Cell adhesion molecule in the hexactinellid Aphrocallistes vastus

Abstract. The Hexactinellida sponge Aphrocallistes vastus contains a soluble aggregation factor (AF) whose purification has been described in this communication. It is characterized by a S°_20.w value of 37 and a buoyant density of 1.45 g/cm³. The AF is a glycoporteinaceous particle composed of three major protein species; no core structure could be visualized. In the presence of Ca²⁺, the AF causes secondary aggregation of single cells. The aggregation process is temperature, pH, and ionic strength independent within a broad range. Evidence is presented indicating that two (or more) AF molecules are required for the establishment of a stable cell: cell interaction. In contrast to the AFs from demosponges, the hexactinellid AF functions species-unspecifically.     

New species of Passiflora subg. Plectostemma and subg. Tacsonia (Passifloraceae)

Five new species of Passiflora subgenera Plectostemma and Tacsonia from Ecuador are described, viz. P. discophora, P. monadelpha, P. subpurpurea, P. hirtiflora and P. sanctaebarbarae . Section Discophora of subg. Plectostemma is proposed.     

Population structure,dispersal and colonization history of the garden bumblebee <Emphasis Type="Italic">Bombus hortorum</Emphasis> in the Western Isles of Scotland

New methods of analysing genetic data provide powerful tools for quantifying dispersal patterns and reconstructing population histories. Here we examine the population structure of the bumblebee Bombus hortorum in a model island system, the Western Isles of Scotland, using microsatellite markers. Following declines in other species, B. hortorum is the only remaining long-tongued bumblebee species found in much of Europe, and thus it is of particular ecological importance. Our data suggest that populations of B. hortorum in western Scotland exist as distinct genetic clusters occupying groups of nearby islands. Population structuring was higher than for other bumblebee species which have previously been studied in this same island group (F_st = 0.16). Populations showed significant isolation by distance. This relationship was greatly improved by using circuit theory to allow dispersal rates to differ over different landscape features; as we would predict, sea appears to provide far higher resistance to dispersal than land. Incorporating bathymetry data improved the fit of the model further; populations separated by shallow seas are more genetically similar than those separated by deeper seas. We argue that this probably reflects events following the last ice age when the islands were first colonized by this bee species (8,500–5,000 ybp), when the sea levels were lower and islands separated by shallow channels would have been joined. In the absence of significant gene flow these genetic clusters appear to have since diverged over the following 5,000 years and arguably may now represent locally adapted races, some occurring on single islands.     

The organization and structure of nerve and muscle in the jellyfish Cyanea capillata (coelenterata; scyphozoa)

The perirhopalial tissue and swimming muscle of Cyanea were examined with light microscopical and electron microscopical techniques. The perirhopalial tissue is a thin, triangular septum found on the subumbrellar surface of the animal. It separates part of the gastric canal system from the surrounding seawater, and is bound on two sides by radial muscle bands and on the third, the shorter side, by a rhopalium and the margin of the bell. The ectoderm of the perirhopalial tissue is composed of large, somewhat cuboidal, vacuolated, myoepithelial cells. The muscle tails of these cells form a single layer of radial, smooth muscle. Neurons of the “giant fiber nerve net” (GFNN), which form an extensive net over the perirhopalial tissue, lie at the base of the vacuolated portion of the myoepithelial cells. These neurons are visible in living tissue. The morphology of individual GFNN neurons was examined following intracellular injection of the fluorescent dye Lucifer Yellow. The neurons are usually bipolar and free of branches. At the electron microscope level, one usually finds that the GFNN neurons contain large vacuoles. The other characteristic feature of these cells is that they form symmetrical, or nonpolarized, synapses; that is, synaptic vesicles are found on both sides of the synapse. The swimming muscle is striated and composed of myoepithelial cells. Each myoepithelial cell has several muscle tails, and those of adjacent cells are linked to gether by desmosomes. The endoderm of the perirhopalial tissue also was examined. This investigation of the organization and ultrastructure of the perirhopalial tissue and surrounding muscle was undertaken to provide essential background information for an ongoing physiological study of the GFNN neurons and their synapses.     

Mechanisms of madness: evolutionary psychiatry without evolutionary psychology

Delusions are currently characterised as false beliefs produced by incorrect inference about external reality (DSM IV). This inferential conception has proved hard to link to explanations pitched at the level of neurobiology and neuroanatomy. This paper provides that link via a neurocomputational theory, based on evolutionary considerations, of the role of the prefrontal cortex in regulating offline cognition. When pathologically neuromodulated the prefrontal cortex produces hypersalient experiences which monopolise offline cognition. The result is characteristic psychotic experiences and patterns of thought. This bottom-up account uses neural network theory to integrate recent theories of the role of dopamine in delusion with the insights of inferential accounts. It also provides a general model for evolutionary psychiatry which avoids theoretical problems imported from evolutionary psychology.