Clearance rates of sessile rotifers: in vitro determinations

We measured laboratory clearance rates of 10 rotifer and one unidentified bryozoan species from 3 different lakes using ³²P labeled algae (Chlamydomonas) or yeast (Rhodotorula). Clearance rates for all rotifers fed yeast ranged from < 2.0 to > 260 µl · animal^–1 · h^–1 depending on species. The in vitro clearance rates of two sessile rotifers (Ptygura crystallina and P. pilula) were not significantly different from previously measured in situ rates (Wallace and Starkweather 1983). Clearance rates for 5 rotifers fed algae ranged from < 5.0 to > 90.0 µl · animal^–1 · h^–1. Ptygura beauchampi, P. crystallina, P. pilula, Floscularia conifera, and F. melicerta ingested both cell types but their clearance rates varied substantially among species and between cell types. There was a substantial time-dependent loss of 32P from formalin-fixed animals (Sinantherina socialis) awaiting processing. This loss stabilized at approximately 20 hours and was estimated to be about 40% of the initial ingested label. Clearance rates for the bryozoan fed yeast or algae were highly variable, ranging from < 1.0 to > 3 000 µl · animal^–1 · h^–1.     

Ultrastructural studies on plastids of generative and vegetative cells inLiliaceae 3. Plastid distribution during the pollen development inGasteria verrucosa (Mill.) Duval

Summary This paper describes the development of pollen grains ofGasteria verrucosa from the late microspore to the mature two-cellular pollen grain. Ultrastructural changes and the distribution of plastids as a result of the first pollen mitosis have been investigated using light and electron microscopy. The microspores as well as the generative and the vegetative cell contain mitochondria and other cytoplasmic organelles during all of the observed developmental stages. In contrast, the generative cell and the vegetative cell show a different plastid content. Plastids are randomly distributed within the microspores before pollen mitosis. During the prophase of the first pollen mitosis the plastids become clustered at the proximal pole of the microspore. The dividing nucleus of the microspore is located at the distal pole of the microspore. Therefore, the plastids are not equally distributed into both the generative and the vegetative cell. The possible reasons for the polarization of plastids within the microspore are briefly discussed. The lack of plastids in the generative cell causes a maternal inheritance of plastids inGasteria verrucosa.     

A test of a model for planktivorous filter feeding by bream Abramis brama

Synopsis The planktivorous feeding of bream, Abramis brama on Daphnia hyalina and Bosmina coregoni was analyzed in a stepwise regression analysis with the average size (and standard deviation) of consumed organisms as dependent variable and the size of the fish, the average size (and standard deviation) of the organisms and their density in the environment as independent variables. Three basic predictions on filter feeding were formulated and tested. It was predicted that the (average) prey size should increase with fish size, but that the standard deviation should decline. Secondly the prey size should be strongly correlated with the prey size available and thirdly the prey density should have little effect on the size selection. These hypotheses could not be rejected for bream>10 cm feeding on B. coregoni and for bream>20 cm feeding on D. hyalina. The hypotheses were not valid for smaller bream as these acted as particulate or combined filter- and particulate feeders.     

Pollenfertility and seed formation in theOrnithogalum umbellatum/angustifolium complex (Liliaceae/Scilloideae)

The pollen fertility and seed formation of six species of theOrnithogalum umbellatum/angustifolium complex and of seven related species were studied. Four types of pollen grains could be recognized. The pollen fertility varied greatly in this complex and is not related to the ploidy level. The seed formation ofO. umbellatum showed an adaptation to a subcontinental-Mediterranean climate, that ofO. angustifolium to an Atlantic climate. In both cases raindrops seem to be important for pollination, in view of the absence of insect pollinators. After open pollination 113 seedlings were obtained in four species. Their chromosome numbers were determined. Nearly all the cultivated seedlings were aneuploid, which points to a positive selection of euploids in nature, because aneuploid individuals are rare in the wild.Biosystematic Studies on theOrnithogalum umbellatum/angustifolium Complex III.—Previous parts of this series are Part I: Taxonomy. Proceeding Kon. Ned. Acad. Wet. series C,85 (4), 563–574 (1982) andvan Raamsdonk (1984).     

