Occurrence of phosphorus and its potential remohilization in the littoral sediments of a productive English lake

SUMMARY. 1. Vertical profiles of pH were measured at nine shallow water (<5m) locations in Esthwaite Water. These indicate strong gradients of pH near the sediment water interface suggesting a marked buffering capacity of the sediments.
2. Thirteen littoral sediment cores were horizontally sectioned and sequentially extracted (0.5 M NaHCO₃, 0.1 M NaOH, 1 M HCI) and analysed for soluble reactive phosphorus. The core sections were also analysed for total phosphorus and per cent organic content to determine the vertical and areal variability of phosphorus within the littoral sediments of Esthwaite Water.
3. The rate of release of phosphorus from intact sediment cores was measured in the laboratory as a function of the pH of overlying water, yielding the relationship log K=0.54 pH−3.94, K=mg Pm⁻²day⁻¹. The maximum release rate measured was 75 mg P m⁻² day⁻² at pH = 10.5.
4. Experiments on sediment slurries indicate that the release of phosphorus at pH 10 is rapid with approximately 50% of the total NaHCO₃+ NaOH extractable phosphorus being released within 3 h.
5. Phosphorus release from the littoral sediments may equal or exceed external sources plus hypolimnetic inputs during periods of high pH associated with times of maximum algal biomass.     

Trypanosoma pacifica sp. n. from the English Sole Parophrys vetulus Girard from Oregon*

Trypanosoma pacifica sp. n. is described from the blood of the English sole, Parophrys vetulus Girard, from Oregon. The total length averages 35.9 μm of which 15.4 μm is free flagellum. Comparisons are made with other trypanosomes reported from related species of fishes and with those reported from marine fishes adjacent to North America.     

The Location of Glutamine Synthetase in Leaf Cells and its Role in the Reassimilation of Ammonia Released in Photorespiration

The localization of glutamine synthetase within the cells ofbarley and pea leaves has been reinvestigated using either amechanical technique or rupturing of isolated protoplasts torelease the cellular organelles, and both differential and densitygradient centrifugation to separate them. In no case could wefind evidence for any significant association between glutaminesynthetase and the mitochondria; our results suggest that theenzyme is present in the chloroplast and the cytoplasm of bothspecies. Experiments with isolated mitochondria from spinachalso failed to provide any suggestion that these organellesmight contain glutamine synthetase. Thus there is no evidenceto support the hypothesis, published by others, that mitochondriareassimilate ammonia, released from glycine oxidation, by meansof their own glutamine synthetase. Further experiments werecarried out to see if glutamate dehydrogenase present in themitochondria could reassimilate ammonia under conditions inwhich the electron transport chain to oxygen was blocked. Althoughthere was some evidence for a small amount of assimilatory glutamatedehydrogenase activity under these conditions it was dependenton adding relatively high concentrations of ammonia and wasinsufficient to sustain the rate of recycling of NAD requiredfor glycine oxidation. The results were thus considered to becompatible with the operation of the photorespiratory nitrogencycle as previously published.     

Nyssidium jiayinense sp. no v. (Cercidiphyllaceae) of the Early Tertiary from north-east China

Nyssidium jiayinense , a new species of the extinct genus JSyssidium , Cercidiphyllaceae, is described from the Palaeocene of north-east China. The infructescences of the fossil are paniculate with 14–22 follicles in individual racemose branches. The follicles occur in pairs with opposite ventral sutures. The follicle wall is three-layered, with a thin epidermis. Mesocarp fibres are longitudinal and endocarp fibres transverse. The distinct features of the infructescence structure differ from all other fossil Cercutiphyllum-like plants and living Cercidiphyllum . The fossil provides new morphological evidence supporting the hypothesis that the follicle clusters in extant Cercidiphyllum evolved by reduction from an elongated inflorescence.     

Chondrichthyan‐like scales from the Middle Ordovician of Australia

Abstract: Microvertebrate sampling of the Stairway Sandstone (Darriwilian, Middle Ordovician, central Australia) has yielded scales that are chondrichthyan‐like in their overall construction, and Tantalepis gatehousei gen. et sp. nov. is erected here to describe these specimens. Tantalepis gatehousei gen. et sp. nov. is the stratigraphically oldest microsquamous taxon described thus far, and the ‘shark‐like’ appearance of the scales may extend the chondrichthyan lineage back into the Middle Ordovician. The presence of ‘shark‐like’ scales in the fossil record some 50 myr prior to the first articulated chondrichthyan body fossils and 44 myr before the first clearly identifiable chondrichthyan teeth suggests there is a considerable scope for the recovery of articulated specimens with which to document the early history of crown gnathostomes. Traditional hypotheses of phylogenetic relationships among early jawed vertebrates were recently challenged by the proposal of a radically different tree topology. However, the development of a new data set specifically addressing scale‐based characters is required before taxa such as Tantalepis, that are based upon disarticulated remains alone, can be firmly placed within the emerging, revised, evolutionary narrative.     

Ecological and evolutionary factors in the morphological diversification of South American spiny rats

Understanding the processes underlying morphological diversification is a central goal in ecology and evolutionary biology and requires the integration of information about phylogenetic divergence and ecological niche diversity. In the present study, we use geometric morphometrics and comparative methods to investigate morphological diversification in Neotropical spiny rats of the family Echimyidae. Morphological diversification is studied as shape variation in the skull, comprising a structure composed of four distinct units: vault, base, orognathofacial complex, and mandible. We demonstrate association among patterns of variation in shape in different cranial units, levels of phylogenetic divergence, and ecological niche diversification. At the lower level of phylogenetic divergence, there is significant and positive concordance between patterns of phylogenetic divergence and cranial shape variation in all cranial units. This concordance may be attributable to the phylogenetic and shape distances being calculated between species that occupy the same niche. At higher phylogenetic levels of divergence and with ecological niche diversity, there is significant concordance between shape variation in all four cranial units and the ecological niches. In particular, the orognathofacial complex revealed the most significant association between shape variation and ecological niche diversity. This association may be explained by the great functional importance of the orognathofacial complex.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 646–660.     

ORDOVICIAN FISH FROM THE ARABIAN PENINSULA

Abstract:  Over the past three decades Ordovician pteraspidomorphs (armoured jawless fish) have been recorded from the fringes of the Gondwana palaeocontinent, in particular Australia and South America. These occurrences are dominated by arandaspid agnathans, the oldest known group of vertebrates with extensive biomineralisation of the dermoskeleton. Here we describe specimens of arandaspid agnathans, referable to the genus Sacabambaspis Gagnier, Blieck and Rodrigo, from the Ordovician of Oman, which represent the earliest record of pteraspidomorphs from the Arabian margin of Gondwana. These are among the oldest arandaspids known, and greatly extend the palaeogeographical distribution of the clade around the periGondwanan margin. Their occurrence within a very narrow, nearshore ecological niche suggests that similar Middle Ordovician palaeoenvironmental settings should be targeted for further sampling.