Potential Divergence (potential + divergence)

Distribution by Scientific Domains

Selected Abstracts


EVOLUTION, Issue 8 2007
S. Bergek
Gene flow between coexisting or nearby populations normally prevents genetic divergence and local adaptation. Despite this, there are an increasing number of reports of sympatric sister taxa, indicating potential divergence and speciation in the face of gene flow. A large number of such reported cases involve lake-dwelling fish, which are expected to run into few physical barriers to dispersal within their aquatic habitat. However, such cases may not necessarily reflect sympatric speciation if cryptic dispersal barriers are common in lakes and other aquatic systems. In this study, we examined genetic differentiation in perch (Perca fluviatilis L.) from nine locations in a single, small lake (24 km2), using microsatellites. We detected significant genetic differentiation in all but two pairwise comparisons. These patterns were not consistent with divergence by distance or the existence of kin groups. Instead, they suggest that cryptic barriers to dispersal exist within the lake, allowing small-scale genetic divergence. Such an observation suggests that allopatric (or parapatric) divergence may be possible, even in small, apparently homogenous environments such as lakes. This has important consequences for how we currently view evidence from nature for sympatric speciation. [source]

Selectivity and competitive interactions between two benthic invertebrate grazers (Asellus aquaticus and Potamopyrgus antipodarum): an experimental study using 13C- and 15N-labelled diatoms

Summary 1. Tracer experiments with two diatoms labelled with 13C (Nitzschia palea) and 15N (Fragilaria crotonensis), were conducted to investigate feeding selectivity and interspecific competition between the grazers Asellus aquaticus (Isopoda, Crustacea) and Potamopyrgus antipodarum (Hydrobiidae, Gastropoda). Conventional methods, such as cell counts and estimated biovolume, were used first to detect feeding preferences within the different grazer treatments. 2. The results revealed a significant decline in algal biovolume in all grazer treatments and no indications of active selectivity were observed. In contrast to conventional methods, measurements based on isotope signatures showed strong differences in tracer uptake, thus indicating different degrees of assimilation and digestion by the two grazers. 3. The selectivity index Q, which provides information on the uptake ratio of 13C to 15N, showed a significant time effect for both grazer species and a significant difference between single- and mixed-grazer treatments for P. antipodarum. Thus, this technique enabled the direct quantification of the uptake by grazers and, therefore, served as an ideal tool for the detection of passive selectivity. 4. Our results indicate a shift in feeding preferences related to between-species competition and a potential divergence of trophic niches when species coexist. [source]

What are teenagers reading?

LITERACY, Issue 3 2005
Adolescent fiction reading habits, reading choices
Abstract What are adolescents choosing to read? This is an important question because of potential divergence between school students' reading interests and reading expectations in school. This article considers the findings from a study of the reading over one week in May 2002 of 707 school students aged between 11 and 15, undertaken in 30 schools in the south-west of England. The findings are related to earlier research by, amongst others, Whitehead, Benton, and Hall and Coles. The article reflects on adolescent reading choices, influences on those choices and the importance of validating all reading experience, including the new literacies. [source]

Identification and Characterization of Kava-derived Compounds Mediating TNF- , Suppression

Michael P. Pollastri
There is a substantial unmet need for new classes of drugs that block TNF- , -mediated inflammation, and particularly for small molecule agents that can be taken orally. We have screened a library of natural products against an assay measuring TNF- , secretion in lipopolysaccharide-stimulated THP-1 cells, seeking compounds capable of interfering with the TNF- , -inducing transcription factor lipopolysaccharide-induced TNF- , factor. Among the active compounds were several produced by the kava plant (Piper mysticum), extracts of which have previously been linked to a range of therapeutic effects. When tested in vivo, a representative of these compounds, kavain, was found to render mice immune to lethal doses of lipopolysaccharide. Kavain displays promising pharmaceutical properties, including good solubility and high cell permeability, but pharmacokinetic experiments in mice showed relatively rapid clearance. A small set of kavain analogs was synthesized, resulting in compounds of similar or greater potency in vitro compared with kavain. Interestingly, a ring-opened analog of kavain inhibited TNF- , secretion in the cell-based assay and suppressed lipopolysaccharide-induced TNF- , factor expression in the same cells, whereas the other compounds inhibited TNF- , secretion without affecting lipopolysaccharide-induced TNF- , factor levels, indicating a potential divergence in mechanism of action. [source]