Degree Of Starvation Research Articles

Correlating biodegradation kinetics of 2,3,7,8-tetrachlorodibenzo-p-dioxin to the dynamics of microbial communities originating from soil in Vietnam contaminated with herbicides and dioxins.

We studied the succession of bacterial communities during the biodegradation of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). The communities originated from a mesocosm with soil from Bien Hoa airbase in Vietnam heavily contaminated with herbicides and dioxins. They were grown in defined media with different carbon and Gibbs energy sources and 2,3,7,8-TCDD. Cultures with dimethyl sulfoxide (DMSO) as the sole carbon and energy source degraded about 95% of 2,3,7,8-TCDD within 60 days of cultivation. Those with an additional 1 mM of vanillin did that in roughly 90 days. Further 16S rRNA gene amplicon sequencing showed that the increase in relative abundance of members belonging to the genera Bordetella, Sphingomonas, Proteiniphilum, and Rhizobium correlated to increased biodegradation of 2,3,7,8-TCDD in these cultures. A higher concentration of vanillin slowed down the biodegradation rate. Addition of alternative carbon and Gibbs energy sources, such as amino acids, sodium lactate and sodium acetate, even stopped the degradation of 2,3,7,8-TCDD completely. Bacteria from the genera Bordetella, Achromobacter, Sphingomonas and Pseudomonas dominated most of the cultures, but the microbial profiles also significantly differed between cultures as judged by non-metric multidimensional scaling (NMDS) analyses. Our study indicates that 2,3,7,8-TCDD degradation may be stimulated by bacterial communities preadapted to a certain degree of starvation with respect to the carbon and energy source. It also reveals the succession and abundance of defined bacterial genera in the degradation process.

In-Session-Reflective-Functioning in Anorexia Nervosa: An Analysis of Psychotherapeutic Sessions of the ANTOP Study.

ObjectivePrevious research suggests that patients with anorexia nervosa (AN) show an impaired capacity to mentalize (reflective functioning, RF). RF is discussed as a possible predictor of outcome in psychotherapeutic processes. The study aimed to explore RF in sessions of patients with AN and its association with outcome and type of treatment.MethodsA post-hoc data analysis of selected cases from a randomized trial on outpatient psychotherapy for AN was conducted. Transcripts from 84 sessions of 28 patients (early phase, middle phase, and end of treatment) were assessed using the In-Session-Reflective-Functioning-Scale [14 cognitive-behavior therapy, enhanced (CBT-E); 14 focal psychodynamic therapy (FPT); 16 with good, 12 with poor outcome after 1 year]. Relations between the level of RF, type of treatment, and outcome were investigated using mixed linear models. Additionally, associations with depressive symptoms, weight gain, and therapeutic alliance were explored.ResultsMean in-session RF was low. It was higher in FPT when compared to CBT-E treatments. The findings point to an association between RF increase and a positive outcome. An increase in BMI in the first half of treatment was associated with higher subsequent in-session RF. There was no association between RF and depressive symptoms or the therapeutic alliance.DiscussionPatients with AN show a low capacity to mentalize in sessions, which seems to be at least partly dependent on the degree of starvation. The results suggest a possible relationship between an increase in in-session RF and outcome, which has to be replicated by further studies.

Starvation and relubrication mechanisms in grease lubricated oscillating bearings

Oscillating rolling element bearings can be found in various industrial applications. A popular example are the rotor blade bearings of wind turbines, which allow the rotor blades to turn around their longitudinal axis. These bearings are predominantly grease lubricated and expected to be running in a state of low velocity starvation. Elastohydrodynamic Lubrication (EHL) films in starved contacts are susceptible to the conditions of inlet lubricant supply. If the bearings are running under moderate starvation no early failure due to wear is expected. If the inlet conditions increasingly lead to a drying out of the contact, resulting in a heavily starved contact, metal-to-metal contact can lead to false brinelling and subsequent bearing failure. Using two different greases bearing experiments are used to gain an understanding of the mechanism of wear initiation. It is found that starvation seems to be a major contribution to wear appearing in the investigated operating conditions (2°-45° osc. angle, 0,2–5 Hz osc. frequency). The degree of starvation in the contact depends on the balance between lubricant displacement by the rolling element and the replenishment of lubricant during operation. The following conclusions could be drawn: Replenishment is highly dependent on the operating conditions such as the oscillation frequency, the oscillation amplitude, and lubricant rheology. For small oscillation angles the ability of the grease to release base oil with high mobility into the contact seams to be essential. For greater oscillation angles, after crossing a limiting angle, a secondary replenishment mechanism seems to become active. This prevents early wear initiation. At critical operating parameters, which mainly include high oscillation frequencies and medium oscillation angles, severe wear is initiated after just a few hundred oscillation cycles. By modifying an existing starvation factor the influences could be visualised and compared to the experimental results.

