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Methodological Constraints (methodological + constraint)
Selected AbstractsGenetic transduction in freshwater ecosystemsFRESHWATER BIOLOGY, Issue 6 2008OLADELE A. OGUNSEITAN Summary 1. Lateral genetic exchange is a profound consequence of the co-existence of viruses (bacteriophages) and bacteria in freshwater ecosystems. Transduction is distinct from other mechanisms of genetic exchange because it is driven by potentially lethal agents external to the donor and recipient cells. Therefore, transduction is reputed to be a major driving force behind the diversity in natural populations and communities of bacteria. 2. Both generalized transduction (where every segment of the donor's genome has equal chance of being transferred to a recipient cell) and specialized transduction (where certain donor gene sequences are transferred at higher frequencies than others based on their proximity to the integration site of the transducing bacteriophage genome) have been demonstrated for various freshwater bacteria. However, these genetic exchange events occur at frequencies that vary widely, from 10,2 to 10,10 transductants per recipient, depending on the influence of various physical, chemical and biotic environmental factors on the outcome of phage,host encounters. Methodological constraints limit the interpretation of results from early studies of transduction in freshwaters because those studies introduced exogenous organisms in microcosms and excluded, to different extents, naturally occurring environmental conditions and their variability. 3. To assist the design and extrapolation of empirical observations, mathematical models including application of Group Theory are useful to estimate boundaries of the impact of transduction in generating and maintaining microbial diversity in freshwater. These theoretical excursions generate hypotheses and questions that can only be answered through refinement of current empirical estimates of transduction frequency, polarity of gene mobilization, bacteriophage host ranges, and the influence of gradients in environmental parameters that characterize freshwater ecosystems. [source] I,Radical Scepticism, Epistemic Luck, and Epistemic ValueARISTOTELIAN SOCIETY SUPPLEMENTARY VOLUME, Issue 1 2008Duncan Pritchard It is argued that it is beneficial to view the debate regarding radical scepticism through the lens of epistemic value. In particular, it is claimed that we should regard radical scepticism as aiming to deprive us of an epistemic standing that is of special value to us, and that this methodological constraint on our dealings with radical scepticism potentially has important ramifications for how we assess the success of an anti-sceptical strategy. [source] Trends in precipitation on the wettest days of the year across the contiguous USAINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2004Patrick J. Michaels Abstract Over the course of the 20th century, average annual precipitation for the contiguous USA has increased by nearly 10%. This increase has been described as being dominated by ,disproportionate' increases in extreme precipitation events. However, methodological constraints have confounded detailed interpretation of such results. Here, we briefly describe those limitations and re-evaluate the nature of the observed precipitation changes using a method that allows for a more accurate examination of changes in the proportion of precipitation delivered in extreme daily events. We focus our analysis only on the trends in precipitation on the 10 wettest days of the year and compare the trends observed on those days with the trend in overall precipitation. When averaged across the USA, we find that the precipitation trends on the 10 wettest days of the year are not significantly different from the trend in total overall precipitation. On a regional level, in the northeast and southeast there is some evidence that the rate of precipitation increase on the wettest days exceeds that of total precipitation, whereas in the rest of the country the precipitation on the wettest days is increasing at a rate less than the increase in total precipitation. Copyright © 2004 Royal Meteorological Society [source] Population differences in the testosterone levels of young men are associated with prostate cancer disparities in older menAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 4 2010Louis Calistro Alvarado Although there is evidence that greater exposure to testosterone is associated with an increased risk of prostate cancer, a recent analysis of 18 prospective studies found no relationship between levels of endogenous sex hormones and prostate cancer development. However, the reviewed studies were subject to methodological constraints that would obscure any potential relationship between prostate cancer and androgenic hormones. If prostate cancer risk is mediated by lifetime exposure to testosterone, then case-control studies that concentrate on endogenous sex hormones near the ages that prostate cancer is diagnosed would provide limited information on cumulative testosterone exposure across the lifespan. Alternately, early adulthood has been suggested as the most salient period to evaluate the influence of steroid physiology on prostate carcinogenesis. As such, an exhaustive literature search was completed to obtain