The cost of sex revisited: effects of male gamete output of hermaphrodites that are asexual in their female capacity

The genetic cost of sexual reproduction has been attributed to two causes in mathematical formulations: male function or genome dilution. We develop and analyse a genetic model that shows that both costs occur, depending upon the conditions. The model differs from previous formulations in that the level of output and fertilization success of male gametes produced by hermaphrodites that are asexual in their female function (henceforth "parthenogenetic hermaphrodites") are treated as variables, rather than constants fixed at 0 or 1, as has previously been the case. By expressing the cost of sex in terms of per capita egg loss of sexual individuals and parthenogenetic hermaphrodites, we partition the cost into components due to male function and genome dilution. Which component dominates the cost of sex depends upon the relative male gamete output of the parthenogenetic hermaphrodites. The cost of sex is observed to increase, or remain unchanged in some marginal cases, with increases in (i) frequency of parthenogenetic hermaphrodites, (ii) fertilization success of male gametes produced by parthenogenetic hermaphrodites and (iii) potential eggs lost by diverting resources to male gamete production. In certain situations, parthenogenetic hermaphrodites with an intermediate level of male gamete output have the greatest fitness advantage over sexual individuals. If heritable variation for levels of male gamete output exists among parthenogenetic hermaphrodites, this raises the possibility of the evolution of optimal levels of male gamete production by parthenogenetic hermaphrodites through natural selection, in situations of recurring invasion of asexual populations by propagules from sexual populations, a scenario that is increasingly being appreciated as potentially fairly likely to occur in nature.     

Proline isomerization-independent accumulation of an early intermediate and heterogeneity of the folding pathways of a mixed alpha/beta protein, Escherichia coli thioredoxin

Oxidized Escherichia coli thioredoxin (Trx) is a small protein of 108 residues with one disulfide bond (C32-C35 essentially involved in the activity) and no prosthetic moieties, which folds into a structural motif containing a central twisted beta-sheet flanked by helices that is found in many larger proteins. The kinetics of refolding of Trx in vitro have been investigated using a newly developed active site titration assay and continuous or stopped-flow (SF) methods in conjunction with circular dichroism (CD) and fluorescence (Fl) spectroscopy. These studies revealed the presence of early folding intermediates with "molten globule or pre-molten globule" characteristics. Measurements of the ellipticity at 222 nm indicated that about 68% of the total change associated with refolding occurred during the dead time (4 ms) of the stopped-flow instrument, suggesting the formation of substantial secondary structure. The reconstruction of the far-UV CD spectrum of the burst intermediate using combined continuous and stopped-flow methods showed the formation of a defined secondary structure that contains more beta-structure than the native state. Kinetic measurements using SF far-UV CD and Fl over a wide range (0.087-6 M) of GuHCl concentrations at two temperatures (6 and 20 degreesC) demonstrated that the population formed during the 4 ms dead time contained multiple species that are stabilized mainly by hydrophobic interactions and undergo further folding along alternative pathways. One of these species leads directly and rapidly to the native state as demonstrated by active site titration, while the two others fold into a fourth intermediate that is slowly converted to the native protein. Double-jump experiments suggest that the heterogeneity in folding behavior results from proline isomerizations occurring in the unfolded state. Conversely, the accumulation of the burst intermediate does not depend on proline isomerizations.     

Noise detection during bradycardia pacing with a hybrid nonthoracotomy implantable cardioverter defibrillator system: incidence and clinical significance

The purpose of this study was to prospectively evaluate the incidence of noise detection during bradycardia pacing by an FDA approved hybrid nonthoracotomy ICD system. An illustrative case report which prompted this investigation is provided. Backup bradycardia pacing by tiered therapy cardioverter defibrillators has been useful in preventing postshock bradycardia and occasionally for chronic rate support in bradycardic patients. Unexplained "noise" detected by real-time telemetry has been previously described during bradycardia pacing by a device utilizing automatic gain control for sensing. Eighteen patients were prospectively evaluated for noise detection during ventricular pacing by the ICD. Real-time telemetry was analyzed with each patient: (1) supine, (2) supine with deep inspiration/expiration, (3) supine during Valsalva, and (4) during a change in position from supine to sitting. Analysis of pacing threshold and lead impedance was made in each patient. Eleven of 18 patients had noise detected on real-time telemetry during bradycardia pacing. In 10 patients this was noted during deep inspiration/expiration, in 2 during Valsalva maneuver, and in 5 with position change. There was no evidence in any patient of lead malfunction nor any difference in pacing threshold or lead impedance between patients with noise detected versus those without it. Noise detection by an approved hybrid ICD system is common and may be due to the automatic gain control which maximizes sensitivity during bradycardia pacing. This may lead to clinically significant events, with both suppression of bradycardia pacing and triggering of tachycardia therapy in the absence of ventricular tachyarrhythmias in pacemaker-dependent patients.     

