Cell death in lake phytoplankton communities

1. The fraction of living and dead phytoplankton cells in seven Florida lakes was assessed by using the cell digestion assay, a non‐staining membrane permeability test. The cell digestion assay is an effective method to analyse cell viability in complex natural phytoplankton communities. 2. The lakes examined ranged widely in phytoplankton abundance and community composition. The variability in the percentage of living cells (% LC) was high among the taxonomic groups forming the different phytoplankton communities, ranging from 19.7% to 98% LC. 3. All cells within single cyanobacteria filaments were determined to be either dead or alive, suggesting physiological integration of the cells within colonies. 4. Within each lake, the dominant taxa generally exhibited the highest proportion of living cells. A high proportion of living cells was found to be a characteristic of the different taxa forming the communities of eutrophic lakes. The average value for the % LC for all groups comprising the phytoplankton communities in each of the lakes ranged from 29.9 ± 7.2 to 80.4 ± 4.0 (mean ± SE) and varied strongly and positively with chlorophyll a concentration. 5. These results suggest phytoplankton cell death to be an important process structuring phytoplankton communities in lakes, particularly in oligotrophic ones.     

Characterization of nine microsatellite loci in impala (Aepyceros melampus)

Nine microsatellite loci were isolated from a genomic DNA library created from impala (Aepyceros melampus). Observed and expected levels of heterozygosity were computed utilizing 25 individuals from a population in central Kenya. Tests for Hardy–Weinberg equilibria were conducted and found that three of the nine loci deviated from equilibrium in this population. These markers were developed to analyse the genetic effects of culling and isolation on a game preserve in Kenya.     

THERMODURIC ORGANISMS IN MILK. PART V. A SIMPLIFIED TESTING TECHNIQUE

SUMMARY: Thermoduric colony counts at 30° of laboratory pasteurized milk determined by the roll tube or agar strip methods were lower than those obtained by the standard Petri plate method. The differences in colony count were not of such magnitude, however, as to be likely to result in many errors in grading if a thermoduric bacterial content of greater than 10⁴/ml is accepted as an index of unsatisfactory cleansing of dairy equipment.
The three methods examined were simpler and more economical than the Petri plate technique, but the agar strip method, as described, using the standard loop, was the simplest and gave a sufficiently reliable estimate of the thermoduric colony count for advisory purposes.     

Genetic Control of Chromosome Pairing in Hexaploid Oats

THE common oat, Arena sativa, is a hexaploid (2n=6x=42) whose chromosomes form exclusively bivalents during meiosis. The bivalents are formed by the pairing of exact homologues resulting in disomic inheritance. Gene duplications and triplications were revealed by early inheritance studies¹ and homoeologous relationships of the three genomes were later supported by the good tolerance of deficiency for single and for pairs of chromosomes².     

New Carboniferous fossils of Spilapteridae enlighten postembryonic wing development in Palaeodictyoptera

A new palaeodictyopterid nymph Bizarrea obscura gen.n. et sp.n. (Spilapteridae) and a new adult specimen of Homaloneura cf. dabasinskasi Carpenter are described from the Pennsylvanian (Moscovian) ironstone nodules of Mazon Creek (IL, U.S.A.). Both taxa share enlarged prothoracic lobes (interpreted by some as winglets), heteronomous meso‐ and metathoracic wing pads or wings, a slender abdomen with pointed laterotergites, and a unique division of the abdominal segments by two transverse sulci. An alternative hypothesis for the placement of Bizarrea within Homoiopteridae is considered on the basis of its large body size and relatively short wing pads. Based on the morphology of the new material, postembryonic development of wing pads in Palaeodictyoptera (Palaeodictyopterida) is reconsidered. Detailed investigation of the abdominal segments, including examination by scanning electron microscopy, reveals the presence of subcircular, sclerotized structures partially covered at the bases of the nymphal laterotergites I–VII, ?VIII. Based on their position and shape, these structures are interpreted as abdominal spiracles, and thus a terrestrial or semiaquatic habitat for these immatures is hypothesized. Moreover, our discovery of the same, supposedly homologous structures in the enigmatic Vogesonymphidae (Permoplectoptera), from the Middle Triassic of Grès à Voltzia in France, is evidence for the parallel coexistence of ancestrally terrestrial and derived aquatic lineages of Ephemerida (Ephemeropterida) in early Mesozoic ecosystems. This published work has been registered in ZooBank, http://zoobank.org/urn:lsid:zoobank.org:pub:A7270D99‐5B48‐4EAC‐AEB8‐EFB8A9F55FBD .     

Cat Interferon inhibits Feline Leukaemia Virus Infection in Cell Culture

TRANSMISSION of feline leukaemia can be accomplished with tissue extracts from cases which occur naturally¹. Virus particles which are morphologically indistinguishable from the murine and avian C-type viruses are present in cats with the transmitted disease². Feline leukaemia virus (FeLV) replicates in cat cell cultures³ and infected cells are demonstrable by the indirect immunofiuorescent antibody test which detects FeLV group-specific antigen as granular punctate fluorescence in the cytoplasm of acetone fixed cells⁴; this method allows easy quantitation of the antiviral effect of interferon. We report the production and assay of feline interferon using the fluorescent antibody test with FeLV infected cat cell cultures.     

Stable nitrogen isotope ratios of macrophytes and associated periphyton along a nitrate gradient in two subtropical, spring-fed streams

1. An increase in human population and associated changes in land use have caused an increase in groundwater nitrate concentrations throughout central Florida. Within the region, this nitrate‐laden groundwater returns to the surface via numerous large springs that serve as the origin of flow for many coastal streams and rivers. These rivers can exhibit strong nitrate gradients because of the high nutrient uptake potential of the rivers. 2. We hypothesised that downstream declines in nitrate concentrations would be manifested spatially as increases in the δ¹⁵N of the residual pool of nitrate, macrophytes and periphyton as a consequence of isotopic fractionation associated with preferential use of ¹⁴NO₃⁻. This hypothesis was tested in two spring‐fed river systems, the Chassahowitzka and Homosassa rivers, along Florida's central Gulf of Mexico coast. 3. In general, δ¹⁵N values of nitrate, macrophytes and periphyton increased with decreasing fraction of nitrate remaining in each of the two study systems. The fractionation associated with nitrate uptake by macrophytes and associated periphyton was determined from the relationship between δ¹⁵N of both constituents of the macrophyte community and the fraction of nitrate removed from the system. Values for fractionation by macrophytes and periphyton ranged from 1.9‰ to 3.6‰ and from 0.7‰ to 2.5‰, respectively.     

Characterization of microsatellite loci isolated in trumpeter swan (Cygnus buccinator)

Primers for 16 microsatellite loci were developed for the trumpeter swan (Cygnus buccinator), a species recovering from a recent population bottleneck. In a screen of 158 individuals, the 16 loci were found to have levels of variability ranging from two to seven alleles. No loci were found to be linked, although two loci repeatedly revealed significant departures from Hardy–Weinberg equilibrium. Amplification in the closely related tundra swan (Cygnus columbianus) was successful for all except one locus. These microsatellite loci will be applicable for population genetic analyses and ultimately aid in management efforts.