testosterone values reported for study samples of younger men, along with prostate cancer incidences for the larger populations from which the study populations were sampled. A novel analytical method was developed to standardize, organize, and examine 12 studies reporting testosterone levels for 28 population samples. Study populations were generally apportioned according to ethnicity and geographic residence: Americans of African, Asian, Caucasian, and Hispanic ancestry from several different regions within the United States as well as men from China, Germany, Japan, Kuwait, New Zealand, South Korea, and Sweden. Population differences in the testosterone levels of young men were significantly associated with population disparities in the prostate cancer incidence of older men (Spearman's rho = 0.634, p = 0.002). Am. J. Hum. Biol. 2010. © 2010 Wiley-Liss, Inc. [source] The Clitoral Photoplethysmograph: A New Way of Assessing Genital Arousal in WomenTHE JOURNAL OF SEXUAL MEDICINE, Issue 6 2009Jeroen Gerritsen MSc ABSTRACT Introduction., In the present study, we introduce clitoral photoplethysmography as an instrument to assess clitoral blood volume (CBV). In research on female sexual functioning, vaginal pulse amplitude (VPA), as measured using vaginal photoplethysmography, has been used extensively as a measure of vaginal vasocongestion. Measurement of clitoral blood flow has thus far been problematic, mainly because of methodological constraints. Aim., To demonstrate that CBV is a valuable, easy to use complementary measure for the female sexual response, offering additional information to the VPA. Methods., Thirty women with and without female sexual dysfunction (FSD) watched neutral and erotic film clips. At the end of the erotic clip, the session was interrupted to induce inhibition of the sexual response. Another neutral clip followed the interruption. VPA and CBV were measured simultaneously, as well as skin conductance levels (SCLs), to assess the amount of sympathetic activity. Main Outcome Measures., VPA, CBV, SCL. Results., For both FSD and non-FSD women, VPA and CBV increased when sexually explicit material was presented. Changes in skin conductance significantly predicted changes in CBV (b = ,0.61, t[27] = ,3.88, P < 0.001), but not in VPA. A large increase in sympathetic activity was accompanied by a large decrease in CBV. Furthermore, a large increase in CBV at the end of the erotic film clip presentation, as compared with the neutral clip, was accompanied by a relatively small increase in VPA (b = ,0.39, t[29] = ,2.25, P < 0.033). Conclusion., CBV is a valid and sensitive tool to measure the female genital response. In the present study, it was particularly useful in investigating sexual inhibition, when used in combination with SCL. Furthermore, high CBV appeared to inhibit VPA, suggesting that VPA reflects an automatic preparatory response rather than genital arousal per se. Gerritsen J, van der Made F, Bloemers J, van Ham D, Kleiverda G, Everaerd W, Olivier B, Levin R, and Tuiten A. The clitoral photoplethysmograph: A new way of assessing genital arousal in women. J Sex Med 2009;6:1678,1687. [source] Sexual selection research on spiders: progress and biasesBIOLOGICAL REVIEWS, Issue 3 2005Bernhard A. Huber ABSTRACT The renaissance of interest in sexual selection during the last decades has fuelled an extraordinary increase of scientific papers on the subject in spiders. Research has focused both on the process of sexual selection itself, for example on the signals and various modalities involved, and on the patterns, that is the outcome of mate choice and competition depending on certain parameters. Sexual selection has most clearly been demonstrated in cases involving visual and acoustical signals but most spiders are myopic and mute, relying rather on vibrations, chemical and tactile stimuli. This review argues that research has been biased towards modalities that are relatively easily accessible to the human observer. Circumstantial and comparative evidence indicates that sexual selection working via substrate-borne vibrations and tactile as well as chemical stimuli may be common and widespread in spiders. Pattern-oriented research has focused on several phenomena for which spiders offer excellent model objects, like sexual size dimorphism, nuptial feeding, sexual cannibalism, and sperm competition. The accumulating evidence argues for a highly complex set of explanations for seemingly uniform patterns like size dimorphism and sexual cannibalism. Sexual selection appears involved as well as natural selection and mechanisms that are adaptive in other contexts only. Sperm competition has resulted in a plethora of morphological and behavioural adaptations, and simplistic models like those linking reproductive morphology with behaviour and sperm priority patterns in a straightforward way are being replaced by complex models involving an array of parameters. Male mating costs are increasingly being documented in spiders, and sexual selection by male mate choice is discussed as a potential result. Research on sexual selection in spiders has come a long way since Darwin, whose spider examples are reanalysed in the context of contemporary knowledge, but the same biases and methodological constraints have persisted almost unchanged through the current boom of research. [source] | ||||||||||