Compensation by locusts for changes in dietary nutrients: behavioural mechanisms

ABSTRACT. The detailed behavioural mechanisms underlying an instance of compensation for changes in dietary nutrients are described for the first time in an insect. Nymphs of Locusta migratoria L. were given one of four artificial diets on the third day of the fifth instar, and their feeding patterns recorded in detail for 12 h. The diets represented combinations of two protein and two digestible carbohydrate levels (28% and 14% dry weight) presented in an otherwise complete nutrient mix. At the nutrient levels used, locusts regulated their intake of food with respect to protein but not digestible carbohydrate in the diet. They ate more of the lower protein diets by eating the same sized meals more frequently than insects fed on the higher protein diets. Compensation was not complete over the 12 h observation period: insects on the lower-protein diets ingested and absorbed 72% as much nitrogen as those insects fed on the higher-protein diets. Possible physiological mechanisms underlying the behavioural mechanisms are discussed.     

Food and feeding habits of Labeo niloticus (Pisces,Cyprinidae) in Jebel Aulia Reservoir,Sudan

Basic knowledge on the feeding ecology of one of the common and commercially important fish species in Jebel Aulia Reservoir is provided.The structure of the feeding apparatus indicates that Labeo niloticus is a bottom feeder, depending on soft and decayed vegetation, organic debris and whatever small organisms found within. However, juveniles and fry are prone to explore all layers and depths of the river selectively for plankton. There is little evidence of seasonal selection of food. Changes in diet quality are governed by the availability of type of food. Variability of feeding activity is connected with climate and breeding season.     

14C-Metabolism in cultured cotyledon explants of radiata pine

Excised cotyledons of radiata pine ( Pinus radiata D. Don), cultured under shootforming (plus cytokinin) and elongating (minus cytokinin) conditions, were incubated in ¹⁴C-glucose, ¹⁴C-acetate or ¹⁴C-bicarbonate at different stages of growth and differentiation. ¹⁴CO₂ was produced when the cotyledons were fed ¹⁴C-glucose and ¹⁴C-acetate (no measurement was made for ¹⁴C-bicarbonate feeding). Label from these precursors was incorporated into ethanol-soluble and -insoluble fractions. The largest percentage of radioactivity was associated with the ethanol-soluble portion, which was further fractionated into lipids, amino acids, organic acids and sugars. The amount of label and the pattern of labelling associated with each of the above classes of metabolites varied with time in culture and morphogenetic behaviour of the cotyledons. In general, there was a tendency towards a high rate of incorporation of label in elongating cotyledons during the period of rapid elongation. On the other hand, a high rate of incorporation of label in shoot-forming cotyledons coincided with the period of meristematic tissue formation. The data obtained support the hypothesis that organized development in vitro involves a shift in metabolism, which precedes and is coincident with the initiation of the process.     

Pollen morphology of Solanurn L. section Solanum

J. M. EDMONDS, 1984. Pollen morphology of Solanum L. section Solnnum . The pollen morphology of both dried and fresh, fixed material was examined using SEM. The work confirmed thc spheroidal to sub-prolate shape, the tricolporate nature and the granular surface sculpturing, typical of Solanurn pollen, but failed to demonstrate the occurrence of exine patterns which could bc of practical taxonomic use is differentiating the species belonging to the section Solanurn . Quantification of the exine sculpturing, by means of granule density counts, indicated a possible relationship between this feature and the morpho-genetic diversity of certain species.     

Feeding ecology of the earliest vertebrates

Based on protochordates and extant fish, the earliest Palaeozoic vertebrates were microphagous suspension-feeding animals that pumped food-carrying water very slowly and thus required highly concentrated suspensions. Such conditions exist in benthic (not open water) aquatic environments. Feeding modes which on the basis of extant fish are closely related to benthic microphagous suspension feeding include deposit feeding, epilithic algal scraping, and macrophagous suspension feeding; early jawless vertebrates are predicted to have included all these feeding types. The gnathostome condition is predicted to have followed an initial switch from feeding on suspensions to taking tiny individual food particles (microphagous suspension-feeding → microphagous particulate-feeding → macrophagous particulate-feeding).