whereas ion exchange on DE52 cellulose resolved two major immunoreactive peaks, both eluting before G17, indicating that they are less acidic. The more acidic of the two peptides stimulated gastric acid secretion in the rat, but had no CCK-like actions on the rat pancreas. Thus crocodile antrum contains gastrin-like peptides, which are however clearly distinguishable from any of the known mammalian forms of gastrin and CCK.

Heat loss from feet of herring gulls at rest and during flight.

The role of the feet of herring gulls (Larus argentatus) in heat dissipation was estimated during rest and wind-tunnel flight. We determined the blood flow to the feet and the arteriovenous temperature difference and thus estimated heat loss from the feet. Determinations of oxygen consumption and respiratory water loss at rest gave a heat production of about 8 W; 37-56% of this heat was lost from the feet (air temp = 10-35 degrees C). During flight heat production was estimated to be about 57 W and heat loss from the feet was 46 W, about 80% of the heat production in flight. Thus the webbed feet are an important avenue of heat loss in the herring gull.