Testing the accuracy of methods for reconstructing ancestral states of continuous characters.

Many methods are available for estimating ancestral values of continuous characteristics, but little is known about how well these methods perform. Here we compare six methods: linear parsimony, squared-change parsimony, one-parameter maximum likelihood (Brownian motion), two-parameter maximum likelihood (Ornstein-Uhlenbeck process), and independent comparisons with and without branch-length information. We apply these methods to data from 20 morphospecies of Pleistocene planktic Foraminifera in order to estimate ancestral size and shape variables, and compare these estimates with measurements on fossils close to the phylogenetic position of 13 ancestors. No method produced accurate estimates for any variable: estimates were consistently less good as predictors of the observed values than were the averages of the observed values. The two-parameter maximum-likelihood model consistently produces the most accurate size estimates overall. Estimation of ancestral sizes is confounded by an evolutionary trend towards increasing size. Shape showed no trend but was still estimated very poorly: we consider possible reasons. We discuss the implications of our results for the use of estimates of ancestral characteristics.     

Microdissection and microcloning from the proximal region of mouse chromosome 7: isolation of clones genetically linked to the pudgy locus

Microdissection and microcloning have been utilized in order to create a bank of clones from the proximal region of mouse chromosome 7. Several important loci map to this area, including the albino locus (c), pink-eye dilution (p), and the developmental mutant, pudgy (pu). By use of interspecific crosses between Mus musculus domesticus and Mus spretus, we have generated backcross progeny segregating for the mutations chinchilla (cch) and pink-eye dilution (p). Exploiting the evolutionary divergence between the two species, we have analyzed the inheritance of restriction fragment length variants of three microclones and their linkage to the two markers cch and p, respectively. All three clones studied map to the dissected region, and as such also show genetic linkage to the pudgy locus. This bank of chromosome 7-derived microclones should provide molecular start points for the isolation of a variety of developmental loci of unknown gene product, including the pudgy locus.     

Effects of growth state and amines on cytoplasmic and vocuolar pH, phosphate and polyphosphate levels in Saccharomyces cerevisiae: a P-nuclear magnetic resonance study

The vacuoles of logarithmic and stationary stage cells were compared by ³¹P-NMR with regard to pH, orthophosphate (P_i) content and average size of polyphosphate. The vacuoles of stationary cells had lower pH higher P_i content, and polyphosphates of longer average chain lenght, although total polyphosphate content was about the same as in logarithmic cells. The lower vacuolar pH in stationary cells was the major cause of a larger cytoplasmic-vacuolar pH gradient. Addition of NH₄Cl, (NH₄)₂SO₄, methylamine or amantadine at pH 8 to cells in either stage caused an icnrease in both cytoplasmic and vacuolar pH, with little or no change in the cytoplasmic-vacuolar pH gradient. However, the administration of ammonium salts to the cells at pH 8.0 resulted in rapid hydrolysis of the intravacuolar polyphosphate to tripolyphosphate and P_i, with attendant redistribution of P_i between the vacuolar and cytoplasmic compartments.     

Persistence of infection in mice inoculated intranasally with Cryptococcus neoformans

Cryptococcus neoformans was instilled intranasally into mice which were periodically sacrificed to determine the course of infection. Cryptococci persisted within the nasal passages throughout the 90 day study. Extranasal dissemination began 14–28 days after instillation and was still demonstrable 90 days post-exposure. Ten percent mortality was observed in mice receiving 10⁶ cryptococci, while no mortality was observed in mice exposed to 10³ or 10⁴ cryptococci. Our research suggests that nasal colonization with C. neoformans can precede pulmonary and systemic cryptococcosis by weeks or months.     

Determination of effective diffusivity of substrate in biological films and particles

Summary Particle supported biofilms of uniform thickness were generated in an aerobic fluidized-bed reactor with phenol as the carbon source. A method was developed for determining the effective diffusivities of oxygen and phenol using trypan blue, a vital stain as the tracer. The effective diffusivities of oxygen and phenol were found to be 2.72×10^–6 cm²/s and 1.12×10^–6 cm²/s respectively.Nomenclature C_i initial solute concentration in bulk, g/cm³ - C_t solute concentration in bulk at time t, g/cm³ - C bulk solute concentration at equilibrium, g/cm³ - D molecular diffusivity, cm²/s - D effective diffusivity, cm²/s - D_o D_p D_tb molecular diffusivity of oxygen, phenol and trypan blue, cm²/s - D_o, D_p, D_tb effective diffusivity of oxygen, phenol and trypan blue, cm²/s - D_s molecular diffusivity of substrate, cm²/s - D_s effective diffusivity of substrate, cm²/s - K partition coefficient - M_t amount of solute in the particle at time t, g - M amount of solute in the particle at equilibrium, g - r particle radius, cm - r _bp radius of the particle with biofilm, cm - S substrate concentration, g/cm³ - S_b substrate concentration in bulk, g/cm³ - S_i initial substrate concentration, g/cm³ - V₁ solute molar volume, cm³/g mol Greek Symbols bf porosity of the biofilm - tortuosity factor