Population dynamics of resource limited plants and their pollinators

In this paper we build upon and generalize an earlier model of the interactions between a plant and its pollinator (Ingvarsson and Lundberg, 1995). In this model we assume that the performance of the pollinator population is directly linked to the size of the plant population. To avoid the problem of both populations growing exponentially we have, without loss of generality, assumed the plant population to be resource limited. Analysis of the system shows that there exists either two or no internal equilibrium points. The case with no equilibrium points corresponds to the trivial case where the system cannot persist, resulting in the extinction of both the plant and pollinator population. When the two internal equilibrium points do exist, one of them will always be unstable. This unstable equilibrium can be viewed as an equivalent of the threshold criteria derived in Ingvarsson and Lundberg (1995) in the sense that whenever the system is initiated above the unstable equilibrium point, persistence of the system is assured, while both species will go extinct whenever the system is initiated below the unstable equilibrium point. The analytical results were verified by numerical simulations of the system. We conclude that the existence of a threshold criteria, below which the system cannot persist is a general feature of plant-pollinator systems. We discuss how the existence of the threshold criteria will affect the persistence of plant-pollinator systems in light of, for instance, habitat fragmentation or stochastic reductions in the densities of either the plant or pollinator population. We further highlight some recent empirical studies that indicate the existence of a threshold in natural populations below which extinction is inevitable.

Hormonal treatment before radical prostatectomy: a 3-year followup

PURPOSE

Hormonal treatment administered before radical prostatectomy has been shown to decrease the rate of positive surgical margins. We determine whether preoperative hormonal treatment has any impact on the subsequent failure rate.

MATERIALS AND METHODS

We prospectively evaluated 122 patients with stages T1bNxM0 to T3aNxM0, grades 1 to 3 prostate cancer, including 64 randomly assigned to immediate radical retropubic prostatectomy and 58 randomly assigned to radical retropubic prostatectomy preceded by 3 months of pretreatment with a gonadotropin-releasing hormone agonist. We performed intention to treat analysis on the data with failure defined as lymph node involvement, serum prostate specific antigen greater than 0.5 ng./ml., or the need for postoperative hormonal or radiation adjuvant treatment.

RESULTS

The positive margin rate was 23.6 versus 45.5% in the pretreatment plus prostatectomy versus prostatectomy only groups (p = 0.016). There were 20 failures (34.5%) in the pretreatment plus prostatectomy subgroup and 26 (40.6%) in the prostatectomy only group (p = 0.48). A negative surgical margin was associated with a significantly lower risk of progression than a positive surgical margin (20.8 versus 50.0%, p = 0.0016), and progression was delayed by approximately 1 year after hormonal pretreatment. However, at a median followup of 38 months there was no difference in progression-free survival (p = 0.57).

CONCLUSIONS

Although hormonal pretreatment significantly decreased the positive margin rate, it did not result in any difference in progression-free survival when followup exceeded 3 years. Thus, our current results do not support the routine administration of hormonal treatment before radical prostatectomy.

Hormonal treatment before radical prostatectomy: a 3-year followup

PURPOSE

Hormonal treatment administered before radical prostatectomy has been shown to decrease the rate of positive surgical margins. We determine whether preoperative hormonal treatment has any impact on the subsequent failure rate.

MATERIALS AND METHODS

We prospectively evaluated 122 patients with stages T1bNxM0 to T3aNxM0, grades 1 to 3 prostate cancer, including 64 randomly assigned to immediate radical retropubic prostatectomy and 58 randomly assigned to radical retropubic prostatectomy preceded by 3 months of pretreatment with a gonadotropin-releasing hormone agonist. We performed intention to treat analysis on the data with failure defined as lymph node involvement, serum prostate specific antigen greater than 0.5 ng./ml., or the need for postoperative hormonal or radiation adjuvant treatment.

RESULTS

The positive margin rate was 23.6 versus 45.5% in the pretreatment plus prostatectomy versus prostatectomy only groups (p = 0.016). There were 20 failures (34.5%) in the pretreatment plus prostatectomy subgroup and 26 (40.6%) in the prostatectomy only group (p = 0.48). A negative surgical margin was associated with a significantly lower risk of progression than a positive surgical margin (20.8 versus 50.0%, p = 0.0016), and progression was delayed by approximately 1 year after hormonal pretreatment. However, at a median followup of 38 months there was no difference in progression-free survival (p = 0.57).

