CRETACEOUS PLANKTONIC FORAMINIFERA FROM BORNHOLM AND THEIR ZOOGEOGRAPHIC SIGNIFICANCE

Late Cretaceous formations exposed along the south coast of Bornholm Island, Denmark, contain well preserved assemblages of planktonic foraminifera, which are described and illustrated. Two taxa, Whiteinella baltica and Hedbergella bornholmensis , are described as new. The oldest assemblage, Middle to early Upper Cenomanian in age, is essentially monospecific and indicative of a restricted pelagic environment. The overlying Lower Senonian faunules are diverse, contain large populations which are associated with other pelagic microfossils, and provide a more typical example of Boreal planktonic foraminiferal associations. Taxonomically the assemblages are largely composed of species of Hedbergella, Whiteinella, Archaeoglobigerina, Globigerinelloides , and Heterohelix and double-keeled species of Globotruncana , particularly G. marginata. These species are widely distributed in space and time. Thus Bornholm assemblages have a cosmopolitan aspect, which can be identified in microfaunas from the Western Interior of North America and Alaska. Because of the lower diversity, lack of restricted stratigraphic markers, Lower Senonian correlations between Bornholm, and probably Boreal pelagic microfaunas generally, coeval Tethyan assemblages are less precise than within the Tethys.     

Equilibration of Adenylates by Maize Leaf Adenylate Kinase: Effects of Magnesium on Apparent and True Equilibria

In this study, the effect of magnesium on equilibration of adenylatesby purified maize leaf adenylate kinase (AK) was investigated.The equilibration was expressed in terms of either apparentequilibrium constant, defined as K_app=(ATP_total)(AMP_total)/(ADP_total)²,or true equilibrium constant, defined as K_true=(Mg-ATP)(AMP_free)/(Mg-ADP)(ADP_free).At a fixed concentration of free magnesium (1?8–1?9 mM),the K_app, and K_true were constant at 0?76?0?10 and 6?02?0?75,respectively. On the other hand, at the free magnesium rangeof 0?00l4 to 8?3 mM, the K_app varied from 0?30 to 1?27, whileremained constant at 5?93?0?31. The data indicate that, contraryto previous speculations, leaf AK does not maintain an equilibriumof total adenylates. Rather, the enzyme governs an equilibriumof Mg-ADP, free ADP, Mg-ATP, and free AMP, which are the truesubstrates/products of the AK reaction. Some implications ofthis finding for studies on energy metabolism in plant tissuesare discussed. Key words: Adenylate kinase, adenylate energy charge, adenylates, C₄-photosynthesis, magnesium     

Forest landscape pattern in the KwaZulu–Natal midlands,South Africa: 50 years of change or stasis?

Abstract Understanding patterns and processes of habitat change is essential for managing and conserving forest fragments in anthropogenically altered landscapes. Digitized aerial photographs from 1944 and 1996 were examined for changes to the indigenous forest landscape in the Karkloof‐Balgowan archipelago in KwaZulu–Natal, South Africa. Attributes relating to proximate land‐use, patch shape, isolation and position in the landscape were used to determine putative causes of forest change. The total change in forest area was ?5.7% (forest covered 6739 ha in 1996). This is contrasted with previous reports for the period 1880–1940 that estimated change in total forest area of up to ?80%. Attrition was the predominant process of forest transformation between 1944 and 1996. Despite little overall change in forest area, 786 mostly small (<0.5 ha) forest patches were lost from the landscape, leaving 1277 forest patches in 1996. An increase in patch isolation, but no change in patch cohesion accompanied the changes in forest area. Ignoring patches that were eliminated, 514 patches decreased in area. This was partly a function of patch size, but the conversion of natural grassland to commercial plantation forestry in the matrix also influenced forest decline. Their small size and irregular shape caused forest patches in the region to be vulnerable to edge effects. Core area declined in a negative exponential way with increasing edge width and the total area of edge habitat exceeded that of core habitat at an edge width of only 50 m. Nevertheless, total core area decreased by only 2% (65 ha) between 1944 and 1996 because most of the eliminated patches were small and contained no core area. The large Karkloof forest (1649 ha) is a conservation priority for forest interior species, but the ecological role and biodiversity value of small forest patches should not be overlooked.     

