Sex Determination and Sex Ratios in Crocodylus palustris

Incubation temperature determines sex in the mugger crocodile,Crocodylus palustris. Exclusively females are produced at constanttemperatures of 28.0°C through 31°C. At 32.5°C,only males are produced. Both sexes are produced in varyingproportions at 31.5, 32.0, and 33.0°C. Embryo survival isnot affected within this range, but developmental rate and totalincubation time are strongly temperature dependent. In naturalnests laid in breeding enclosures, cool incubation temperaturesproduced only females whereas males were produced only in warmnests. Clutch sex ratios were female or male biased. Yearlysex ratios (=percent male) varied from 0.05 to 0.58; overallsex ratio during six nesting seasons was 0.24 (1 male: 3 females).Sex ratio and incubation time vary with nest location and temperaturein a manner consistent with the constant temperature results.Incubation time decreases with increasing incubation temperature,and is an accurate predictor of sex ratio in the field and laboratory. To date, temperature-dependent sex determination (TSD) has beenreported in five species of Crocodylus and in three speciesof Alligatorinae; but the TSD patterns in these groups differ.The TSD pattern of C. palustris is similar to that of C. porosus.Nesting in C. palustris is synchronized with the seasonal availabilityof thermal regimes suitable for incubation. Resultant sex ratiosare a consequence of when and where eggs are laid. Early nestsare located in warm, sunny sites; in contrast, late season nestsare located in the shade. An egg transplant experiment demonstratedthat sex ratios could be altered by simple manipulations ofnest temperatures in the field. The adaptive significance ofTSD in crocodilians may relate to the influence of incubationtemperature on various hatchling attributes, particularly growth.     

Activity and Properties of Macrophage Migration Inhibitory Factor produced by Mixed Lymphocyte Cultures

THE macrophage migration test is an in vitro demonstration of delayed hypersensitivity. Supernatant fluids of sensitive lymphocytes cultured for 24 h in the presence of specific antigen contain migration inhibitory factor (MIF) that arrests the migration of macrophages of unsensitized animals in vitro¹,². In vivo, it induces delayed skin reactions³. The use of the macrophage migration test, based on differences of transplantation antigens in donor and recipient, to show histocompatibility has been suggested⁴. The test was also recommended as an indicator of immunological reactivity after organ transplantation, to demonstrate impending rejection⁵. It can demonstrate homograft sensitivity, for migration of peritoneal exudate cells (containing lymphocytes and macrophages) of CBA mice previously sensitized by grafts from A/Jax donors was inhibited when they were mixed with peritoneal exudate cells of the donor strain. However, histocompatibility was not demonstrated, for mixtures of peritoneal exudate cells of ungrafted CBA mice and A/Jax mice migrated regularly during the 24 h test⁶.     

Induction and Reversal of Contact Inhibition of Growth by <Emphasis Type="Italic">p</Emphasis>H Modification

MANY normal mammalian cells in culture are sensitive to a growth-inhibitory effect of cellular interaction, evidenced by an almost complete arrest of macromolecular synthesis and cellular division at relatively low population densities (contact inhibition of growth)¹. It has, however, been shown that the environmental pH is an important element in this phenomenon². In the bicarbonate-buffered media ordinarily used for animal cell cultures, an initial alkalinization to pH 7.8–8.0 as a result of CO₂ loss is followed by the metabolic acidification of the medium to pH 6.8–7.0, at a rate determined by the population density and the metabolic activity of the specific cell. If, by the use of appropriate non-volatile buffers^3,4, cells are kept at or near the pH optimal for the specific strain (H. E., unpublished work), the early contact inhibition of growth does not develop and the cells achieve population densities as much as two to four times greater than those ordinarily observed².     

Net primary production and light use efficiency in a mixed coniferous forest in Sweden

Simple light use efficiency (ɛ) models of net primary production (NPP) have recently been given great attention (NPP = ɛ × absorbed photosynthetically active radiation). The underlying relationships have, however, not been much studied on a time step less than a month. In this study daily NPP was estimated as the sum of net ecosystem exchange (NEE) and heterotrophic respiration (R_h) of a mixed pine and spruce forest in Sweden. NEE was measured by eddy correlation technique and R_h was estimated from measurements of forest floor respiration (R_f) and the root share of R_f. The total yearly NPP was on average 810 g C m⁻² year⁻¹ for 3 years and yearly ɛ was between 0.58 and 0.71 g C MJ⁻¹, which is high in comparison with other studies. There was a seasonal trend in ɛ with a relatively constant level of approximately 0.90 g C MJ⁻¹ from April to September Daily NPP did not increase for daily intercepted radiation above 6 MJ m⁻² d⁻¹, indicating that between-years variation in NPP is not directly dependent on total Q_i. The light was most efficiently used at an average daytime temperature of around 15 °C. At daytime vapour pressure deficit above 1400 Pa ɛ was reduced by approximately 50%.     

Siphuncular structure in the orders Tarphycerida and Barrandeocerida (Cephalopoda: Nautiloidea)

Abstract: The siphuncular structure is described in two Silurian taxa, Boionautilus tyrannus and Cumingsoceras complanatus, currently placed in the Tarpycerida. Tarphycerids have the Nautilus type of connecting ring that is composed of an outer, thick, spherulitic‐prismatic layer and an inner glycoprotein layer, the latter was destroyed by diagenesis. However, both Silurian specimens have the connecting ring of the calcified‐perforate type, previously known to occur in orthocerids, actinocerids, plectronocerids and now also in barrandeocerids. In this type, the inner layer of the connecting ring is calcified and perforated by pore canals. Boionautilus and Cumingsoceras are therefore classified with barrandeocerids and not with tarphycerids.     

Composition of Pneumocystis carinii Neutral Lipids and Identification of Coenzyme Q10 as the Major Ubiquinone Homolog

The lipids of purified preparations of Pneumocystis carinii carinii freshly isolated from infected rats were analyzed and compared with those of whole lungs from normal and methylprednisolone-immunosuppressed uninfected rats. In this study, the neutral lipid fraction was examined in detail; the relative concentrations of individual classes making up this fraction were quantified. Of particular interest was the nature of the organism's ubiquinone (coenzyme Q, CoQ) fraction because atovaquone, a hydroxynaphtho-quinone (566C80) analog of ubiquinone, is efficacious in the treatment of P. carinii pneumonia. The ubiquinone concentration in both P. carinii and lung tissues was relatively low compared to that present in rat heart and liver tissues. Two homologs were identified in the organism: CoQ₁₀ was the predominant homolog with lesser amounts of CoQ₉ present. In contrast, the lungs of normal and immunosuppressed uninfected rats had CoQ₉ and lesser amounts of CoQ₈, but no detectable CoQ₁₀. Furthermore, radiolabeled mevalonic acid was incorporated in vitro into the ubiquinone fraction of P. carinii indicating that the organism has the de novo branch of the isoprenoid biosynthetic pathway leading to polyprenyl formation. Hence, it was concluded that CoQ₁₀ (if not both CoQ1₁₀ and CoQ₉) in P. carinii as not scavenged from the host but was synthesized by the organism. Although lung tissues contained substantial free fatty acids, the organism was enriched in these lipids. The high concentration of free fatty acids and relatively low level of triglycerides in P. carinii suggest that fatty acids may represent major carbon sources for ATP production by the organism.