CONCLUSIONS

Although hormonal pretreatment significantly decreased the positive margin rate, it did not result in any difference in progression-free survival when followup exceeded 3 years. Thus, our current results do not support the routine administration of hormonal treatment before radical prostatectomy.

Falloposcopy in conjunction with laparoscopy: possibilities and limitations

Falloposcopy is a transvaginal microendoscopic technique to explore the human Fallopian tube from the uterotubal ostium to the fimbrial end. Falloposcopy provides a unique possibility to visualize endotubal disease and may be used therapeutically for removal of debris and for cutting down filmy intraluminal adhesions. To assess the clinical performance of falloposcopy as part of an infertility investigation, a total of 43 women scheduled for laparoscopy as part of an investigation of infertility had a falloposcopy performed in conjunction with the laparoscopy. All women were investigated at Danderyd Hospital, Stockholm and Akademiska Hospital, Uppsala, during 1995 and 1996. Images from the endosalpinx were obtained in 26 of 43 women (60.5%). In 10 women (23.3%), it was possible to obtain images from both tubes. No images were of sufficient quality to describe the entire tubal mucosa in detail. Falloposcopy represents a unique tool for visualization of endotubal disease and may provide a valuable instrument for in-vivo exploration of tubal physiology. However, certain technical problems limit the usefulness of this method in routine clinical practice. These technical problems have to be solved before falloposcopy can achieve a central position in investigation and treatment of tubal disease.

Radionuclide hysterosalpingography is not predictive in the diagnosis of infertility

OBJECTIVE

To investigate whether radionuclide hysterosalpingography (radionuclide HSG), which has been suggested as a more functional approach to the diagnosis of tubal infertility than conventional patency tests, is predictive in the diagnosis of infertility.

DESIGN

A retrospective analysis of data from an inquiry form containing questions about pregnancy outcome after radionuclide HSG.

SETTING

University hospital-based, tertiary care infertility clinic.

PATIENT(S)

Two hundred sixteen women had an infertility work-up including radionuclide HSG performed between April 1986 and April 1993. Forty-one (18.9%) women were excluded from the study; 9 had moved to unknown addresses, 16 did not answer the inquiry, and 16 gave answers that were not interpretable. There were 175 (81.1%) women in the final study group.

INTERVENTION(S)

An inquiry form containing questions regarding pregnancy was sent to 207 women who undergone radionuclide HSG as a routine procedure in their infertility workup.

MAIN OUTCOME MEASURE(S)

Occurrence of pregnancy related to outcome of radionuclide HSG and its test properties calculated.

RESULT(S)

Bilateral or unilateral tubal transport was demonstrated by radionuclide HSG in 129 women, of whom 66 (51%) later became pregnant. Of the pregnant women, 36 (55%) had successful infertility treatment, whereas 30 (45%) reported spontaneous pregnancy. Forty-six women showed no transport at radionuclide HSG. Twenty-five (54%) of these women became pregnant, 14 (56%) with infertility treatment and 11 (44%) without infertility treatment. The predictive values of transport and no transport radionuclide HSG were 0.51 and 0.46, respectively. The sensitivity of radionuclide HSG was 0.25, and the sensitivity was 0.73. Likelihood ratios for pregnancy when radionuclide HSG showed transport and no transport were 1.03 and 0.93, respectively.

CONCLUSION(S)

Our data strongly indicate that a single radionuclide HSG investigation is not able to predict fertility potential.

Calcium-binding mechanism of human nonerythroid alpha-spectrin EF-structures

We have used circular dichroism and 1H- and 15N-NMR spectroscopy to investigate calcium binding to the two EF-hands of human nonerythroid or alphaII-spectrin. Comparison of the 1H-NMR spectra from the peptide containing both EF-hands to the peptides containing the single EF-I and EF-II structures showed that both the structural and calcium-binding properties are significantly different. Further studies of the 121 amino acid peptide containing both EF-hands using circular dichroism and NMR showed that the binding of calcium ions induces conformational changes. To investigate the calcium-binding mechanism, the chemical shifts changes were recorded using multidimensional NMR spectroscopy during calcium titration. A total of 25 titration curves were obtained, each corresponding to the chemical shift changes of individual amino acid residues. The shapes of these titration curves were either hyperbolic or sigmoidal. Using factor analysis, two functions were extracted, one hyperbolic and one sigmoidal, which accounted for nearly all information present in the titration curves. By fitting the two functions to binding curves based on different binding models, we found that the binding mechanism is best described as sequential. Since the sigmoidal type was more pronounced in the titration curves corresponding to residues from the first EF-hand, we suggest that calcium binding to the first EF-hand is described by the sigmoidal function, and that the hyperbolic function describes calcium binding to the second EF-hand. Therefore, is seems likely that the second EF-hand must contain bound calcium before the first EF-hand can bind.

