Albumin and Australian frogs: molecular data a challenge to speciation model

Vertebrate speciation in the southwest of Australia has long been viewed as resulting from multiple invasions of eastern source stocks during the Pleistocene. Microcomplement fixation studies of serum albumin evolution in frogs of the genus Heleioporus provide the first hard data on age and phylogenetic relationships among species in this genus and lead to rejection of the multiple invasion model in favor of speciation occurring in Western Australia. The albumin molecular clock was used to estimate that the species divergences in this genus occurred between 4 million to 12 million years ago in the late Tertiary (Pliocene-Miocene), rather than in the Quaternary (the last 2 million years).     

Gibbon fibrinopeptides: identification of a glycine-serine allelism at position B-3

The fibrinopeptides A and B of the gibbon (an Asian ape) have been characterized and their relation to other primate types examined. An allelic situation was discovered at location B-3; two of the gibbons studied had both glycine and serine at that position, whereas four others were homozygous for glycine.     

Cognitive inflexibility after prefrontal serotonin depletion

Serotonergic dysregulation within the prefrontal cortex (PFC) is implicated in many neuropsychiatric disorders, but the precise role of serotonin within the PFC is poorly understood. Using a serial discrimination reversal paradigm, we showed that upon reversal, selective serotonin depletion of the marmoset PFC produced perseverative responding to the previously rewarded stimulus without any significant effects on either retention of a discrimination learned preoperatively or acquisition of a novel discrimination postoperatively. These results highlight the importance of prefrontal serotonin in behavioral flexibility and are highly relevant to obsessive-compulsive disorder, schizophrenia, and the cognitive sequelae of drug abuse in which perseveration is prominent.     

The potential for systems and modelling research in pasture science in South Africa

The availability of computers has made it possible to process large volumes of complex data. This development has enabled scientists to enter the field of systems research which both analyses and synthesises complex multivariate agricultural production systems. By building models which represent real systems and by simulating the internal processes of each component of the system, systems research can be used in prediction, decision-making, developing new production methods and teaching. The potential use of modelling in the field of pasture science in South Africa deserves careful evaluation, in view of the complexity, expense and long-term nature of traditional grazing experiments. There is a place for modelling by inter-disciplinary teams in local research, in spite of the present shortcomings of this recently-developed approach.     

Terrestrial field dissipation of diclosulam at four sites in the United States.

The soil dissipation of diclosulam was studied using 14C-labeled and nonradiolabeled material in Mississippi, North Carolina, Georgia, and Illinois between 1994 and 1997. The test substance was preemergence broadcast applied at target rates of 35 and 37 g ai x ha(-1) for the 14C-labeled and the nonradiolabeled studies, respectively. The degradation of diclosulam was rapid with half-lives ranging from 13 to 43 days at the four sites. Rapid degradation rates and the increasing sorption to soil over time resulted in low persistence and mobility of this compound. Metabolite formation and dissipation in the field reflected observations of photolysis, hydrolysis, and aerobic soil metabolism studies in the laboratory. The rapid field dissipation rates, metabolite formation patterns, and sorption characteristics obtained in these field studies were consistent with the laboratory data generated for diclosulam, and reflect the multiple concurrent degradation mechanisms occurring in the field.     

Genetic diversity of cowpea [<Emphasis Type="Italic">Vigna unguiculata</Emphasis> (L.) Walp.] in four West African and USA breeding programs as determined by AFLP analysis

Cowpea is an important grain legume and hay crop of many tropical and subtropical regions, especially in the dry savanna region of West Africa. The cowpea gene pool may be narrow because of a genetic bottleneck during domestication. Genetic variation within specific breeding programs may be further restricted due to breeding methods, ‘founder effects’ and limited exchange of germplasm between breeding programs. Genetic relationships among 60 advanced breeding lines from six breeding programs in West Africa and USA, and 27 landrace accessions from Africa, Asia, and South America were examined using amplified fragment length polymorphism (AFLP) markers with six near infrared fluorescence labeled EcoRI + 3/1bases/MseI + 3/1bases primer sets. A total of 382 bands were scored among the accessions with 207 polymorphic bands (54.2%). Despite a diverse origin, the 87 cowpea accessions shared a minimum 86% genetic similarity. Principal coordinates analysis showed clustering of breeding lines by program origin, indicating lack of genetic diversity compared to potential diversity. Accessions from Asia and the Americas overlapped and were distinct from West African breeding lines, indicating that germplasm from Asia and the Americas have common origins outside West Africa. US and Asian breeding programs could increase genetic variability in their programs substantially by incorporating germplasm from West Africa, while national programs in West Africa should consider introgression of Asian germplasm and germplasm from other parts of Africa into their programs to ensure long-term gains from selection.     

Soils and plant nutrition on a serpentinized ridge in South Germany. I. Soils

The soil association is described for a serpentinized ridge and its adjacent upper slopes in Northeastern Bavaria (Germany). On gentle and moderately inclined parts of the relief medium to deeply weathered Eutric Cambisols dominate. Specific properties are the unusually high Mg saturation values (35 – 85 %) and Mg/Ca (exchangeable) ratios (1.6 – 10.8) in the mineral soil horizons. Steeper parts of the slopes are characterized by Rego-Eutric Cambisols and Eutric Regosols. Eutric Leptosols dominate the footslope of a quarry.