Interspecific mate choice by late-courting male western grebes

In mixed populations of western and Clark's grebes, advertisingcalls by males and females play a critical role in mate choiceand reproductive isolation. We conducted field playback experimentsthat tested whether courting western grebe males became lesschoosy in their responses to female Clark's grebe calls as themating season progressed and mating opportunities diminished.Late-courting western grebe males were much more likely to answerand approach advertising calls of Dark's grebe females thanwere males courting earlier in the season. This change in responsivenessoccurred as the operational sex ratio index of the populationapproached 3:1 male calls per female call. These and field censusdata support the hypothesis that late-season hybridization betweenthese two closely related species may be a result not of speciesmisidentification, but of active and adaptive mate choice byindividuals with limited alternatives.     

Phenology and Stem Diameter Increment Seasonality in a Costa Rican Wet Tropical Forest

The relationship between phenology and tree stem diameter increment is largely unexplored in tropical species, especially in wet tropical forests. To explore links between these phenomena, we measured stem diameter increment and phenology of ten canopy tree species from a range of functional types in the Atlantic lowlands of Costa Rica to test for seasonal and interannual patterns. We measured stem diameter increment using band dendrometers and visually assessed leaf and reproductive phenology monthly from 1997 to 2000. We categorized the species into groups based on patterns of leaf exchange and reproduction. Species were either deciduous with synchronous or asynchronous leaf drop, or evergreen with continuous or seasonal leaf flushing. Flowering occurred supra-annually, annually, or continuously. Of the ten species studied, four species, Cecropia insignis, Dipteryx panamensis, Lecythis ampla, and Simarouba amara , had consistent seasonal stem diameter increment patterns in both years. Dipteryx panamensis and L. ampla were deciduous with synchronized leaf drop . Cecropia insignis was evergreen and produced new leaves continuously. Simarouba amara , also evergreen, exchanged leaves over a brief period once a year. We tested whether stem diameter increment was correlated to phenology using logistic regression. Leaflessness significantly explained patterns in stem diameter increment but reproductive phenology did not. Deciduous trees were 2.6–9.3 times more likely to grow less than average the month following leaffall than in months when trees had full crowns.     

Molecular genetic study of human arginase deficiency

We have explored the molecular pathology in 28 individuals homozygous or heterozygous for liver arginase deficiency (hyperargininemia) by a combination of Southern analysis, western blotting, DNA sequencing, and PCR. This cohort represents the majority of arginase-deficient individuals worldwide. Only 2 of 15 homozygous patients on whom red blood cells were available had antigenically cross-reacting material as ascertained by western blot analysis using anti-liver arginase antibody. Southern blots of patient genomic DNAs, cut with a variety of restriction enzymes and probed with a near-full-length (1,450-bp) human liver arginase cDNA clone, detected no gross gene deletions. Loss of a TaqI cleavage site was identified in three individuals: in a homozygous state in a Saudi Arabian patient at one site, at a different site in homozygosity in a German patient, and in heterozygosity in a patient from Australia. The changes in the latter two were localized to exon 8, through amplification of this region by PCR and electrophoretic analysis of the amplified fragment after treatment with TaqI; the precise base changes (Arg291X and Thr290Ser) were confirmed by sequencing. It is interesting that the latter nucleotide variant (Thr290Ser) was found to lie adjacent to the TaqI site rather than within it, though whether such a conservative amino acid substitution represents a true pathologic mutation remains to be determined. We conclude that arginase deficiency, though rare, is a heterogeneous disorder at the genotypic level, generally encompassing a variety of point mutations rather than substantial structural gene deletions.     