Radionuclide hysterosalpingography does not distinguish between fertile women, before tubal sterilization, and infertile women

The female genital tract is capable of active transport that can be demonstrated by serial scintigraphic imaging over time (radionuclide hysterosalpingography; RN-HSG). RN-HSG has been suggested to offer a more functional approach to tubal infertility diagnosis than conventional patency tests. However, before RN-HSG can be recommended as a routine method, its reliability in showing active transport in fertile women must be demonstrated. Therefore we compared RN-HSG in two groups: 38 fertile women before tubal sterilization and 38 women undergoing infertility work-up. Tubal transport demonstrated by RN-HSG was comparably distributed in both groups and classified as bilateral (17 versus 19), unilateral (12 versus 7) or no transport (6 versus 9). In each group three RN-HSG images were not interpretable. There was no association between patency test results and RN-HSG in the two groups. Our data suggest that RN-HSG in its present form does not seem to be a reliable method for infertility work-up. Because RN-HSG and patency tests most probably measure different properties of the genital tract, the phenomenon of active particle transportation should be studied further to enable the development of a reliable tool for the investigation of tubal function.

The risk of malignancy in the surgical margin at radical prostatectomy reduced almost three-fold in patients given neo-adjuvant hormone treatment

OBJECTIVES

To investigate the outcome of neo-adjuvant hormone treatment before radical prostatectomy regarding local tumour extension, peri-operative blood loss and operation time.

PATIENTS

Of 111 surgically treated patients with prostate cancer (T1b-T3a, N0, M0, G1-3), 55 were randomised to immediate radical prostatectomy and 56 to 3 months of neo-adjuvant treatment with triptorelin (3.75 mg i.m. every 28 days) and cyproterone acetate (50 mg b.i.d. for 3 weeks to prevent flare).

RESULTS

No differences were found in blood loss or operation time but patients who had neo-adjuvant treatment had a significantly lower frequency of positive margins (41 vs. 23%, p = 0.013).

CONCLUSION

Neo-adjuvant treatment does not facilitate radical prostatectomy but may improve the chance of local cure. This must, however, be documented with long-term follow-up in randomised patients.

Cloning, expression and characterization of two putative calcium-binding sites in human non-erythroid alpha-spectrin

The C-terminus of alpha-spectrins contains two putative calcium-binding sites or EF-hands. To characterize the binding, we have isolated clones from a human fetal liver cDNA library and expressed several fragments comprising either one or both of these sites. When the isolated clones were sequenced, we found that three consecutive nucleotides differed compared to the published sequence. The discrepancy affected two codons in the first of the two putative calcium sites. These codons translated into glutamate and phenylalanine, which are identical to the residues present at the same position in other alpha-spectrins. In the presence of magnesium, only recombinant peptides comprising the second putative site bound calcium as determined by a calcium overlay assay. Although the first putative EF-hand appeared to bind some calcium in the absence of magnesium, no binding could be detected under stringent conditions. Therefore, it is likely that the second EF-hand constitutes the only functional calcium-binding site in the C-terminus of human non-erythroid alpha-spectrin. Since peptides comprising the second EF-hand bound calcium nearly as well as intact spectrin, it is also apparent that the second EF-hand constitutes the major binding site for calcium in spectrin. The relative change in negative ellipticity, induced by the binding of calcium, indicates a dissociation constant of approximately 120 microM.

Characterization of the binding of calmodulin to non-erythroid spectrin

Both brain and erythrocyte spectrin bound calmodulin in a calcium-dependent manner when immobilized on a polyvinylidene difluoride (PVDF) membrane, though the affinity of the non-erythroid spectrin was much greater than that of the erythroid isoform. The interaction was characterized further using equilibrium partition. In the presence of calcium, the partition behavior of calmodulin was affected by both spectrins, though brain spectrin caused a much larger change in partition. However, in both cases it was evident that the observed partition behavior of calmodulin was due to complex formation with spectrin. Analysis of the equilibrium partition data indicated the presence of a high-affinity site characterized by a dissociation constant of about 0.3 microM and probably one or more much weaker sites (> 0.3 mM). The presence of at least two distinct binding sites was substantiated by the observation that truncated recombinant spectrin fusion proteins comprising either the middle part or the C-terminal of non-erythroid alpha-spectrin bound calmodulin.