Growth, survivorship, and predator avoidance capability of larval shortnose sturgeon (Acipenser brevirostrum) in response to delayed feeding.

Larval shortnose sturgeon, reared at 17°C, were subjected to delayed feeding treatments of 0, 5, 10, 15, 18, and 23 days post-yolk absorption to examine effects of food deprivation on growth, survival, swimming activity, and escape capabilities. Starvation affected growth and survival but despite degree of starvation, larvae were able to resume growth and experience high survivorship following feeding. Specific growth rate based on larval dry weight for the period directly following first feeding was highest for the day 15 and 18 delayed feeding treatments. There were no differences in survival between the 0 and 5 day treatments, however survival was reduced to 71.2%, 45.4%, and 28.8% for 10, 15, and 18 day delayed feeding treatments, respectively. Shortnose sturgeon had a point-of-no-return (PNR; 55.7% initiated feeding) at ~19 days (or 42 days post-fertilization) following the full absorption of yolk. Mean percent swimming activity and swimming speeds showed an interaction between delayed feeding treatment and larval age, such that no differences were detected at 1 and 6 days post-yolk absorption, while these swimming behaviors generally increased or spiked as feeding was delayed for 10, 15, and 18 days post-yolk absorption. At 23 days post-yolk absorption, only swimming speed increased for larvae that were denied food for 18 days. While there was an interaction between delayed feeding treatments and age for proportion of larvae exhibiting an escape response, generally, larvae from all feeding treatments exhibited a positive escape response. There were also interactions between delayed feeding treatments and age post-yolk absorption for mean and maximum escape speeds, such that less aggressive escape responses were typically detected the longer larvae were denied food. Our research suggests that larval shortnose sturgeon increase physical activity during periods of starvation to find a food patch while remaining vigilant but maybe not as capable to defend against a predatory attack as fed individuals.

Tribo-Dynamics of Nanocomposite Grease Lubricated Point Contact Under Elastohydrodynamics Lubrication Regime

Friction is usually induced when the contacts are in relative motion, leading to mechanical vibration and consequently heat generation. The reduction of these undesirable parameters is possible by the application of greases, which intends to increase the service life of the bearings. The present work incorporates the frictional and vibration behaviors of concentrated point contact lubricated with bare and nanocomposite greases. The nanocomposite greases were formulated by dispersing different categories of nano-additives like reduced graphene oxide (rGO), calcium carbonate (CaCO3), and alumina (α-Al2O3) in bare grease (BG). The formulated nanocomposite greases are tested for film formation, frictional and vibrational response under a limited supply of greases. The use of transparent glass disk better analyses the profile of film thickness to understand the lubrication mechanism of the point contact. The microstructure of nano-additives and the formulated nanocomposite greases were characterized using high-resolution transmission electron microscopy (HRTEM). The presence of different functional groups in nano-additives and the formulated nanocomposite greases were characterized using Raman spectroscopy. The tribological contact operates under 3% and 30% slide-roll-ratio (SRR) for varying rolling speed (0.001–1 m/s) at a load of 30 N (Hertzian pressure, pH = 0.9 GPa). Film thickness, friction and vibration behavior were recorded to focus the tribo-performance, degree of starvation and dynamics of the tribological contact with slip varying from 3% to 30% SRR. The vibration level was refined to 32% with the addition of rGO nanosheets in BG. The incompatibility of α-Al2O3 with the grease structure results in disruption of tribo-dynamics behavior of the point contact.

Chaperone-E3 Ligase Complex HSP70-CHIP Mediates Ubiquitination of Ribosomal Protein S3.

In addition to its role in ribosome biogenesis, ribosomal protein S3 (RPS3), a component of the 40S ribosomal subunit, has been suggested to possess several extraribosomal functions, including an apoptotic function. In this study, we demonstrated that in the mouse brain, the protein levels of RPS3 were altered by the degree of nutritional starvation and correlated with neuronal apoptosis. After endurable short-term starvation, the apoptotic function of RPS3 was suppressed by Akt activation and Akt-mediated T70 phosphorylation, whereas after prolonged starvation, the protein levels of RPS3 notably increased, and abundant neuronal death occurred. These events coincided with ubiquitination and subsequent degradation of RPS3, controlled by HSP70 and the cochaperone E3 ligase: carboxy terminus of heat shock protein 70-interacting protein (CHIP). Thus, our study points to an extraribosomal role of RPS3 in balancing neuronal survival or death depending on the degree of starvation through CHIP-mediated polyubiquitination and degradation.

