Role of Silicon in Diatom Metabolism

The in vivo uptake of ³¹Si-silicic acid and ⁶⁸Ge-germanic acid by cell organelles of Nitzschia alba Lewin and Lewin and Cylindrotheca fusiformis Reimann and Lewin was demonstrated. The organelles were isolated by fractionation of pre-labeled cells by differential centrifugation in 0.4 M sucrose medium. Electron micrographs showed that the isolated organelles were intact, with the exception of the N. alba mitochondria which appeared swollen and the C. fusiformis chloroplasts which had ruptured outer membranes and lacked stroma material. The amount of ³¹Si or ⁶⁸Ge per mg protein of the subcellular fractions decreased in the following general order for both organisms: cell wall, mitochondria, chloroplasts, vesicles, and microsomes. A portion of the ³¹Si or ⁶⁸Ge in the organelle fractions could be extracted into a distilled water wash. The uptake of silicon by the organelles suggests that silicon may be involved in some processes of the compartmentalized systems of the cell.     

Structure and Function of Mitochondria in Crithidia fasciculata*

SYNOPSIS. In correlating mitochondrial structure with composition and function of the electron-transport system in Crithidia fasciculata, failure to find cytochrome oxidase in isolated mitochondria coincided with the presence of longitudinally-oriented lamellar cristae in the mitochondria in intact cells. Cytochromes b and c were detected spectrophotometrically. Respiration of intact cells and mitochondria, measured polarographically, was sensitive to 10⁻⁴ M antimycin A and 5 × 10⁻⁴ M KCN. The difficulty in detecting cytochrome oxidase and the biogenesis of mitochondria are briefly discussed.     

Accumulation of Uric Acid in the Land Crab, Cardisoma guanhumi

Variable amounts of white particulate matter occur in the hemocoelof the land crab, Cardisoma guanhumi. This material, mainlyuric acid, accounts for 0.2–15.9% of the total dry weightof a series of crabs. The material appears to increase duringintermolt. Concentrations of uric acid in the blood varied from0.2 to 13.2 mg/100 ml. Urine and feces contained little or nouric acid. Estimates of NH₃-N (3.9 mg/100 ml) in the blood of C. guanhumiare higher, and those of non-protein N (10.2 mg/100 ml) arelower, than corresponding values reported for other decapods.The crab's rate of nitrogen release (0.4 mg/10 g/day) into wateris similar to that reported for other terrestrial crustaceans.About one-third of this is released as NH₃. The urine of C.guanhumi is frequently nearly free of nitrogen, and its stomachfluid contains about five to seven times as much as does itsblood. Implications of these findings in the crab's metabolismand excretion are discussed.     

Visual Displays in Brachyuran Crabs: Field and Laboratory Studies

Study of the visual displays of more than 30 species of crabsallows some generalizations on the Brachyrhyncha. The displaysfall into two groups, the Lateral Merus and the Chela Forward.Each group contains three major subtypes of display, which originatedas discrete signals of intensity. Several special ritualizationsof the Lateral Merus have evolved in certain genera. The LateralMerus seems to be the primitive type of display in the Brachyuraand still exists in most crabs. It is speculated that the ChelaForward arose from a specialized courtship display but has beenadopted for general agonistic use in some genera.     

Adaptations of the Ribbed Mussel, Modiolus demissus (Dillvvyn), to the Intertidal Habitat

SYNOPSIS. This is a review of the behavioral, biochemical-physiological,and morphological adaptations of Modiolus demissus (Dillwyn)to the high intertidal habitat. The ribbed mussel, Modiolus,has fully exploited the behavioral adaptations within the limitsimposed by the bivalve body plan. Air-gaping is undoubtedlya significant behavioral adaptation which permits aerial respirationand penetration of the high intertidal zone. Modiolus fullyutilizes physiological-biochemical adaptations also. The musselis both eurythermal and euryhaline: the thermal range is atleast 56 °C and the salinity range is at least 70%, bothimpressive ranges for an organism which conforms to these environmentalparameters. The two primary adaptations made by Modiolus arean extensive tolerance to dehydration and a very high enzymethermostability. These two adaptations are resjxmsible for Modiolus'tolerance toward desiccation, variation in salinity, thermalstress, and possibly anaerobic conditions. There is no obviousmorphological adaptation. Thus, the physiological adaptations,coupled with air-gaping, are responsible for the vertical penetrationof Modiolus into the intertidal zone and its horizontal migrationover an extensive geographic range.     

THE SINGER AND THE SONG: ON THE RECEIVING END OF BIRD SONG

Variation in singing behaviour between males can involve fixed differences such as the song type composition of repertoires, as well as more flexible effects such as matched counter-singing (Krebs & Kroodsma, 1980; Section III. 4), differences in bout length (the number of songs in a period of song) and changes in strophe length. Short-term strophe length changes seem to be related to the willingness and ability of males to respond strongly to playback. Whether this is because strophe length indicates motivation or the degree of exhaustion of the neuromuscular song-production system, or both, is currently unclear.