The Irradiation of Dividing Cells: Changes in Sensitivity to X-Rays during Mitosis

Roots of Vicia faba were given combined X-ray and colchicinetreatments. Breaks were not visible immediately after irradiation,even at metaphase. Breaks and reunions were, therefore, scoredlater in 2x nuclei, and in the 4x nuclei derived from 2x nucleiafter colchicine treatment. It was shown that metaphase is themost sensitive stage of mitosis Breaks per chromosome are less frequent in 4x nuclei than in2x nuclei after irradiation of resting stage. This apparentphysiological difference between the two types of nuclei mayaffect either the frequency of breakage or of restitution. Afterthe irradiation of prophase, metaphase, or telophase cells,however, breaks per chromosome are more frequent in the 4x nucleithan they are in 2x nuclei in the same sample owing to the factthat the 2x, unlike the 4x nuclei, are not accurately timed.They must include cells irradiated during the less sensitiveresting stage. Chromosome reunion occurred, probably at telophase. Chromatidreunion and sister reunion did not occur frequently. Chromatidbreaks, like chromatid reunions, were infrequent except afterirradiation of resting stage cells. The evidence indicates thatthe chromosome, at metaphase just as at resting stage, reactsto X-rays as a single functional unit.     

MARSUPIAL ANATOMY OF THE DEMIBRANCH OF MARGARITIFERA MARGARITIFERA (LIN.) IN NORTHEASTERN NORTH AMERICA (PELECYPODA: UNIONACEA)

On morphological, biological and behavioral characters the freshwatermussel family Margaritiferidae generally is accepted as themost primitive of the Unionacea. Microscopic examination ofthe marsupial demibranch further supports this assumption, inthat the interlamellar junctions lack elastic properties necessaryfor lateral hyperextension of the gravid demibranch. A temporarymodification of marsupial anatomy in the form of a fibrous elastinaccessory material is produced during the final phase of glochidialincubation. Its appearance coincides with the enlargement ofepithelial cells that line the marsupium and interlamellar junctions.The material, which is situated between the glochidial massand the inner lamellar surfaces, may provide increased aerationand support for the resting glochidia. (Received 18 February 1978;     

Parental role division predicts avian preen wax cycles

Previous studies have shown that preen wax composition in some sandpipers shifts from the usual monoesters to diesters during the breeding season, possibly to reduce the ability of mammalian predators to find nests using olfactory cues. To investigate further the relationship between incubation and wax secretion, we examined seven sandpiper species with different incubation patterns (species in which both sexes incubate, in which only males incubate and in which only females incubate). During the breeding period, diester preen wax was secreted almost exclusively by the incubating sex in species with uniparental incubation, and by both sexes in species with biparental incubation. These findings suggest that diester preen waxes have a function that is directly related to incubation. Unexpectedly, in female-incubating Curlew Sandpiper Calidris ferruginea and Buff-breasted Sandpiper Tryngites subruficollis , some males also secreted diester preen waxes during the breeding period. This suggests that some males may in fact incubate, that these waxes may be a remnant from their evolutionary past when both sexes incubated, or that males need to be olfactorally cryptic because they are involved in the making of nest scrapes. The seasonal pattern of preen wax composition was also studied in captive male, female and female-mimicking male ('faeder') Ruff Philomachus pugnax . Captive female Ruff changed preen wax composition from monoesters to diesters in the spring despite the fact that no incubation took place. This suggests that circannual rhythms rather than actual incubation behaviour may trigger the shift to diester waxes. All captive male Ruff, including the faeders, continued to secrete monoesters, supporting the hypothesis that only the incubating sex secretes diesters.