Molting fluid enzymes of the tobacco hornworm,Manduca sexta: Timing of proteolytic and chitinolytic activity in relation to pre-ecdysial development

Developmental profiles for a number of molting fluid (MF) enzyme activities were established and related to the progress of pupal cuticle degradation during the four days that precede the eclosion of adult tobacco hornworms. Cuticle degrading activity, molting fluid protease 1 (MFP-1), and molting fluid protease 2 (MFP-2) all increased in activity at the time that loss of material from the old cuticle occurred. In contrast, chitinase and β-acetylglucosaminidase activities did not parallel weight loss from the old cuticle. These results are consistent with the hypothesis that proteolytic activity is a prerequisite for the action of chitinase on cuticle chitin. © 1993 Wiley-Liss, Inc.     

Canopy tree mortality depends on the proportion of crown exposed to sunlight,but this effect varies with species' wood density

Understanding what drives changes in tree mortality as well as the covariates influencing trees' response is a research priority to predict forest responses to global change. Here, we combined drone photogrammetry and ground-based data to assess the influence of crown exposure to light (relative to total crown area), growth deviations (relative to conspecifics), tree size, and species' wood density (as a surrogate for light-demanding and shade-tolerant life-history strategies) on the mortality of 984 canopy trees in an Amazon terra firme forest. Trees with lower wood density were less prone to die when their proportion of crown was more exposed to sunlight, but this relationship with relative crown exposure weakened and slightly reversed as wood density increased. Trees growing less than their species average had higher mortality, especially when the species' wood density decreased. The role of wood density in determining the survival of canopy trees under varying light conditions indicates differential responses of light-demanding versus shade-tolerant species. Our results highlight the importance of accounting for life-history strategies, via plant functional types, in vegetation dynamic models aiming to predict forest demography under a rapidly changing climate. Abstract in Spanish is available with online material.     

Chromosomal localization of uroplakin genes of cattle and mice

The asymmetric unit membrane (AUM) of the apical surface of mammalian urinary bladder epithelium contains several major integral membrane proteins, including uroplakins IA and IB (both 27 kDa), II (15 kDa), and III (47 kDa). These proteins are synthesized only in terminally differentiated bladder epithelial cells. They are encoded by separate genes and, except for uroplakins IA and IB, appear to be unrelated in their amino acid sequences. The genes encoding these uroplakins were mapped to chromosomes of cattle through their segregation in a panel of bovine x rodent somatic cell hybrids. Genes for uroplakins IA, IB, and II were mapped to bovine (BTA) Chromosomes (Chrs) 18 (UPK1A), 1 (UPK1B), and 15 (UPK2), respectively. Two bovine genomic DNA sequences reactive with a uroplakin III cDNA probe were identified and mapped to BTA 6 (UPK3A) and 5 (UPK3B). We have also mapped genes for uroplakins 1A and II in mice, to the proximal regions of mouse Chr 7 (Upk1a) and 9 (Upk2), respectively, by analyzing the inheritance of restriction fragment length variants in recombinant inbred mouse strains. These assignments are consistent with linkage relationships known to be conserved between cattle and mice. The mouse genes for uroplakins IB and III were not mapped because the mouse genomic DNA fragments reactive with each probe were invariant among the inbred strains tested. Although the stoichiometry of AUM proteins is nearly constant, the fact that the uroplakin genes are unlinked indicates that their expression must be independently regulated. Our results also suggest likely positions for two human uroplakin genes and should facilitate further analysis of their possible involvement in disease.     

XYLEM WATER HOLDING CAPACITY AS A SOURCE OF ERROR IN WATER POTENTIAL ESTIMATES MADE WITH THE PRESSURE CHAMBER AND THERMOCOUPLE PSYCHROMETER

The pressure chamber and the thermocouple psychrometer often provide different values when used to estimate plant water potential. One hypothesis to explain the discrepancy between instruments is that water movement between the xylem and symplast occurs during pressurization in the pressure chamber. Pressure chamber and thermocouple psychrometer measurements of Pinus ponderosa (Laws.) seedling shoots and mature Quercus agrifolia (Nee) shoots showed that the discrepancy is greater for Quercus. It was hypothesized that the xylem water content-water potential relationship of these species would explain the magnitude of the discrepancy between instruments. The xylem water holding capacity alone, however, does not explain the difference between species. The larger discrepancy in Quercus is likely due to a greater volume of water held in the xylem relative to the volume held in the symplast.     

Frequent nest relocation in the ant Aphaenogaster araneoides: resources, competition, and natural enemies

Sessile and vagile organisms differ from one another in some fundamental ways, including methods of resource acquisition and competition. Ant colonies are typically studied as sessile entities, even though a large fraction of ant species frequently relocate their nests in the course of their life history. Little is known about the causes and consequences of nest relocation, but it is likely that the costs and benefits of relocation are driven by nest quality, neighborhood competition, or resource availability. In this paper, we document several cycles of nest relocation in a population of the Central American ant Aphaenogaster araneoides . In our first experiment, we tracked the pattern of relocation, testing whether environmental characteristics and colony demography were associated with relocation behavior. In our second experiment, we manipulated resource availability by adding or subtracting leaf litter, which is known to predict colony growth. We found that colonies relocated their nests once per week on average and colonies often reoccupied nests from which they had once emigrated. Larger colonies relocated more frequently than smaller colonies, and quickly growing colonies utilized a greater number of nests within their home range compared to slowly growing colonies. Relocation events were most likely to occur in periods when vapor pressure deficits were greatest. Nearest neighbor distance and other measures of environmental conditions were not associated with relocation behavior and there was no significant effect of litter removal or supplementation. We found evidence that multiple natural enemies attacked A. araneoides colonies. Based on the demographic correlates of relocation and our rejection of other plausible hypotheses, we propose that nest relocation is driven by the escape from natural enemies.     

Inadequate rates are lower when FNAC samples are taken by cytopathologists

Inadequate rates (IR) in FNAC from different sources were compared. The rates were lowest when FNAC was performed by a cytopathologist (12%) and highest when done by a non-cytopathologist (32%). These differences were mirrored in high IRs in breast cancer cases. IR was not significantly improved when non-cytopathologist FNAC was attended by a cytotechnician.     

Estimating dataset size requirements for classifying DNA microarray data.

A statistical methodology for estimating dataset size requirements for classifying microarray data using learning curves is introduced. The goal is to use existing classification results to estimate dataset size requirements for future classification experiments and to evaluate the gain in accuracy and significance of classifiers built with additional data. The method is based on fitting inverse power-law models to construct empirical learning curves. It also includes a permutation test procedure to assess the statistical significance of classification performance for a given dataset size. This procedure is applied to several molecular classification problems representing a broad spectrum of levels of complexity.     

Identification of a Novel Cryptosporidium Genotype in Pigs

Over a 3-year period, a total of 646 fecal samples from pigs in 22 indoor and outdoor herds from Western Australia were screened for Cryptosporidium spp. by microscopy. Results revealed that 39 of 646 samples (6.03%) were positive for Cryptosporidium. Cryptosporidium was much more common in outdoor herds (17.2%) than in indoor herds (0.5%) and was more common in animals between the ages of 5 and 8 weeks (69.2%) than in younger animals (P < 0.0001). Molecular characterization of the positive samples at the 18S ribosomal DNA locus identified two distinct genotypes of Cryptosporidium: the previously identified pig genotype I and a novel pig genotype (pig genotype II), both of which warrant species status.