The Role of Exchange in Productive Specialization

Nomadic pastoralists are specialists in complex systems of land use. Their own productive strategies are dependent in large part upon the conversion rates of their products to imported items from other sectors of a larger economy. Changes in these conversion rates are likely to arise for a number of reasons; pastoralists respond to such changes in various ways, depending upon their past histories and current conditions. The case of the Yörük, specialized pastoralists of southeastern Turkey, is used to illustrate this process of changing productive strategies. Generalizations are sought concerning the ways in which large systems of land use become more or less specialized through time, in terms of the consequences of shifting exchange conditions for the productive strategies of component households. [economic anthropology, pastoralism, complex society, interpopulation exchange]     

Hydrolytic extracellular enzyme activity in heterotrophic biofilms from two contrasting streams

SUMMARY. 1. Extracellular hydrolytic enzyme activities and cell densities were monitored during undisrupted biofilm formation on pristine surfaces in two contrasting river sites in North Wales: an oligotrophic mountain stream (Nant Waen) and a mildly eutrophic river (River Clywedog).
2. Bacterial densities generally increased at both sites over a 33-day monitoring period. Densities in the eutrophic site were approximately 14 times greater than in the mountain stream.
3. Using fluorescent substrate analogues, biofilms from Nant Waen produced low, variable xylosidase and β-glucosidase activities. Biofilms from the more eutrophic River Clywedog produced higher xylosidase and β-glucosidase activities and detectable endopeptidase, though these activities also fluctuated during the colonization period.
4. Unlike the other activities measured, esterase activities in the River Clywedog were correlated with cell densities ( P <0.05). When extracellular esterase activities per cell were calculated, the oligotrophic biofilm was found to contain about twice as much extracellular esterase activity as the more eutrophic River Clywedog biofilm.     

Fine Structure of Human Malaria In Vitro*†

SYNOPSIS. The erythrocytic cycle of the human malaria parasite, Plasmodium falciparum, was examined by electron microscopy. Three strains of parasites maintained in continuous culture in human erythrocytes were compared with in vivo infections in Aotus monkeys. The ultrastructure of P. falciparum is not altered by continuous cultivation in vitro. mitochondria contain DNA-like filaments and some cristae at all stages of the erythrocytic life cycle. The Golgi apparatus is prominent at the schizont stage and may be involved in the formation of rhoptries. In culture, knob-like protrusions first appear on the surface of trophozoite-infected erythrocytes. The time of appearance of knobs on cells in vitro correlates with the life cycle stage of parasites which are sequestered from the peripheral circulation in vivo. Knob material of older parasites coalesces and forms extensions from the erythrocyte surface. Some of this material is sloughed from the host cell surface. The parasitophorous vacuole membrane breaks down in erythrocytes containing mature merozoites both in vitro and in vivo. Merozoite structure is similar to that of P. knowlesi. The immature gametocytes in culture have no knobs.     

Pollen Ontogeny in Catananche caerulea L. (Compositae: Lactuceae) II. Free Microspore Stage to the Formation of the Male Germ Unit

The development of Catananche caerulea pollen grains from theearly free microspore stage to the formation of the male germunit has been studied using the scanning electron microscope.The differentiation of the elaborate ectexine from primexineand the accompanying cytoplasmic changes in the microsporesare described. Changes in the tapetum, reflecting first theformation of sporopollenin precursors and then of pollenkitt,are also described. The origin of taxonomically important featuresis discussed. Catananche caerulea, Compositae: Lactuceae, microspore mitosis, male germ unit, ontogeny, primexine differentiation, scanning electron microscopy     

Functional Morphology of Mammalian Mastication

SYNOPSIS. While chewing is not unique to mammals, it is oneof their most distinctive characteristics. Historically, studiesof food processing in mammals were intended to provide evolutionaryinsights, but more progress has been made in understanding mechanisticaspects. Mastication is considered under five headings. (1)Interaction of teeth with food.Knowledge of comparative dentalanatomy and function is advanced in comparison to understandingof foods and how they are broken down. (2) Chewing force andits resistance by the skull. The traditional assumption thatocclusal force is maximized is not always justified, and experimentalresults suggest that skull loading is far more dynamic and variablethan had been envisioned from theoretical analyses. (3) Howthe jaw moves. The most important masticatory movement is thatof the power stroke, and in most but not all species this isinfluenced more by the inclined planes of the teeth and jawjoints than by the musculature. (4) The role of muscles in producingboth force and movement. The most fundamental distinction amongjaw muscles is whether they have a rostral or caudal directionof pull, as this determines their role in transverse jaw movements.Reliance on anatomical names tends to obscure functional similaritiesand differences among species. (5) Intraoral structures. Becausethey are difficult to study, the actions of the tongue and pharynxare still debated. Even the fundamental question of whethermammals can breathe and swallow at the same time has not beendefinitively answered.     

Fluorescently-labeled Oligonucleotide Probes Can Be Used To Identify Protistan Food Vacuole Contents

ABSTRACT. In situ hybridization using fluorescent oligonucleotide probes complementary to unique regions of 16S rRNA molecules provides a way of identifying the food vacuole contents of bactivorous protists. Laboratory experiments with Tetrahymena showed rRNAs in food vacuoles are degraded slowly enough to permit their use as hybridization targets for such probes. A probe specific for a hypervariable region of the small subunit rRNA of an unnamed proteobacterium abundant in a local lake was then synthesized. It was used to probe the food vacuoles of the ciliates present in fixed water samples collected from the same lake. The vacuoles of several filter-feeding ciliates bound the probe, indicating that such probes can be used to identify the food vacuole contents of ciliates collected from natural samples.     

A Century of Sea Urchin Development

SYNOPSIS. In the last quarter of the nineteenth century severalinvestigators including Richard and Oskar Hertwig, Theodor Boveri,Hans Driesch, Curt Herbst, T. H. Morgan and others turned theirattention to sea urchin eggs and early embryos. This favorablecombination of outstanding investigators and the sea urchinembryo as an experimental organism contributed to a fundamentalunderstanding of the cell, fertilization and heredity. The advantagesof the sea urchin continued to be recognized as experimentalembryologists used these embryos to develop the concepts ofgradients, regulative development and inductive interactions.Then, as developmental biology arose from chemical embryology,the sea urchin embryo once again emerged as an ideal experimentalanimal, pivotal in the understanding of the molecular and developmentalbiology of eukaryotic organisms.