Starved Elastohydrodynamic Lubrication With Reflow in Elliptical Contacts

Under repeated overrollings, the elastohydrodynamic lubrication (EHL) film thickness can be much less than the fully flooded value due to the ejection of the lubricant from the track. The ejection of the lubricant is caused by the pressure flow in the inlet, and under conditions of negligible reflow, the reduction rate is predicted by the numerical analysis with a uniform inlet film thickness. However, the degree of starvation is determined by the balance of the ejection and reflow. In the previous papers for circular contacts, the reflow is taken into account using a nonuniform inlet film thickness obtained based on the Coyne–Elrod boundary condition. In this paper, the model for circular contacts is extended to elliptical contacts, which are of more practical importance in rolling bearings. The model is verified for the inlet distance and the film thickness using a roller on disk optical test device. Numerical results are fitted to an inlet distance formula, which is a function of the initial film thickness, the fully flooded central film thickness, the capillary number, and the ellipticity ratio. The inlet distance formula can be applied to the Hamrock–Dowson formulas for the starved film thickness.

Film Forming Behavior of Greases Under Starved and Fully Flooded EHL Conditions

ABSTRACTImproving knowledge on the film forming behavior of greases is essential to be able to develop efficient greases. This article examines how operating conditions (e.g., temperature, lubrication condition [fully flooded/starved]) and base oil viscosity influence the film forming properties of greases by comparing the behavior of two lithium-based greases and their respective base oils in rolling point contact. It is found that the onset and degree of starvation is controlled by speed (u) × viscosity (ν)/load (W) factor (uν/W) and temperature and that low uν/W values promote entrainment of thickener into contact. Thus, grease with low base oil viscosity shows significant thickener entrainment in the low speed region compared to the one with high base oil viscosity, which leads to the formation of thickener-rich viscous material during extended running with the low base oil viscosity grease. The results suggest that the shape of the film thickness versus speed curve is viscosity and uν/W range dependent. Furthermore, for the test conditions used in this study, grease-lubricated contacts appear to shift from the initial fully flooded condition to starved condition over a prolonged running of 2 h. The results from this study concur with those reported in the literature that fully flooded oil elastohydrodynamic lubrication (EHL) theory or film thickness cannot be directly applied or taken as a guideline in grease-lubricated contacts.

Mechanism for Controlling Oil Replenishment in Starved Elliptical EHL Contacts

Under rolling/sliding conditions of concentrated contacts, lubricant is pushed aside by the rolling element, leading to a depleted track and oil starvation. This study represents an attempt to investigate the effect of controlling oil replenishment within starved elliptical EHL contacts. The controlling of replenishment has been carried out by means of lubricant channeling via external slider with central slot to scrap the displaced lubricant on one of the contacting surfaces. The experiments were carried out for base oils with different viscosities using a spherical roller-on-disk configuration. The performance of lubricant flow control was assessed by measuring the film thickness and friction in the lubricated contact. The results show that the reconditioning of lubricant flow is a helpful method to prevent the occurrence of oil starvation and to improve the tribological performance of elliptical EHL contacts. However, the channeling of lubricant flow to modify the inlet supply of the Hertzian contact depends on operating conditions, the degree of starvation and oil viscosity.

On the prediction of steady-state wear rate in spur gears

Determination of wear rate in spur gears requires treatment of the mixed elastohydrodynamic lubrication problem along the gear's line of action (LoA). For this purpose, a procedure is developed to predict the film thickness, traction coefficient and the wear rate with provision for the interactions between the surface asperities of the gear's teeth at each point on LoA. The results reveal that the surface finish has a more pronounced influence on the wear rate compared to the traction coefficient. The wear results are also compared to those obtained by an engineering approach that utilizes an estimate of the contact flash temperature with reasonable accuracy. Also investigated is the effect of starvation on the wear rate for applications where the inlet is not fully flooded. The results show that wear rate can be enormously large depending on the degree of starvation.

A multi-pronged investigation into the effect of glucose starvation and culture duration on fed-batch CHO cell culture.