RAGE mediates amyloid-beta peptide transport across the blood-brain barrier and accumulation in brain

Amyloid-beta peptide (Abeta) interacts with the vasculature to influence Abeta levels in the brain and cerebral blood flow, providing a means of amplifying the Abeta-induced cellular stress underlying neuronal dysfunction and dementia. Systemic Abeta infusion and studies in genetically manipulated mice show that Abeta interaction with receptor for advanced glycation end products (RAGE)-bearing cells in the vessel wall results in transport of Abeta across the blood-brain barrier (BBB) and expression of proinflammatory cytokines and endothelin-1 (ET-1), the latter mediating Abeta-induced vasoconstriction. Inhibition of RAGE-ligand interaction suppresses accumulation of Abeta in brain parenchyma in a mouse transgenic model. These findings suggest that vascular RAGE is a target for inhibiting pathogenic consequences of Abeta-vascular interactions, including development of cerebral amyloidosis.     

Human papillomavirus is associated with monoclonal gammopathies of unknown significance

When monoclonal gammopathies arise in persons without evidence of plasma cell malignancy or lymphoproliferative disease, the term monoclonal gammopathy of unknown significance (MGUS) can be used. MGUS is believed to be the preneoplastic phase of lymphoproliferative diseases because many of these patients eventually develop malignant disease, mainly multiple myeloma. We have previously identified human papillomavirus (HPV) in a chronic benign plasma cell tumor of the cervix and in the bone marrow of multiple-myeloma patients. In the following study, we expanded upon our initial observation by analyzing 14 patients with MGUS. Bone marrow biopsies of the patients were analyzed for HPV sequences using polymerase chain reaction (PCR) and in situ hybridization. Normal controls included 26 bone marrow specimens, 24 analyzed by PCR and two by in situ hybridization. A significant association was found to exist between HPV and MGUS (p=0.001). Among 14 patients iwth MGUS, HPV sequences have been identified in 10 of the bone marrow biopsies. These results suggest that HPV can reside in the bone marrow of a premalignant lymphoproliferative disease.     

Association between tree-ring and needle δ<Superscript>13</Superscript>C and leaf gas exchange in <Emphasis Type="Italic">Pinus halepensis</Emphasis> under semi-arid conditions

Associations between δ¹³C values and leaf gas exchanges and tree-ring or needle growth, used in ecophysiological compositions, can be complex depending on the relative timing of CO₂ uptake and subsequent redistribution and allocation of carbon to needle and stem components. For palaeoenvironmental and dendroecological studies it is often interpreted in terms of a simple model of δ¹³C fractionation in C₃ plants. However, in spite of potential complicating factors, few studies have actually examined these relationships in mature trees over inter- and intra-annual time-scales. Here, we present results from a 4 years study that investigated the links between variations in leaf gas-exchange properties, growth, and dated δ¹³C values along the needles and across tree rings of Aleppo pine trees growing in a semi-arid region under natural conditions or with supplemental summer irrigation. Sub-sections of tissue across annual rings and along needles, for which time of formation was resolved from growth rate analyses, showed rapid growth and δ¹³C responses to changing environmental conditions. Seasonal cycles of growth and δ¹³C (up to ~4‰) significantly correlated (P<0.01) with photosynthetically active radiation, vapour pressure deficit, air temperature, and soil water content. The irrigation significantly increased leaf net assimilation, stomatal conductance and needle and tree-ring growth rate, and markedly decreased needle and tree-ring δ¹³C values and its sensitivity to environmental parameters. The δ¹³C estimates derived from gas-exchange parameters, and weighted by assimilation, compared closely with seasonal and inter-annual δ¹³C values of needle- and tree-ring tissue. Higher stomatal conductances of the irrigated trees (0.22 vs. 0.08 mol m⁻² s⁻¹ on average) corresponded with ~2.0‰ lower average δ¹³C values, both measured and derived. Derived and measured δ¹³C values also indicated that needle growth, which occurs throughout the stressful summer was supported by carbon from concurrent, low rate assimilation. For Aleppo pine under semi-arid and irrigated conditions, the δ¹³C of tree-ring and needle material proved, in general, to be a reasonable indicator of integrated leaf gas-exchange properties.