The arsenic (As) drinking water crisis in south and south-east Asia has stimulated intense study of the microbial processes controlling the redox cycling of As in soil-water systems. Microbial oxidation of arsenite is a critical link in the global As cycle, and phylogenetically diverse arsenite-oxidizing microorganisms have been isolated from various aquatic and soil environments. However, despite progress characterizing the metabolism of As in various pure cultures, no functional gene approaches have been developed to determine the importance and distribution of arsenite-oxidizing genes in soil-water-sediment systems. Here we report for the first time the successful amplification of arsenite oxidase-like genes (aroA/asoA/aoxB) from a variety of soil-sediment and geothermal environments where arsenite is known to be oxidized. Prior to the current work, only 16 aroA/asoA/aoxB-like gene sequences were available in GenBank, most of these being putative assignments from homology searches of whole genomes. Although aroA/asoA/aoxB gene sequences are not highly conserved across disparate phyla, degenerate primers were used successfully to characterize over 160 diverse aroA-like sequences from 10 geographically isolated, arsenic-contaminated sites and from 13 arsenite-oxidizing organisms. The primer sets were also useful for confirming the expression of aroA-like genes in an arsenite-oxidizing organism and in geothermal environments where arsenite is oxidized to arsenate. The phylogenetic and ecological diversity of aroA-like sequences obtained from this study suggests that genes for aerobic arsenite oxidation are widely distributed in the bacterial domain, are widespread in soil-water systems containing As, and play a critical role in the biogeochemical cycling of As.

To determine the diagnostic accuracy of state, minimally invasive clinical and physical signs (or sets of signs) to be used as screening tests for detecting impending or current water-loss dehydration, or both, in older people by systematically reviewing studies that have measured a reference standard and at least one index test in people aged 65 years and over. 1 Clinical and physical signs for identification of impending and current water-loss dehydration in older people (Protocol)

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. The life cycles of a wide variety of organisms include a dispersal phase that precedes reproduction. The main function of this stage is to select an appropriate habitat for reproduction and the development of offspring. Several models of optimal habitat selection have assumed that the optimal behavior results in an "ideal free distribution," in which no individual could increase its fitness by being elsewhere (e.g., Fretwell and Lucas 1970;Fretwell 1972). In species whose dispersal stage is brief or marked by heavy mortality, however, the benefits of rejecting suboptimal habitats may be outweighed by the cost of failing to find a habitat at all. The University of Chicago Press andModels of time-limited habitat selection have been presented by Levins (1968), Levins and MacArthur (1969), Jaenike (1978), andCourtney (1982). Specificity (i.e., rejection of suboptimal habitats) is favored if optimal habitats are abundant, if a long time is available for the search, or if fitness in inferior habitats is low. A related model has been used to explain the high incidence of polyphagy among aphids inhabiting areas of high floral diversity, since this is associated with relatively low densities of each plant species (Dixon et al. 1987). Finally, Doyle (1979) has shown that in species with a constant instantaneous mortality rate during dispersal, an initial "exploratory phase" may be adaptive if the abundance of optimal sites is unpredictable.I consider here the evolution of habitat-acceptance behavior in a time-limited disperser. This behavior is expressed as the probability that a habitat of a particular type is accepted (i.e., that the dispersing organism settles, rather than searching further) once it has been encountered. The model includes the possibility that the probability of acceptance varies during the course of the dispersal phase. In addition, since the total time available is held constant, the expected future time available declines. (This is often more realistic than the frequent assumption of constant mortality in, e.g., nonfeeding dispersers.) These assumptions are similar to those on which Jaenike (1978) based his model, except that in his inequality (1) it is implicitly assumed that if a host plant (i.e., {habitat) of a particular type is rejected, no further hosts of this type will be encountered (or, if encountered, they

Summary. Background: Venous thromboembolism (VTE) is postulated as a complex disease, but the heritability and mode of inheritance are uncertain. Objective: To determine if VTE (i) segregates in families; (ii) is attributable to inheritance, shared environment, or both; and (iii) the possible mode of inheritance. Patients and methods: In a family-based study of relatives from 751 probands (60% female) with objectively diagnosed VTE (without cancer), we performed complex segregation analyses corrected for mode of ascertainment, considering agespecific, non-gender-and gender-specific liability classes under Mendelian and non-Mendelian assumptions. We tested 12 models categorized into four model sets: (i) sporadic (assumes no genetic effect); (ii) Mendelian inheritance of a major gene (including dominant, additive, recessive or codominant classes); (iii) mixed model (Mendelian inheritance including the same four classes plus the effect of polygenes); and (iv) nonMendelian. Results: Among the 16 650 relatives, 753 (48% female) were affected with VTE, of whom 62% were first-degree relatives. The sporadic model was rejected in both non-genderand gender-specific liability class analyses. Among the remaining gender-specific models, the unrestricted (non-Mendelian) inheritance model was favored with an estimated heritability of 0.52. Among the Mendelian models, the dominant mixed model was preferred, with an estimated heritability and major disease allele frequency of 0.62 and 0.25, respectively, suggesting an effect of several minor genes. Conclusion: A multifactorial non-Mendelian inheritance model was favored as the cause for VTE, while a model postulating a purely environmental cause was rejected. VTE is probably a result of multigenic action as well as environmental exposures.

Summary 0[ For a full assessment of explanations for the evolution of host!speci_city it is necessary to estimate the probability that a dispersing parasite _nds a host[ We develop a method of estimating this success rate from samples of dispersing parasites and populations resident on hosts[ 1[ Applying this method to data on the bird cherry!oat aphid\ Rhopalosiphum padi "L[#\ from southern Scotland in 0873Ð81\ we estimate that 9=5) of the autumn migrants _nd hosts[ 2[ With such a low success rate\ there should be selection for a broadening of host range\ to include any host on which the colonist|s _tness is more than about 9=5) of that on the normal hosts[ We argue that neither nutrition nor the need for {enemy! free space| are su.cient explanations of the host!speci_city of this animal\ and propose instead that it is the host|s role as a rendezvous for mating that constrains the migrants to their costly host!speci_city[ 3[ We also discuss the implications of this low success rate for the hypothesis that aphids speciate sympatrically through the formation of host races[ Key!words] host alternation\ migration\ overwintering\ Rhopalosiphum padi\ sympatric speciation[ Journal of Animal Ecology "0887# 56\ 652Ð662