Notes on tropical Africa Cyperaceae

New information relating to structure andor wider distributional records are given for four species of Cyperaceae indigenous to Zambia and/or Zimbabwe. Three are members of tribe Cypereae ( Sphaerocyperus erinaceus, Cyperus albopilosus, C. ciltochty-socephalus); one of Ficineae ( Isolepis trollii ). Tribal delimitation follows that of Goetghebeur (1986).     

A Unified Model of Heading and Path Perception in Primate MSTd

Self-motion, steering, and obstacle avoidance during navigation in the real world require humans to travel along curved paths. Many perceptual models have been proposed that focus on heading, which specifies the direction of travel along straight paths, but not on path curvature, which humans accurately perceive and is critical to everyday locomotion. In primates, including humans, dorsal medial superior temporal area (MSTd) has been implicated in heading perception. However, the majority of MSTd neurons respond optimally to spiral patterns, rather than to the radial expansion patterns associated with heading. No existing theory of curved path perception explains the neural mechanisms by which humans accurately assess path and no functional role for spiral-tuned cells has yet been proposed. Here we present a computational model that demonstrates how the continuum of observed cells (radial to circular) in MSTd can simultaneously code curvature and heading across the neural population. Curvature is encoded through the spirality of the most active cell, and heading is encoded through the visuotopic location of the center of the most active cell''s receptive field. Model curvature and heading errors fit those made by humans. Our model challenges the view that the function of MSTd is heading estimation, based on our analysis we claim that it is primarily concerned with trajectory estimation and the simultaneous representation of both curvature and heading. In our model, temporal dynamics afford time-history in the neural representation of optic flow, which may modulate its structure. This has far-reaching implications for the interpretation of studies that assume that optic flow is, and should be, represented as an instantaneous vector field. Our results suggest that spiral motion patterns that emerge in spatio-temporal optic flow are essential for guiding self-motion along complex trajectories, and that cells in MSTd are specifically tuned to extract complex trajectory estimation from flow.     

Seroprevalence of Sheep and Goat Pox,Peste Des Petits Ruminants and Rift Valley Fever in Saudi Arabia

Sheep and goat pox, peste des petits ruminants and Rift Valley fever are important diseases of small ruminant livestock. Sheep and goat pox, along with peste des petits ruminants, are endemic throughout most of Africa, Asia and the Middle East. Whereas Rift Valley fever is endemic in Africa, outbreaks in the Middle East have been reported over the past decade, including the Arabian Peninsula. Saudi Arabia is a major importer of livestock, and understanding the prevalence of these viral infections would be useful for disease control. In this study, sera from sheep and goats were collected from 3 regions in Saudi Arabia. They were evaluated for antibodies specific to sheep and goat pox, peste des petits ruminants and Rift Valley fever by virus neutralization assays. To the best of our knowledge, this is the first study to evaluate the seroprevalence of these viruses in sheep and goats.     

Additive Genetic Variation in Schizophrenia Risk Is Shared by Populations of African and European Descent

To investigate the extent to which the proportion of schizophrenia’s additive genetic variation tagged by SNPs is shared by populations of European and African descent, we analyzed the largest combined African descent (AD [n = 2,142]) and European descent (ED [n = 4,990]) schizophrenia case-control genome-wide association study (GWAS) data set available, the Molecular Genetics of Schizophrenia (MGS) data set. We show how a method that uses genomic similarities at measured SNPs to estimate the additive genetic correlation (SNP correlation [SNP-r_g]) between traits can be extended to estimate SNP-r_g for the same trait between ethnicities. We estimated SNP-r_g for schizophrenia between the MGS ED and MGS AD samples to be 0.66 (SE = 0.23), which is significantly different from 0 (p_{(SNP-rg = 0)} = 0.0003), but not 1 (p_{(SNP-rg = 1)} = 0.26). We re-estimated SNP-r_g between an independent ED data set (n = 6,665) and the MGS AD sample to be 0.61 (SE = 0.21, p_{(SNP-rg = 0)} = 0.0003, p_{(SNP-rg = 1)} = 0.16). These results suggest that many schizophrenia risk alleles are shared across ethnic groups and predate African-European divergence.     

Post-genomic Pseudomonas

A report on the 19th Whitehead Institute Symposium, Cambridge, USA, 14-16 October 2001.