Stage-Dependent Effects of Chloroquine on Plasmodium falciparum In Vitro1

The erythrocytic developmental cycle of Plasmodium falciparum can be conveniently divided into the ring, trophozoite, and schizont stages based on morphology and metabolism. Using highly synchronous cultures of P. falciparum, considerable variation was demonstrated among these stages in sensitivity to chloroquine. The effects of timed, sequential exposure to several clinically relevant concentrations of chloroquine were monitored by three techniques: morphological analysis, changes in the rate of glucose consumption, and changes in the incorporation of ³H-hypoxanthine into parasite nucleic acids. All three techniques gave essentially identical results. The trophozoite and schizont stages were considerably more sensitive to the drug than ring-stage parasites. Chloroquine sensitivity decreased as nuclear division neared completion. The increase in chloroquine sensitivity was coincident with a marked rise in the rate of glucose consumption and nucleic acid synthesis. The rate of nucleic acid synthesis decreased as schizogony progressed while glucose consumption continued at high rates during this process. The degree of chloroquine sensitivity was not highly correlated with either metabolic activity.     

Natural convection from leaves at realistic Grashof numbers

Abstract. The boundary layer resistance of model leaves was measured in still air, at a range of leaf-to-air temperature differences. The results were compared to those calculated from standard formulae for natural convection. The agreement between observed and calculated was only satisfactory when Grashof numbers exceeded about 105. At the lower Grashof numbers, which often prevail in nature, the observed rates of heat transfer considerably exceeded those calculated.     

Comparative Studies of Reproductive Behavior in Mantis Shrimps and Fiddler Crabs

Comparative ethological studies of closely related species canplace into clear perspective the functions of behavioral traitsas species diverge and adapt to different environments. In thispaper we contrast the reproductive behavior of species withintwo crustacean groups: the mantis shrimps (stomatopods) andthe fiddler crabs (genus Uca). For the stomatopods, we identifyprobable selective relationships between features of species'ecology and their mating systems. Population density, the kindand availability of shelters in which these shrimps live, theintensity of predation and spawning cycles all play importantroles in molding reproductive behavior in this group. Associationsbetween the ecology and mating systems of fiddler crabs havebeen discussed recently elsewhere. Here we focus on a comparativeanalysis of sexual communication in these crabs. A study ofcompetitive courtship signaling and mate choice in the fiddlercrab Uca beebei has shown that certain male courtship signalsare highly attractive probably because they exploit female sensory-responsesystems that have been molded by selection for escape from predators.Interspecific comparison of male courtship displays and theresponses of females to these displays suggest that sensoryexploitation may play an important role in the evolution ofsexual signals in the genus. Comparative studies have advancedour understanding of how natural and sexual selection affectthe reproductive behavior of both stomatopods and fiddler crabs.     

Nitrogen mineralization and nitrification in rainforests of contrasting nutrient status and physiognomic structure near Lake Eacham,northeast Queensland

Nitrogen mineralization and nitrification were measured using in situ incubations for 12 periods of 1 month in a structurally complex rainforest with basaltic soil, and an adjacent structurally simple rainforest with less fertile soil formed on metamorphic rock. The study was undertaken near Lake Eacham on the Atherton Tableland in northeast Queensland. Cumulative nitrogen mineralization for 1 year did not differ between forests. It amounted to 265 ± 13 μg N g^-1 oven dry soil at the upper position (0–7.5 cm) and 122 ± 11 μg N g^-1 oven dry soil at the lower position (7.5–15 cm; mean ± s.e. for pooled data). Rates were highest during the wet season but were not strongly correlated with moisture content or temperature. Relative nitrification (cumulative nitrate-nitrogen production expressed as a percentage of cumulative nitrogen mineralization) at the upper position was significantly higher in the complex than the simple forest (100% c.f. 88%). At the lower position it amounted to 100% for cumulative data in both forests. Nitrate was the dominant form of inorganic nitrogen in the complex forest but in the simple forest nitrate and ammonium were of similar importance. The association between forest physiognomic structure and nutrient status at Lake Eacham represents a more general pattern in rainforests of northeast Queensland and further study is needed to ascertain whether results from this study apply more generally.     

Dimorphism in a Tethyan early Jurassic Juraphyllites

A lappeted microconch specimen of the phylloceratid ammonoid Juraphyllites from the Tethyan Jurassic of Anatolia (Turkey) indicates that sexual dimorphism in this group was established as early as in the early Lower Pliensbachian (Lower Jurassic) and that dimorphism in this genus of the Phylloceratina follows the same pattern as that proven [or many groups of the Ammonitina. This is the earliest record of well-developed lateral lappets in the Mesozoic Ammonoidea     

Three New Species of Lagenophryid Peritrichs (Ciliophora) Ectocommensal on Freshwater Decapod Crustaceans from Madagascar1

One species of Lagenophrys and two species of Operculigera are described for the first time. Lagenophrys machaerigera n. sp. was discovered on the freshwater crab Gecarcinautes goudoti and varies between two extreme forms in the structure of its lorica aperture. Operculigera carcini n. sp. was also found on G. goudoti and exhibits several characteristics that set it apart from other members of its genus. Some of these characteristics also suggest a phylogenetic link between O. carcini and the genus Lagenophrys. Operculigera madagascarensis n. sp. was discovered on the parastacid crayfish Astacoides granulimanus. The occurrence of O. madagascarensis on a Madagascan parastacid and other species of Operculigera on Chilean parastacids suggests that parastacids are the oldest hosts of the genus Operculigera. Continental drift is the most likely mechanism by which species of Operculigera and parastacids could have been dispersed to distant parts of the southern hemisphere. The absence of Operculigera on Australian parastacids may be due to its replacement by the genus Setonophrys on those hosts.     

Decapod Larvae: Dispersal, Mortality, and Ecology. A Working Hypothesis

TWO topics on decapod larval biology are discussed: retentionand recruitment of decapod larvae to the parental populationand the ecological role of decapod larvae in the water column. Most decapods have retained a planktonic larval phase whichis generally interpreted as a mechanism for increased dispersal.Evidence of restricted gene flow and biological/physical interactionresearch have suggested that larvae can be retained and recruitedto the parental population via mesoscale processes. To fullyunderstand recruitment processes improved estimates of mortalityrates for planktonic larval stages will be required. Recentevidence suggests that mortality rates are not constant overthe complete larval developmental period but decrease with time. During some seasons meroplankton including decapod l arvae canconstitute more than 50% of the plankton biomass. The quantityof energy transferred into the water column can be significant.Their role in planktonic ecology may be significant and additionalresearch is required.     

Uptake of DOM by Nemertean Worms: Association of Worms with Arthrodial Membranes

SYNOPSIS. Carcinonemertes errans is a nemertean worm, the juvenilesof which are found as epibionts on the Dungeness crab, Cancermagister, in close association with the arthrodial membranesof the crabs. The juvenile nemerteans appear to have no meansof taking in particulate food but survive for many months onthe surface of the host. We show that the juvenile C. erransare capable of removing amino acids from dilute solution insea water, that the water near the arthrodial membranes wherethe worms are found contains high concentrations of primaryamines, and that there is a low resistance pathway for low molecularweight amino acids across the arthrodial membrane examined invitro.