Adolescent fertility and the educational attainment of young women

Analyses based on a sample of 2,795 women interviewed annually from 1979 through 1991 in the National Longitudinal Survey of Youth show that early childbearing lowers the educational attainment of young women. After controls for an extensive set of personal and community characteristics are taken into account, having a child before age 20 significantly reduces schooling attained by almost three years among whites, blacks and Hispanics. Having a child before age 18 has a significant effect only among blacks, reducing years of schooling by 1.2 years.

Parent-offspring conflicts over reproductive efforts: variations upon a theme by Charnov

A novel formulation of the theory of parent-offspring conflict is proposed. The basis of this formulation is an application of traditional life-history theory in combination with simple genetic arguments. The advantage with this approach is conceptual, and the formulation is not in variance with earlier studies in the area. Parent-offspring conflict is, in our formulation, not seen as a conflict between individuals, but as a tradeoff--an age-specific selection pressure acting on a trait, which is favourable when an individual is offspring and disadvantageous when it becomes parent. Using an ESS approach we investigate a simple offspring-wins problem: we find that a gene causing assertiveness of offspring will increase when rare, because the advantage thus gained by an assertive individual when young exceeds the cost incurred as adult by that half of its own offspring which belongs to the same assertive genotype.

Health problems and self-medication among Swedish travellers

500 consecutive travellers seeking pre-travel health advice were issued a questionnaire before leaving Sweden to continuously record health problems and use of medication during travel. Of 442 subjects who turned in assessable questionnaires (232 male and 210 female, mean age 37 years), 81% travelled to areas at high risk for the acquisition of diarrhea. The mean duration of travel was 4 weeks. During travel 218 (49% at 95% CI 44.3 to 53.7%) of the travellers experienced some illness and 61 (14%) had symptoms of more than one illness. The mean duration of illness was 4.5 days, and 65 subjects (30% of ill travellers) were confined to bed for a mean duration of 2 days. The incidence of illness was significantly (p < 0.01) higher among travellers to high risk than to low risk areas (55% vs 26%), among young travellers than among elderly (65% vs 33%), and among those going on adventure tours compared with recreational tourists (74% vs 41%). Diarrhea was reported by 36% (95% CI 31.6 to 40.5%), and respiratory tract infection by 21% (95% CI 17.2 to 24.8%). Self-medication with one or several drugs was initiated by 163 (75%) travellers experiencing illness during travel. Thus, every second Swedish traveller to tropical and subtropical areas experienced some kind of travel-related, often incapacitating, health problem.

Modeling and simulating the evolution of resistance against antibiotics

An epidemiological model is proposed for the spread of resistance against antibiotics in populations of bacterial pathogens. The host population, which is assumed to be constant, is divided into three compartments, viz. susceptible, hosts infected by an antibiotic-sensitive strain and hosts infected by a resistant strain. It is further assumed that susceptibles can be infected by either strain and that there is a possibility for cross-infection between hosts infected by the two strains. The rate of cross-infection can be enhanced by mutations or the transfer of plasmids conferring resistance. Equilibrium analysis was performed in order to determine which of the strain 'wins' the competition by the host. It is assumed that the eventual shift in the competition between the two strains is due to treatment by antibiotic (selective pressure).

Developmental steps for radionuclide hysterosalpingography

The active oviductal transportation capacity was studied in 73 infertile women by the use of a new deposition technique of radioactive particles into the internal cervical os. The main reason for this study was that a previous observation had shown that such a transportation capacity was lacking in 41% of the infertile patients with a normal hysterosalpingogram. The examination was performed in the immediate preovulatory phase, i.e. on days -3 to 0 before the ovulation, as measured by the basal body temperature during two preceding cycles. The deposition of 99mTc-labelled albumin particles of 0.2-1.0 micron at the internal cervical os and the interpretation of the radionuclide images are described in detail. The results show that the bilateral active tubal transportation capacity was present in 42 patients. An impaired transportation capacity was diagnosed in 22 patients. In 9 patients, the particles never reached the uterine cavity, or all activity leaked back to the vagina.