Comparison of bond strengths of three denture base resins to treated nickel-chromium-beryllium alloy

The success of radiotherapy in eradicating tumours depends on the total radiation dose, but what limits this dose is the tolerance of the normal tissues within the treatment volume. Studies involving fibroblast survival have demonstrated the theoretical feasibility of a predictive assay of radiation sensitivity, but such an assay is still far from clinical application. Using pulsed-field gel electrophoresis (PFGE), we have quantified the initial "apparent" number of DNA double-strand breaks (dsb) induced by the radiation as an alternative measure of sensitivity in 2 different normal cell types from the same patients, epidermal skin cells and lymphocytes. We found significant inter-individual variation in the measured dsb (1-5 dsb/Gy/DNA unit). We also found a linear correlation between molecular damage in lymphocytes and skin samples from the same patient (slope = 0.83; r = 0.694; p = 0.0001). These results suggest that the initial number of dsb could be used as an indicator of the in vivo response to radiation.     

Development and fine structure of murine Purkinje cells in dissociated cerebellar cultures: dendritic differentiation, synaptic maturation, and formation of cell-class specific features

Cerebellar Purkinje cells (PC) display a highly distinctive form of polarity. We have cultured murine PCs from dissociated E16 cerebellar anlagen for 1 week to investigate the early stages of neuronal compartmentalization and synaptic interactions, features which are important for the establishment of neuronal polarity. To unequivocally identify the PCs we utilized light and electron microscopic immunocytochemistry with an anti-serum to the cell class-specific marker L7/pcp2 gene product. The PCs typically show a single, long axon, numerous short appendages classified as filopodia and protospines, and a small number of protodendrites. The nucleus is positioned asymmetrically in both the horizontal and vertical axes of the soma. The Golgi apparatus, coated and uncoated vesicles, and mitochondria are prominent ultrastructural features, while the endoplasmic reticulum is highly fragmented. The cell body receives rudimentary synapses on its smooth surfaces and appendages and no consistent morphological differences were detected between these elementary contacts. The axon is clearly identifiable; it emanates from either the cell body or a protodendrite, bifurcates at predominantly right angles, forms beaded collaterals, and terminates with relatively large growth cones. The varicosities of the PC axon contain pleomorphic synaptic vesicles and form rudimentary synapses primarily with the dendritic shafts of immunonegative neurons. The protodendrites are short, quickly tapering and sparsely branched; they emit numerous filopodia and immature spines and terminate with small growth cones. Rudimentary synapses are received on the proximal dendritic shafts and filopodia, and more mature synapses occur frequently on protospines. With few exceptions, PCs lie atop an astrocytic bed layer and glial processes are apposed to the various aspects of the PC body left free by the afferent axons. By contrast, PC processes are largely free of glial sheaths. We conclude that the "stellate stage" of PC development in situ is replicated rather faithfully in culture and that PCs have established polarity and have begun to form intercellular contacts by 1 week in vitro. Moreover, the PCs are already morphologically distinct from other cell types in the 1 week cultures, although they have yet to develop the differentiated features that distinguish mature PCs.     

Laparoscopic versus open appendectomy

BACKGROUND: Clinical manifestations and course of sickle-cell anemia are variable. Knowledge about the factors, possibly geographic, that influence prognosis are still scanty. POPULATION AND METHODS: Data of hospitalization and management of children with sickle-cell disease were studied during two years (1992-1993) in the Pediatric Unit of Libreville Hospital. They concerned 205 admissions of 171 children and 131 outpatients. RESULTS: The main causes of hospitalization were: acute anemia (36 cases before the age of 5 years); painful crisis whose frequency increased with age (23% before 5 years, 35% between 5 and 10, 42% after 10 years); infections, essentially pulmonary occurring early, and bone infections at any age. Eight children died (because a complication of their disease). Among the 131 outpatients, half were detected because pyrexia, anemia and/or more often "hand-foot syndrome". More than 60% had hepatomegaly, one third still had splenomegaly after five years of age and more than one third was icteric. More than half children older than ten years had growth disorders. Mean hemoglobin level was 7 g/dL. 21 of the 83 tested children for HBsAg were positive and only one out of 79 was positive for HIV. CONCLUSIONS: Clinical manifestations and course of sickle-cell anemia in our patients are similar to those reported in Congolese children. Genetic and environmental factors may be responsible for differences with children from other, in particular French, cohorts.     