In this study, omics-based analysis tools were used to explore the effect of glucose starvation and culture duration on monoclonal antibody (mAb) production in fed-batch CHO cell culture to gain better insight into how these parameters can be controlled to ensure optimal mAb productivity and quality. Titer and N-glycosylation of mAbs, as well as proteomic signature and metabolic status of the production cells in the culture were assessed. We found that the impact of glucose starvation on the titer and N-glycosylation of mAbs was dependent on the degree of starvation during early stationary phase of the fed-batch culture. Higher degree of glucose starvation reduced intracellular concentrations of UDP-GlcNAc and UDP-GalNAc, but increased the levels of UDP-Glc and UDP-Gal. Increased GlcNAc and Gal occupancy correlated well with increased degree of glucose starvation, which can be attributed to the interplay between the dilution effect associated with change in specific productivity of mAbs and the changed nucleotide sugar metabolism. Herein, we also show and discuss that increased cell culture duration negatively affect the maturation of glycans. In addition, comparative proteomics analysis of cells was conducted to observe differences in protein abundance between early growth and early stationary phases. Generally higher expression of proteins involved in regulating cellular metabolism, extracellular matrix, apoptosis, protein secretion and glycosylation was found in early stationary phase. These analyses offered a systematic view of the intrinsic properties of these cells and allowed us to explore the root causes correlating culture duration with variations in the productivity and glycosylation quality of monoclonal antibodies produced with CHO cells.

A study on the effect of starvation in mixed elastohydrodynamic lubrication

The effect of starvation in mixed elastohydrodynamic lubrication (EHL) regime is studied. Numerical simulations are conducted for both line and point (elliptical) contacts with the consideration of the surface roughness. The degree of starvation is linked directly to the reduction in the lubricant mass flow rate. Results are presented to gain insight on the influence of starvation on the film thickness as well as the interaction between the surface asperities. Extensive sets of simulation results are used to quantify the effect of starvation in the EHL of rough surfaces. Expressions are developed to predict the percentage of the load carried by the surface asperities (asperity load ratio) as well as the reduction of the central and minimum film thickness in the starved mixed EHL.

Evaluation of Occurrence of Surface Brightness Irregularity in Cold Rolling of Stainless Steel with Emulsion

The manufacturing of stainless steel with higher brightness is improved using emulsion oil. However, in cold rolling of stainless steel with emulsion oil, it is well known that the surface brightness irregularity on the sheet surface after rolling occurs when the rolling speed is higher. It is estimated from the experimental results that the cause of the surface brightness irregularity is due to the degree of starvation in the emulsion rolling. The rolling experiments of the stainless steel with oil-in-water emulsion were carried out at various rolling speeds. The inlet oil film thickness was estimated using the evaluating system. In cold sheet rolling of stainless steel with emulsion oil, the surface brightness irregularity occurred at a rolling speed of 0.6 m/s with emulsion concentrations of 3, 5, and 10%. The experimental results showed that the surface brightness irregularity at cold coil rolling with emulsion of stainless steel occurred under a degree of starvation value of 0.16.

Nonpreemptive priority scheme for the S-MAC protocol in multimedia mobile sensor networks

S-MAC is a well-known medium access control (MAC) protocol designed for wireless sensor networks (WSNs). S-MAC uses a few novel techniques to reduce energy consumption and support self-configuration. Besides, S-MAC also achieves good scalability and collision avoidance by utilizing a combined scheduling and contention scheme. However, S-MAC does not have any priority scheme, making it unsuitable for multimedia applications and suffering from varying degree of starvation and fairness problems. In this paper, we propose a simple, efficient, but yet well-performing sliding contention window control mechanism to modify the S-MAC protocol such that priority can be supported along with the multimedia applications in multimedia mobile sensor networks. Furthermore, the proposed scheme could solve the starvation problem and alleviate the fairness problem. An analytic model is carried out to study the saturation throughput of proposed scheme. In addition, simulations were also conducted to analyze the proposed scheme and the results show that the proposed scheme is able to carry the prioritized traffic and mitigate the starvation and fairness problems.