Characterization of calcium binding to spectrins

Calcium binding to brain and erythrocyte spectrins was studied at physiological ionic strength by a calcium overlay assay and aqueous two-phase partitioning. When the spectrins were immobilized on nylon membranes by slot blotting, the overlay assay showed that even though both spectrins bound 45Ca2+, the brain protein displayed much greater affinity for calcium ions than erythrocyte spectrin did. Since the observed binding was weaker than that displayed by calmodulin under similar conditions, the overlay assay results indicated that the binding must be weaker than 1 microM. The phase partition experiments showed that there are at least two sites for calcium on brain spectrin and that calcium binding to one of these sites is reduced significantly by magnesium ions. From the partition isotherm, the dissociation constants were estimated as 50 microM for the Mg(2+)-independent site and 150 microM for the Mg(2+)-dependent site. The phase partition results also showed that erythrocyte spectrin bound calcium ions at least 1 order of magnitude weaker. By examining calcium binding to slot-blotted synthetic peptides, we identified two binding sites in brain spectrin. One mapped to the second putative calcium binding site (EF-hand) in alpha-spectrin and the other to the 36 amino acid residue long insert in domain 11. In addition, a tryptic fragment derived from the C-terminal of erythrocyte alpha-spectrin, which contained the two postulated EF-hands, also bound calcium. These findings suggest that the calcium signal system may also involve direct binding of calcium to spectrin beside known calcium modulators such as calmodulin and calpain.(ABSTRACT TRUNCATED AT 250 WORDS)

Evolution of increased susceptibility to infectious diseases in age structured populations

Current theory on the epidemiology of infectious diseases in genetically heterogeneous host populations ignores age structure. Thus, the possibility that microparasites might have negative effects on fitness in different ways during different phases of the lives of their hosts is not accounted for. For example, infections causing mortality and morbidity among juveniles might also have an impairing effect on reproduction among adults, as is the case in many so called childhood diseases. I demonstrate that when this is the case there may be a selective pressure for the host to evolve a higher level of susceptibility to an infection, provided it has the following properties: it should (i) provide life-long immunity, (ii) have a negative effect on reproduction and (iii) not cause too many mortalities.

Measurement of human cervical compliance

A critical evaluation of the various methods for the measurement of the compliance of the human cervix uteri was made. The resistance of this tissue to a dilating force was measured by a previously constructed strain gauge instrument equipped with exchangeable Pratt cervical dilators. The dilating resistance offered by the cervical canal was recorded on a polygraph at a constant paper speed. Control experiments in which the dilating instrument was allowed to meet artificial cellulose tissue showed that the peak value recorded was of importance for estimating cellulose tissue resistance. Measurements of the area under the curve were shown to be of minor importance in this system. Using this technique in clinical applications, it was also shown that peak resistance provides the most accurate measurement of human cervical resistance.

Gangrenous dermatitis caused by Corynebacterium ulcerans in Richardson ground squirrels

Gangrenous dermatitis caused by Corynebacterium ulcerans developed in 63 of 350 wild Richardson ground squirrels (Spermophilus richardsonii). Six squirrels died of toxemia and/or septicemia, but 57 responded to topical and parenteral administration of antibiotics. The epizo-otic was believed to be associated with fighting; infected and carrier ground squirrels most likely transmitted the C ulcerans through bite wounds. Individuals handling ground squirrels should be cautioned that C ulcerans may produce a diphtheria-like disease in human beings.

DNA flow cytometry and histopathological grading of paraffin-embedded prostate biopsy specimens in a survival study

Methods to disintegrate old paraffin-embedded tissue blocks for the application of DNA flow cytometry open up new possibilities for retrospective studies on the correlation between tumor cell nuclear DNA pattern and prognosis of the neoplastic disease. In the present work we used such a method to study the relationship between DNA ploidy, histopathological grade, and survival for 50 patients with prostate carcinomas diagnosed 1958-1974. Plugs of histologically identified tissue from benign and tumor areas were sampled from paraffin blocks of prostate biopsy specimens by using a 4-mm skin biopsy punch. Thirty-micron sections were cut from each plug for dewaxing and disintegration. The cell suspensions obtained were stained with 4',6-diamidino-2-phenylindole dihydrochloride and analyzed by flow cytometry. In about one-half of the cases where two or more plugs were analyzed we found a heterogeneous tumor cell nuclear DNA pattern. No apparent correlation was found between the histopathological grade and the DNA ploidy. Using Cox's multiple regression analysis, we found a significant correlation between DNA ploidy and survival of these patients (P = 0.043) when we controlled for histopathological grade (Dhom grade), acid phosphatase level, occurrence of metastases, age, year of diagnosis, and type of biopsy. The correlation between DNA ploidy and survival was just above the level of significance (P = 0.059) when Gleason grade was substituted for Dhom grade in the regression model.