Inhibitor of the DNA-dependent DNA Polymerase of Some RNA Tumour Viruses in Feline Sera

AN inhibitor of the RNA-dependent DNA polymerases^1,2 of mammalian C-type viruses was found in sera from rats bearing transplantable tumours, induced by murine C-type RNA tumour viruses^3,4. Partially purified polymerases of murine leukaemia virus³ and feline leukaemia virus (FeLV)⁴ were shown to be antigenic in rabbits and a rat, respectively. We have detected an inhibitor of the DNA-dependent DNA polymerase^5,6 of feline and murine C-type viruses in the sera of cats inoculated in utero and/or postnatally with the Gardner-Arnstein strain of feline sarcoma virus (FSV)⁷ and in the sera of cats bearing spontaneous sarcomas, lymphomas or carcinomas.     

Polyploidy and Evolution in Wild and CultivatedDahliaSpecies

Observations on the chromosomes of nine species ofDahliaCav.(Asteraceae, Heliantheae—Coreopsidinae) show that somehave 2n=32, others 2n=64, with a third group having both chromosomenumbers in the same taxon. Karyotype investigations showed thatthe chromosomes can be divided into groups of 14 metacentricsplus two submetacentrics per set of 16 chromosomes.In situhybridizationusing an rRNA gene probe indicated that the 2n=32 species haveeight hybridization sites whilst the 2n=64 species have 16 sites.Silver nitrate staining of these regions showed that not allof these nucleolar organizers are active. Meiotic analysis atmetaphase I and pachytene, by synaptonemal complex spreading,shows that the 2n=32 species have exclusive bivalent formationwhereas the 2n=64 species have small numbers of univalents plusquadrivalents in addition to bivalents. This study proposesthatDahliaspecies with 2n=32 are allotetraploids whereas thosespecies and chromosome races with 2n=64 are their autopolyploidderivatives. We suggest that a bivalent-promoting mechanismin the 2n=32 species may account for their meiotic behaviouras their component genomes appear so similar, and that thismechanism is also responsible for the low number of quadrivalentsin the 2n=64 taxa.Copyright 1998 Annals of Botany Comapny Chromosome pairing,Dahlia, in situhybridization, karyotype analysis, polyploidy, synaptonemal complex analysis     

Growth Characteristics of Axenic Strains of Entamoeba histolytica Schaudinn, 1903*

SYNOPSIS. An account of the culture methods for axenic growth of Entamoeba histolytica is given. Three media, including Diamond's medium, have been reliable. At present 6 strains are maintained axenically; details of isolation and axenization are outlined. Growth characteristics and oxygen requirements of 2 strains are examined.     

Relationship of Obligate Grassland Birds to Landscape Structure in Wisconsin

ABSTRACT Conservation plans for grassland birds have included recommendations at the landscape level, but species' responses to landscape structure are variable. We studied the relationships between grassland bird abundances and landscape structure in 800-ha landscapes in Wisconsin, USA, using roadside surveys. Of 9 species considered, abundances of only 4 species differed among landscapes with varying amounts of grassland and forest. Landscape variables explained <20% of variation in abundances for 4 of the 5 rarest species in our study. Our results suggest landscape-based management plans for grassland birds might not benefit the rarest species and, thus, plans should incorporate species-specific habitat preferences for these species.     

Associations of co-mimetic ithomiine butterflies on small spatial and temporal scales in a neotropical rainforest

To test whether ithomiine butterfly species within Miillerian mimetic classes are associated in space and time, we sampled a community of ithomiine butterflies at monthly intervals with traps in the canopy and the understory of four forest habitats: primary, higrade, secondary and edge. A species accumulation curve reached an asymptote at 22 species, suggesting that these species have a greater preference for feeding on fruit juices than other ithomiines known to occur at the study site. Species richness and individual abundance showed marked temporal variation, and there were slight differences in the distribution of species richness and individual abundance among the four habitats. The 22 species sampled in this study were not stratified vertically. The five mimetic colour classes of these butterflies were unequally distributed among the four habitats and over the course of the twelve months. There is suggestive evidence that co-mimic species occurred in the same habitats, and strong evidence that they occurred at the same times. Habitat and temporal effects each contributed approximately 10% to the total mimetic class diversity, with the temporal effect being slightly larger than that of habitat. This study demonstrates that Müllerian co-mimic associations can be measured on a much smaller scale than has been done previously.