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Distribution by Scientific Domains


Selected Abstracts


Co-evolution between ectoparasites and their insect hosts: a simulation study of a damselfly,water mite interaction

ECOLOGICAL ENTOMOLOGY, Issue 6 2001
Jens Rolff
Summary 1. A simulation model investigating the co-evolution of water mites infesting their aquatic insect hosts during emergence is presented. The model is based on field and experimental studies of the ectoparasitic water mite Arrenurus cuspidator and the damselfly Coenagrion puella. 2. Three scenarios were studied: (1) Only the host was allowed to evolve timing of emergence, while the timing of the parasites' infestation opportunity was held constant. (2) Both host and parasite were allowed to evolve. (3) Only the parasite's timing was allowed to evolve, while the host was constrained completely. 3. In the first two scenarios, parasite abundances decreased in the course of evolution and reached values well below those found in the field, whereas in the third scenario, parasite abundances were maintained at a level close to that found in the field. In the second scenario (co-evolution), the host seemed to be the leader in the evolutionary race. 4. It is concluded that water mite parasitism is capable of shaping emergence patterns in aquatic insects and, despite the same life-cycle length for host and parasite, the parasite evolves fast enough to shape its hatching pattern to match the emergence pattern of its host. [source]


Darriwilian (Middle Ordovician) graptolite faunas of the Sandia Region, southern Peru

GEOLOGICAL JOURNAL, Issue 4 2010
Jörg Maletz
Abstract Ordovician graptolite faunas of Peru are restricted to a short interval in the Middle to basal Upper Ordovician, found in three regions of the country. All Peruvian graptolite faunas are strongly dominated by shallow water elements of the Atlantic Faunal Realm, represented largely by Didymograptus s. str. and Aulograptus, but a number of faunal elements of the pandemic isograptid biofacies have recently been discovered in the Sandia Region of SE Peru. Peruvian graptolite faunas are reviewed and the new records from the Sandia Region are discussed in detail. The faunas from the Purumpata and Iparo members of the San José Formation range in age approximately from the Undulograptus austrodentatus Biozone to the Holmograptus lentus Biozone (early to middle Darriwilian). The faunas provide a better understanding of faunal composition and diversity in this region and help to correlate shallow water and deeper water graptolite faunas from this time interval. Biserial graptolites are rare in most samples and usually indeterminable, but a single identifiable specimen of Undulograptus austrodentatus was found, indicating a level close to the base of the Darriwilian. A number of specimens of the genera Isograptus and Arienigraptus from the Sandia Region represent pandemic graptolite faunas of the isograptid biofacies, described for the first time from this region. Copyright © 2009 John Wiley & Sons, Ltd. [source]


Adverse trends in male reproductive health: we may have reached a crucial ,tipping point'

INTERNATIONAL JOURNAL OF ANDROLOGY, Issue 2 2008
A.-M. Andersson
Summary Healthy men produce an enormous number of sperms, far more than necessary for conception. However, several studies suggest that semen samples where the concentration of sperms is below 40 mill/mL may be associated with longer time to pregnancy or even subfertility, and specimens where the concentration of sperms is below 15 mill/mL may carry a high risk of infertility. Historic data from the 1940s show that the bulk of young men at that time had sperm counts far above 40 mill/mL with averages higher than 100 mill/mL. However, recent surveillance studies of young men from the general populations of young men in Northern Europe show that semen quality is much poorer. In Denmark approximately 40 percent of the men have now sperm counts below 40 mill/mL. A simulation assuming that average sperm count had declined from 100 mill/mL in ,old times' to a current level close to 40 mill/mL indicated that the first decline in average sperm number of 20,40 mill/mL might not have had much effect on pregnancy rates, as the majority of men would still have had counts far above the threshold value. However, due to the assumed decline in semen quality, the sperm counts of the majority of 20 year old European men are now so low that we may be close to the crucial tipping point of 40 mill/mL spermatozoa. Consequently, we must face the possibility of more infertile couples and lower fertility rates in the future. [source]


Tenascin expression in actinic keratosis

JOURNAL OF CUTANEOUS PATHOLOGY, Issue 11 2006
Maria Lentini
Background:, Tenascin is an extracellular matrix protein frequently expressed around neoplastic and non-neoplastic lesions of the skin. Actinic keratoses (AKs) are intraepidermal neoplastic lesions of the sun-exposed skin. They are classified according to the extension of dysplasia in four stages; they also present different histological varieties. Methods:, We performed an immunohistochemical study using tenascin monoclonal antibody diluted 1 : 50 on 150 cases of AKs classified, respectively, in histotypes (38 hypertrophic, 18 atrophic, 21 bowenoid, 19 acantolytic, and 40 mixed) and in stages (27 stage I, 46 stage II, 42 stage III, and 35 stage IV; 14 in tumoral progression). Results:, Tenascin positivity was observed in all cases at the dermal level close to the epithelial lesion. The intensity of reaction increased from stage I to stage IV and, of course, also in tumoral progression. Its expression was not related to the histotypes. In very few cases, the atypical keratinocytes were positive. Conclusions:, Tenascin expression in AKs is related to the stages of dysplasia. In fact, the immunostaining intensity corresponds to the degree of the dysplasia rather than the thickness of the involved epidermis. Tenascin plays a role in neoplastic progression working as an anti-adhesive factor. [source]


Type 1 von Willebrand disease: application of emerging data to clinical practice

HAEMOPHILIA, Issue 4 2008
P. W. COLLINS
Summary., There has been much recent data published on type 1 von Willebrand disease (VWD) predominantly from three multi-centre cohort studies. These data have influenced a revision of the classification of type 1 VWD and have important implications for the management of this disorder. Patients with low von Willebrand factor (VWF) levels tend to have VWF mutations and VWD is transmitted predictably within families. In patients with VWF levels close to the lower end of the normal range, candidate mutations are found less often, ABO blood group is a more important factor and the disease has variable heritability within families. The importance of bleeding symptoms, in addition to VWF levels, in the diagnosis of type 1 VWD has been highlighted. [source]


Theory of electronic structure of BGaAs and related alloys

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2008
A. Lindsay
Abstract Previous experiments on BxGa1,xAs containing a few percent boron show a dramatic increase in electron effective mass, m*e, similar to that observed in many GaNxAs1,x samples. By contrast, there is a near-linear blue-shift of the energy gap, which can be conventionally described using the virtual crystal approximation. We use a tight-binding model to show that isolated B atoms have little effect either on the band gap or lowest conduction band dispersion in BxGa1,xAs. By contrast, B pairs and clusters introduce defect levels close to the conduction band edge (CBE) which, through a weak band-anticrossing (BAC) interaction, significantly reduce the band dispersion in and around the , -point, thus accounting for the strong increase in m*e and reduction in mobility observed in these alloys. Calculations show that replacing gallium by aluminium shifts the CBE upwards, leading to a large density of B-related states in the energy gap. By contrast, indium shifts the band edge downwards, leading eventually to a band edge m*e close to that predicted by the virtual crystal approximation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]