Static Characteristics of Journal Bearings under Starved Lubricating Conditions

The static characteristics of journal bearings with an axial groove under starved lubrication are studied theoretically and a lubrication condition map is newly proposed. This map is represented using the contour map of the eccentricity ratio with the Sommerfeld number S in the horizontal axis and the dimensionless oil flow rate Qsup externally supplied in the vertical axis for the wide range of the operating conditions. It is found from the map that the eccentricity ratio increases with the decrease of Qsup. This tendency is more marked for a higher Sommerfeld number. Journal center loci show that the attitude angle decreases with Qsup. The degree of the starvation Λ and the oil supply rate Ψ are defined as the ratio of the dimensionless oil flow rate into the inlet of the oil film region to that obtained under the flooded lubrication condition and as the ratio of Qsup to Qsup* obtained under flooded lubrication conditions, respectively. The degree of starvation Λ varies with Ψ and the value of Λ can be determined by setting the value of Ψ. These facts suggest that the static characteristics and Λ are theoretically predicted once the value of Qsup or Ψ is determined.

An Architecture for Network Congestion Control and Charging of Non-cooperative Traffic

This paper proposes an architecture capable of reducing network congestion caused by the intense use of non-cooperative traffic. A charging scheme is imposed to all traffic that is carried over the UDP protocol (non-cooperative) given its intrinsic priority over TCP. Prices are calculated according to the degree of starvation undergone by cooperative TCP flows. When TCP flows experience a low performance, charges are high for non-cooperative flows and so the architecture tends to block new incoming UDP traffic. Knowledge about flows status is obtained through the use of flow protocol technology. Resources are reserved using firewall rules and custom-queueing mechanisms. An implementation of the architecture is made and tests show the effectiveness of our proposal in a real network scenario.

Famine and Death in Occupied Greece, 1941–1944 (review)

Reviewed by: Famine and Death in Occupied Greece, 1941–1944 Polymeris Voglis Violetta Hionidou, Famine and Death in Occupied Greece, 1941–1944. Cambridge: Cambridge University Press. 2006. Pp. xxvii + 261. 14 b/w plates. $99.00. The famine in Greece during the Second World War was, together with the one in Holland, the most lethal in the occupied Europe. When Greece capitulated in April 1941, the first signs of food scarcity appeared already in the summer of the same year. Flour, vegetables, and olive oil either disappeared from the market or their prices soared on the black market. As the collaborationist government was incompetent and the occupation authorities were unwilling to supply the starving population with food, a deadly famine broke out. In the winter of 1941–1942 thousands of people died of starvation or hunger-related diseases, literally in the streets of cities, especially Athens and Piraeus. Due to the humanitarian disaster, the Allies were obliged to lift the naval blockade and reached an agreement with the Germans allowing thousands of tons of wheat and other foodstuffs to be transported to Greece every month and distributed to the population under the auspices of the International Red Cross. There was no such degree of starvation in the subsequent years of the Nazi occupation, although scarcity of food continued to occur in different places and at different times due to shortcomings in the distribution of the relief and German retaliatory campaigns. Violetta Hionidou’s monograph is about the famine in occupied Greece and is the first book-length study on the subject. In it, she examines the causes of the famine in the cities and the countryside and then focuses on three islands—Mykonos, Syros, and Chios, discussing in more detail the impact on the local populations. She consulted the International Red Cross Archives and Italian and British archives to draw a general picture of the famine in Greece, while her findings for the three islands are based on material from the local archives, local newspapers, and interviews. The author divides the occupation into three periods to examine the changing characteristics of the famine: May 1941 to March 1942, April 1942 to April 1943, and May 1943 to the end of the occupation. The most severe famine occurred during the first period when the urban centers of Athens, Piraeus, and Thessaloniki were severely affected. Workers and artisans were the groups that suffered the most. In the second period, mortality levels were reduced thanks to the relief efforts, but the food crisis continued, albeit in different forms. In Athens and Piraeus high inflation and rising food prices put pressure on the poor and middle classes whereas in other parts of Greece high mortality occurred for different reasons. For instance, in Thessaloniki there was a malaria epidemic. In the third period, the food crisis was not as severe, but the population suffered from the combination of galloping inflation, German retaliation, and the curtailment of relief activities. The famine brought both death and other miseries. Hionidou repeatedly hints at the broader social and political consequences of the food crisis, but does not shed light on the radical changes that occurred in wartime Greece. After this general examination of the famine and the food situation in occupied Greece, Hionidou proceeds to examine the causes of the famine. She avoids any single-factor analysis and instead discusses many causes, assessing the [End Page 499] role that each played in the famine. First, the ineptitude of the Greek government and the conflict over decision-making between the Greek administration and occupation authorities created administrative chaos. It should be pointed out, however, that it was the primary responsibility of the occupation forces to provide food to the population and that they failed to do so. Second, plundering by soldiers, rather than the requisition of foodstuffs by the occupation forces, seems to have played a role in the famine since it drove the peasants to hoard their produce. This leads Hionidou to consider another factor that for a long time was believed to be prominent in the outbreak of the famine—the decline in agricultural production. She argues, as Yiorgos Margaritis has suggested, that agricultural production did not decrease...

