Influences of sea level changes and volcanic eruptions on Holocene vegetation in Tonga

Here, we investigate Mid- to Late-Holocene vegetation changes in low-lying coastal areas in Tonga and how changing sea levels and recurrent volcanic eruptions have influenced vegetation dynamics on four islands of the Tongan archipelago (South Pacific). To investigate past vegetation and environmental change at Ngofe Marsh (‘Uta Vava’u), we examined palynomorphs (pollen and spores), charcoal (fire), and sediment characteristics (volcanic activity) from a 6.7-m-long sediment core. Radiocarbon dating indicated the sediments were deposited over the last 7700 years. We integrated the Ngofe Marsh data with similar previously published data from Avai’o’vuna Swamp on Pangaimotu Island, Lotofoa Swamp on Foa Island, and Finemui Swamp on Ha’afeva Island. Plant taxa were categorized as littoral, mangrove, rainforest, successional/ disturbance, and wetland groups, and linear models were used to examine relationships between vegetation, relative sea level change, and volcanic eruptions (tephra). We found that relative sea level change has impacted vegetation on three of the four islands investigated. Volcanic eruptions were not identified as a driver of vegetation change. Rainforest decline does not appear to be driven by sea level changes or volcanic eruptions. From all sites analyzed, vegetation at Finemui Swamp was most sensitive to changes in relative sea level. While vegetation on low-lying Pacific islands is sensitive to changing sea levels, island characteristics, such as area and elevation, are also likely to be important factors that mediate specific island responses to drivers of change.     

Restitution of granule stores in the rabbit parotid gland after isoprenaline-induced secretion

Summary A detailed stereological analysis has been made of the organelle content of rabbit acinar cells during the restoration of granule stores following extensive degranulation with isoprenaline (IPR). Rabbits were sacrificed 2, 4, 8, 12 and 16 h after IPR administration and the volumes and proportions of intracellular organelles were compared with those of untreated glands.At 2 h only 5% of cell volume was occupied by secretion granules, but there was already evidence of nascent granule formation. The volume per cell of secretion granules increased in sigmoid fashion and by 16 h amounted to 350 m³/cell, 36% of cell volume, which are values similar to those of the control replete glands. IPR treatment caused some initial swelling of the cells, and there were transient increases in the volumes of several compartments. However, the volume of mitochondrial and lysosomal compartments had returned to control levels by 4 h and that of the nucleus by 8 h. The greatest increase was in the volume of the rough endoplasmic reticulum which had increased by nearly 70% by 2 h and remained enlarged throughout the period of restitution. However, neither the volume nor the proportion of the smooth membraned compartment varied throughout the period of analysis.The results are analysed in the light of the overall response of the cells to IPR and the interaction of the organelles during the synthetic phase of the secretory cycle. They are presented as a basis for ensuing studies of the granule populations and the membrane composition of the cells during the restoration of granule stores.     

Accuracy of neuronal interspike times calculated from a diffusion approximation

The theory of neuronal firing in Stein's model is outlined as well as the corresponding theory for a diffusion approximation which has the same first two infinitesimal moments. The diffusion approximation is derived from the discontinuous model in the limit of large input frequencies and small postsynaptic potential amplitudes. A comparison of the calculated mean interspike intervals is made for various values of the threshold for firing and various input frequencies. The diffusion approximation can underestimate the interspike interval by up to 100% or severely overestimate it, depending on the input frequencies and the threshold. A general relation between the predictions of the two models is deduced.     

On the chromatographic heterogeneity of human fetal hemoglobin.

Minor fetal hemoglobins in red cell hemolysates of newborn and adults with elevated levels of Hb F have been separated and quantitated by Biorex 70 column chromatography. In addition to Hb F1, other minor hemoglobin zones eluting before F1, pre-F1, and after F1, post-f1 have been observed. The relative amounts of the two pre-F1 zones and F1 are higher in the red cells of adults with 97--100% Hb F (homozygous hereditary persistence of fetal hemoglobin, homozygous deltabeta-thalassemia and homozygous beta0-thalassemia) than in the red cells of an adult with homozygous beta+-thalassemia with 66% Hb F, a child with a trisomy-D-13 having 38% Hb F, and in two newborn. Hb F was glycosylated in vitro with [14C]glucose or [14C] glucose 6-phosphate, and was acetylated using chicken reticulocyte lysate or a crude acetyltransferase preparation isolated from the same lysate with [14C]acetyl-CoA as substrate. Chromatographic analyses indicated that the Hb F1 zone can be formed both by glycosylation and acetylation of Hb F, and that pre-F1 zones can be products of the reaction of Hb F with phosphorylated glycolytic intermediates. Biosynthesis of minor hemoglobins in reticulocytes was studied with [14C]leucine in the presence and absence of cycloheximide and by pulse-chase. The resulting data indicate that Hb F1 synthesis is dependent upon Hb F synthesis and that the posttranslational modification may take place at an early stage in Hb F synthesis.