一种改进的TCP拥塞控制算法

TCP Reno拥塞控制机制是目前互联网中采用的主流拥塞控制算法.根据TCP Reno实现拥塞避免与拥塞控制的AIMD算法中加性因子与减性因子过于武断,对可用带宽的探测缺乏细分,造成信道利用率未达合理水平等缺陷,为此,提出一种根据拥塞窗口的增长情况进行更为平滑的信道容量探测算法,采用基于对数的增长算法和下降算法,通过N...     

基于Lotus Notes的分布式信息商函系统的设计与实现

设计并实现了一种基于Ｌｏｔｕｓ Ｎｏｔｅｓ的分布式信息邮政商业信函系统,并研究了系统实现过程中的两个关键技术。     

Prophylactic efficacy of tilmicosin for bovine respiratory tract disease

The prophylactic administration of injectable tilmicosin for pneumonia in weaned beef calves was investigated in 1,806 animals. Comparisons were made among calves receiving an "on-arrival" injection of tilmicosin, calves receiving a single injection of long-acting oxytetracycline, and calves receiving no prophylaxis. Morbidity and mortality attributable to pneumonia, morbidity and mortality attributable to all causes, and case fatality were significantly lower in the group of calves that received tilmicosin, compared with calves that received long-acting oxytetracycline and calves that received no prophylactic antibiotic. Mean time to initial pneumonia treatment was significantly extended in calves that received prophylaxis, compared with those that received no antibiotic on arrival at the feedlot. Calves that received tilmicosin gained significantly more weight than calves that received oxytetracycline. Calves that were not treated for pneumonia during the trial period gained significantly more weight than did those calves that were treated for pneumonia regardless of experimental group. The majority of mortalities were attributable to fibrinous pneumonia (31/34). Important bacterial isolates (Pasteurella spp, Haemophilus somnus, Actinomyces pyogenes) obtained at necropsy did not have resistance to tilmicosin in association with administration of tilmicosin as prophylaxis for pneumonia. However, bacterial resistance to trimethoprim/sulfonamide and to oxytetracycline were commonly found in these postmortem isolates.     

Anion modulation of taste responses in sodium-sensitive neurons of the hamster chorda tympani nerve

Beidler's work in the 1950s showed that anions can strongly influence gustatory responses to sodium salts. We have demonstrated "anion inhibition" in the hamster by showing that the chorda tympani nerve responds more strongly to NaCl than to Na acetate over a wide range of concentrations. Iontophoretic presentation of Cl- and acetate to the anterior tongue elicited no response in the chorda tympani, suggesting that these anions are not directly stimulatory. Drugs (0.01, 1.0, and 100 microM anthracene-9-carboxylate, diphenylamine-2-carboxylate, 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonate, and furosemide) that interfere with movements of Cl- across epithelial cells were ineffective in altering chorda tympani responses to 0.03 M of either NaCl or Na acetate. Anion inhibition related to movements of anions across epithelial membranes therefore seems unlikely. The chorda tympani contains a population of nerve fibers highly selective for Na+ (N fibers) and another population sensitive to Na+ as well as other salts and acids (H fibers). We found that N fibers respond similarly to NaCl and Na acetate, with spiking activity increasing with increasing stimulus concentration (0.01-1.0 M). H fibers, however, respond more strongly to NaCl than to Na acetate. Furthermore, H fibers increase spiking with increases in NaCl concentration, but generally decrease their responses to increasing concentrations of Na acetate. It appears that anion inhibition applies to taste cells innervated by H fibers but not by N fibers. Taste cells innervated by N fibers use an apical Na+ channel, whereas those innervated by H fibers may use a paracellularly mediated, basolateral site of excitation.