Film Thickness Modulations in Starved Elastohydrodynamically Lubricated Contacts Induced by Time-Varying Lubricant Supply

Many elastohydrodynamically lubricated contacts in practical applications, e.g., in bearings, operate in the starved lubrication regime. As a result their performance is sensitive to variations of the lubricant layers present on the surfaces, which form the supply to the contact. Their shape is often determined by previous overrollings of the track and also by replenishment mechanisms and various migration effects. Variations of the layers induced in the direction of rolling lead to a time-varying lubricant supply to the contact. In this paper, by means of numerical simulations using a starved lubrication model, the film thickness modulations in the center of the contact induced by a harmonically varying inlet supply have been investigated. First, for a given load condition and layer wavelength, the effect of the nominal layer thickness (degree of starvation) and the layer variation amplitude is illustrated. Subsequently, using results for different load conditions, wavelengths, and degrees of starvation, it is shown that the response of the contact to such variations is determined by a nondimensional parameter, which represents the ratio of the entrainment length of the contact to the wavelength of the induced variation, and by the degree of starvation. A simple formula is presented for use in engineering predicting the ratio of the amplitude of the film modulations in the center of the contact to the amplitude of the layer variations in the inlet.

Refugia Preferences by the Spiders <I>Loxosceles reclusa</I> and <I>Loxosceles laeta</I> (Araneae: Sicariidae)

A variety of refugia were offered to different instars of brown recluse spiders, Loxosceles reclusa Gertsch and Mulaik, and a South American recluse spider, L. laeta (Nicolet), to determine whether they preferred certain types of refugia spaces. Variables included (1) crevice widths ranging from 3.2 to 21 mm, (2) horizontal and vertical orientations, and (3) new refugia or refugia that had silk deposited by a previous conspecific resident. An additional 30-d assay with similar-sized refugia studied each species' propensity for site fidelity or movement among refugia. L. reclusa preferred crevice widths > or = 9 mm with no correlation of body size to crevice width, whereas L. laeta preferred crevice sizes > or = 6.4 mm with a marginally significant correlation between crevice width and body size. Both species preferred (1) vertical instead of horizontal-oriented refugia and (2) refugia with conspecific silk compared with previously uninhabited refugia. There was no significant difference between the species in their propensity to move among refugia in the 30-d trial; however, both species had individuals that were always found in the same refugium for the entire assay and individuals changing refugia every 2-3 d. The propensity to switch refugia was not affected by the degree of starvation for the period tested as was initially hypothesized. The possible implications of this research toward developing novel control measures for Loxosceles spiders are discussed.

IMPACT OF EXPERIMENTAL DESIGN ON DROSOPHILA SEXUAL ISOLATION STUDIES: DIRECT EFFECTS AND COMPARISON TO FIELD HYBRIDIZATION DATA

Many studies of speciation rely critically on estimates of sexual isolation obtained in the laboratory. Here we examine the sensitivity of sexual isolation to alterations in experimental design and mating environment in two sister species of Drosophila, D. santomea and D. yakuba. We use a newly devised measure of mating frequencies that is able to disentangle sexual isolation from species differences in mating propensity. Variation in fly density, presence or absence of a quasi-natural environment, degree of starvation, and relative frequency of species had little or no effect on sexual isolation, but one factor did have a significant effect: the possibility of choice. Designs that allowed flies to choose between conspecific and heterospecific mates showed significantly more sexual isolation than other designs that did not allow choice. These experiments suggest that sexual isolation between these species (whose ranges overlap on the island of São Tomé) is due largely to discrimination against D. yakuba males by D. santomea females. This suggestion was confirmed by direct observations of mating behavior. Drosophila santomea males also court D. yakuba females less ardently than conspecific females, whereas neither males nor females of D. yakuba show strong mate discrimination. Thus, sexual isolation appears to be a result of evolutionary changes in the derived island endemic D. santomea. Surprisingly, as reported in a companion paper (Llopart et al. 2005), the genotypes of hybrids found in nature do not accord with expectations from these laboratory studies: all F1 hybrids in nature come from matings between D. santomea females and D. yakuba males, matings that occur only rarely in the laboratory.